Trade-off between local persistence and rapid expansion: a case study of a parthenogenetic lizard species and its sexually reproducing ancestor

Trade-off between local persistence and rapid expansion: a case study of a parthenogenetic lizard species and its sexually reproducing ancestor | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Trade-off between local persistence and rapid expansion: a case study of a parthenogenetic lizard species and its sexually reproducing ancestor Natia Barateli, David Tarkhnishvili, Giorgi Iankoshvili This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9127021/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 9 You are reading this latest preprint version Abstract Parthenogenetic lineages are often portrayed as rapid colonizers with short lifespans, but how reproductive mode shapes life-history trajectories in close relatives remains unclear. Using Caucasian rock lizards ( Darevskia ) as a model, we compared age structure, growth dynamics, and reproductive traits in the hybrid parthenogenetic lizard ( D. armeniaca ) and its sexually breeding progenitors ( D. valentini , D. mixta ). Age was inferred by skeletochronology of phalangeal cross-sections; growth was estimated from distances between successive lines of arrested growth (LAGs). Reproductive traits were integrated from published datasets and re-analyzed. Parthenogenetic lineages tended to show age distributions consistent with earlier maturation, higher reproductive allocation, and shorter lifespan than their sexual relatives. D. armeniaca showed higher reproductive effort relative to body mass, earlier age of maturation, and lower proportion of individuals with long lifespan than its patrilineal progenitor, D. valentini from the same location. Population modeling suggests that the parthenogens would expand faster throughout neighboring habitats than the sexual breeders, which is in line with the observation that they occupy a greater fraction of suitable habitat within their ranges. These differences suggest a demographic mechanism by which unisexual lineages may expand faster, whereas sexual lineages may persist longer under variable conditions, potentially contributing to their long-term coexistence. life-history trade-offs demographic strategy age structure parthenogenesis Darevskia Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Parthenogenetic lineages often differ in key life-history traits from closely related sexual breeders. Usually, they have shorter generations, start reproducing at a younger age, and have higher intrinsic rates of population increase (r) (Maynard Smith, 1978 ). Such patterns have been reported for many short-lived, asexual or facultative parthenogenetic invertebrates, including aphids and some rotifers (Hughes, 1963 ; Williams, 1975 ; Bell, 1982 ). Rather than increasing lifespan or the total number of reproductive seasons, both obligate and cyclical parthenogens invest proportionally more in early and rapid reproduction, a strategy that may enhance short-term population growth and facilitate rapid spatial expansion (Cuellar, 1977 ; Vrijenhoek, 1998 ; Doroszuk et al., 2006 ; Stelzer, 2011 ; Roark & Bjorndal, 2014 ). These observations are consistent with theoretical expectations that asexual reproduction may be associated with rapid demographic responses under stable, optimal conditions, whereas sexual reproduction is more often associated with slower population growth but greater long-term evolutionary adaptability in changing environments (Williams, 1975 ; Maynard Smith, 1978 ; Cuellar, 1977 ; Bell, 1982 ; Otto, 2009 ). In vertebrates, and particularly in parthenogenetic lizards, the relationship between reproductive mode and life-history traits appears to be more complex. Vertebrates are characterized by longer lifespans, delayed maturation, and repeated reproductive seasons, which may decouple short-term reproductive output from lifetime fitness. Consequently, the demographic effects of parthenogenesis in vertebrates are expected to depend on complex trade-offs among age at maturity, fecundity, survival, and reproductive longevity. Empirical studies of parthenogenetic lizards illustrate this complexity. Wright and Lowe ( 1968 ) showed that parthenogenetic Aspidoscelis tesselata start reproducing earlier in life than the related bisexual species A. sexlineata under similar environmental conditions. However, A. tesselata reaches maturity at a smaller body size (and presumably earlier age) and produces smaller clutches. This example illustrates that differences in reproductive mode may involve compensating changes among life-history components (e.g., earlier maturation versus clutch size), and the resulting lifetime reproductive output may depend on additional factors such as clutch frequency and longevity. A triploid parthenogen, A. neotesselata , exhibits clutch sizes comparable to its sexual ancestor, A. patrilineata , differing from its diploid parthenogenetic predecessor A. tesselata (Taylor et al., 2006 ). Kearney and Shine ( 2005 ) demonstrated that parthenogenetic geckos of the Heteronotia binoei complex have smaller clutch sizes than their sexually reproducing relatives, suggesting that earlier reproduction does not necessarily translate into greater reproductive output, because different components of life history may change in compensatory ways. Taken together, these findings indicate that lizard parthenogens and their sexual relatives cannot be simply placed at opposite ends of a simple r–K continuum (sensu Pianka, 1970 ; Roff, 1992 ). Instead, differences between reproductive modes may be better described with a multidimensional life-history framework involving trade-offs among traits such as age at maturity, generation time, survival dynamics, reproductive lifespan or senescence, egg size, clutch size, and clutch frequency. Caucasian rock lizards of the genus Darevskia represent one of the best-studied vertebrate systems comprising multiple sexually reproducing species and several parthenogenetic lineages of hybrid origin (Darevsky, 1967 ; Murphy, 2000; Tarkhnishvili et al., 2020 ; Freitas et al., 2022 ; Yanchukov et al., 2022 ). Parthenogenetic species of this genus commonly coexist with their patrilineal ancestors, i.e., the paternal sexual species involved in their hybrid origin (Darevsky, 1967 ; Danielyan et al., 2008 ; Tarkhnishvili et al., 2010 ; Barateli et al., 2021 , 2024 ; Arakelyan et al., 2023 ; Galoyan et al., 2025 ). In southern Georgia, two parthenogenetic species ( Darevskia armeniaca and D. dahli ) share habitats with their paternal sexual ancestors ( D. valentini and D. portschinskii , respectively). This system therefore provides an opportunity to compare life-history traits between parthenogenetic lineages and their sexual progenitors under broadly comparable environmental conditions. Both parthenogenetic species share the same matrilineal ancestor, D. mixta . Although geographically close to the ranges of the studied species, D. mixta does not overlap spatially with either the parthenogenetic lineages or their paternal ancestors. A previous study (Barateli et al., 2022 ) revealed different patterns of divergence in reproductive traits between the parthenogen and its patrilineal ancestor. D. armeniaca exhibited significantly higher reproductive effort (clutch mass relative to female body mass) than D. valentini , while egg size did not differ between the species. This finding led to the hypothesis that increased reproductive effort may reduce adult female survival to subsequent breeding seasons, whereas larger egg size may enhance juvenile survival; however, these hypotheses remain largely untested. Such trade-offs between current reproductive investment, growth, and survival is central to life-history theory (Stearns, 1992 ; Roff, 1992 ) and may shape differences in demographic strategy between parthenogenetic and sexual lineages. In this study, we focus primarily on the sympatric species pair consisting of the parthenogenetic Darevskia armeniaca and its bisexual paternal ancestor D. valentini , co-occurring at the same site in southern Georgia (Fig. 1 ). All main statistical analyses are centered on this sympatric system. Other taxa, including the matrilineal ancestor of the parthenogen, D. mixta , and another pair of parthenogenetic species and its patrilineal ancestor, namely D. dahli and D. portschinskii , are used only for contextual comparison. We restricted most analyses to adult females from populations occupying the same habitat. With this approach, we aimed to minimize environmental confounding and isolate species-level differences in life-history traits. Using skeletochronological data, we compared age structure and growth patterns of these species to test whether parthenogenetic D. armeniaca exhibits demographic traits consistent with a faster life-history pace relative to its bisexual ancestor. Specifically, we hypothesize that, in sympatry, D. armeniaca will show (1) earlier age at maturity, (2) shorter generation time and shorter lifespan, and (3) initially rapid but more strongly decelerating growth compared to females of the patrilineal species D. valentini . By analyzing the relative distribution patterns of the two species, we assess whether these differences in life history may influence the spatial distribution of the parthenogen and its paternal ancestor. We also use simple demographic simulations to illustrate how observed life-history differences may translate into contrasting short-term population trajectories. Materials and Methods Study system and sampling design This study focuses on a location from the surroundings of Saghamo Lake (from here onwards “Saghamo”, ~ 2000 m a.s.l. Figure 1 c, Table 1 ) where D. armeniaca and D. valentini occur sympatrically and syntopically. The two species were observed at broadly similar frequencies during field observations in 2025: from 154 individuals observed and photographed, D. armeniaca was 49.3%, females of D. valentini 31.2%, and males of D. valentini − 19.5%. Table 1 Sample locations and sample sizes (see also Fig. 1 ). TC- Total Count of Samples; SCY - Sample Count by Years. Only reproductive females were sampled. Species Location Lat °N) Long (°E) m a.s.l. TC SCY 2023 2024 2025 D. armeniaca Saghamo Lake 41.29° 43.73° 2015 31 16 15 - D. armeniaca Kirkhbulakhi 41.23° 43.28° 1715 7 - 7 - D. dahli Kojori 41.64° 44.68° 1120 18 8 10 - D. mixta Bakuriani 41.79° 43.47° 1281 13 1 - 12 D. portschinskii Kojori 41.64° 44.68° 1120 5 2 - 3 D. portschinskii Tana 41.84° 43.85° 1358 14 - 14 - D. valentini Saghamo Lake 41.29° 43.73° 2015 32 10 22 - Field sampling was conducted during the reproductive season (May-June) in 2023–2025. Adult females were captured by hand. Sample sizes are shown in Table 1 . We concentrated on adult gravid females, identified by manual palpation of the abdomen; individuals were confirmed as gravid by the presence of detectable eggs. Observations from another species pair, parthenogenetic D. dahli and its paternal ancestor D. portschinskii that also coexist in Georgia, were not included in statistical analyses because the sample size of the sexual species ( D. portschinskii ) was too small for reliable comparison. These data are therefore presented only descriptively in the supplementary material, and used for illustrating the differences in body size and geographic distribution. Notably, field observations suggest that D. dahli may locally reach higher densities than its sexual ancestor D. portschinskii in areas where the two species coexist (Tarkhnishvili et al., 2010 ), although the limited sample size in the present dataset does not allow us to evaluate this pattern quantitatively. Morphological measurements and tissue sampling For each individual, snout–vent length (SVL) was measured to the nearest 0.1 mm using digital calipers. Sex was determined based on secondary sexual characteristics (presence of hemipenes and enlarged femoral pores). The fourth phalanx of the right lower toe was clipped from each live individual, as recommended by Castanet & Smirina ( 1990 ); Beaupre et al. ( 2004 ). The diameter of the 4th phalanx in these lizards varies between 0.3–0.8 mm and clipping never causes bleeding. Most of the animals were released at the capture site immediately after sampling. Five females of each species were transported to the lab and kept captive before being released. None of them showed any sign of inflammation. Each individual was sampled only once; individuals were not marked or recaptured. Skeletochronology and age estimation Skeletochronology is widely regarded as the most reliable method for age determination in reptiles (Guarino & Mezzasalma, 2025 ). Age was estimated using skeletochronology following standard protocols used for inferring age in reptiles (Castanet and Smirina, 1990 ; Arakelyan & Danielyan, 2000 l et al., 2014 ). Phalanges were decalcified in 5% nitric acid (40 min for small-bodied species and up to 1 h for larger-bodied species), rinsed in tap water for more than 12 h, and sectioned at 18–20 µm thickness using a freezing microtome. Sections were stained with Ehrlich’s hematoxylin (20 min), mounted in glycerin, and sealed with a coverslip. Digital images were obtained under a light microscope equipped with a digital camera. Lines of arrested growth (LAGs; concentric rings formed in bone tissue during seasonal pauses in growth during hibernation) were counted on transverse sections of the diaphysis. Because one LAG is generally formed per year, the number of LAGs provides an estimate of individual age. Only clearly visible, continuous lines were considered annual growth marks. Faded or discontinuous rings were excluded, and double lines were interpreted as a single annual growth cycle following established criteria (Castanet and Smirina, 1990 ). Representative cross-sections are shown in Fig. 2 . Growth dynamics were inferred from inter-annuli distances (DIVs), defined as the distances between successive LAGs. DIVs represent annual growth increments and therefore provide an estimate of somatic growth achieved during each year of life, and serve for analyses of growth rates and growth deceleration across age classes and species. All individual-level morphometric and skeletochronological data for D. armeniaca, D. valentini, D. mixta, D. dahli , and D. portschinskii are provided in Supplementary Data (Table S1 ). To assess age structure, we compared the relative frequencies of individuals with different numbers of LAGs across species. Reproduction Reproductive traits analyzed in this study were based on the dataset published in Barateli et al. ( 2022 ), collected from the same populations as the present skeletochronological samples, although from different individuals. In that study, gravid females were temporarily maintained in small tanks until oviposition, freshly deposited eggs were measured and weighed, and females and hatchlings were subsequently released at their site of capture. The variables used here were egg size, clutch size, clutch mass, and reproductive effort (RE), defined as clutch mass divided by female body mass prior to oviposition. No new reproductive data were collected for the present study. Instead, we used the original dataset of Barateli et al. ( 2022 ) and, where relevant, reanalyzed it to compare distributions of reproductive effort between species from Saghamo. No additional published reproductive datasets were used. Mapping the ranges To evaluate whether differences in life-history traits between parthenogenetic species and their sexual ancestors are associated with differences in spatial distribution, we compared the proportion of occupied grid cells within each species' extent of occurrence (EOO). Occurrence records compiled from previous publications (Darevsky, 1967 ; Tarkhnishvili et al., 2010 , 2013 ; Tarkhnishvili & Iankoshvili, 2023 ) were plotted on a 5 × 5 km grid. We separated the squares where both species of the pair, only the parthenogen or the paternal ancestor, were found. For mapping, we used QGIS software (QGIS Development Team, version 3.34, 2024). For contextual comparison, analogous occupancy map is also shown for D. dahli and D. portschinskii . Statistical analysis (1) We compared age distributions between species and years using cumulative link models, treating the number of LAGs as an ordered response variable. Species, year, and interaction between species*year were used as predictors. The frequencies of each age class were used as weights in the model. This approach allowed all age classes to be analyzed simultaneously. Because some age classes were rare, contingency-table tests based on Fisher’s exact test with Monte-Carlo simulation (10,000 replicates) were additionally used to compare species-specific age distributions within each year and to test year-to-year changes within each species. As a secondary descriptive comparison, we also summarized the proportion of the youngest adult females (≤ 3 LAGs), corresponding to the earliest reproductive age, in D. armeniaca , D. valentini , and D. mixta . These comparisons were used only to illustrate broad differences in age structure and were evaluated with directional z-tests and Fisher’s exact tests. All analyses were performed in R 4.5.2 (packages ordinal, dplyr, tidyr, ggplot2 ). (2) We compared adult female body length (SVL) among the species (five species included – D. armeniaca with its parental species, D. dahli , and D. portschinskii ) and age classes ( D. armeniaca and D. valentini ) using General Linear Model (species and age/ LAGs number used as predictors) and, where appropriate, the Welch two-sample t-test. Because adult SVL is the cumulative outcome of growth over multiple years, these analyses were used to assess whether age structure and growth patterns were reflected in final adult size. (3) We analyzed annual growth increments (DIV1–DIV6) using linear mixed-effects models in R 4.5.2. Each individual contributed several measurements corresponding to successive inter-LAG distances recorded from the same phalanx section; because these increments originate from the same individual and are therefore not statistically independent, specimen identity was included as a random intercept. The dependent variable in this analysis was ln-transformed increment size, modeled as a function of interval number (treated as a categorical predictor), species identity, ln-transformed SVL, and ln-transformed first-ring diameter. Sampling year was included in the model initially, and removed when unsupported. The models were fitted using lme4 (Bates et al., 2015 ). Inference was based on Satterthwaite/Kenward–Roger approximation (Kuznetsova et al., 2017 ), the software used was lmerTest . We calculated the marginal means and contrasts using emmeans (Lenth, 2023 ), and for data reshaping and manipulation we used tidyr and dplyr (Wickham et al., 2019 ). To evaluate post-maturation growth slowdown, we additionally examined model-based contrasts between intervals DIV2 and DIV3, which were represented by sufficient numbers of observations in both studied species. For reproductive traits, we used the original dataset of Barateli et al. ( 2022 ) from Saghamo and reanalyzed species differences in reproductive effort using Welch two-sample t-tests, Fisher’s exact tests for the fraction of females with low RE, and bootstrap comparison of lower quantiles. Population viability modeling We used a Leslie-matrix framework to explore how the observed differences in life-history parameters between Darevskia armeniaca and D. valentini could potentially affect population dynamics of these species. The purpose of this model was illustrative rather than predictive: it was designed to compare the demographic consequences of the observed differences in reproductive output and age structure between the two species under standardized assumptions. Age-specific transition schedules were parameterized to approximate the age distributions observed in field samples of adult females. Because direct survival estimates were not available, these transition values should be interpreted as heuristic demographic parameters chosen to reproduce the general empirical pattern of age frequencies rather than as direct estimates of annual survival. Fecundity values were based on average clutch size. For the sexual species, fecundity was halved to reflect the assumption of an approximately equal sex ratio. For D. armeniaca , fecundity was set from age 3 onward, with a mean value of 4 offspring per female. For D. valentini , fecundity was set to 1 at age 3 and to 2 from age 4 onward. Transition schedules were chosen so that the modeled age structure resembled the field data, in which females with 3 LAGs predominated in D. armeniaca , whereas females with 4 LAGs were more frequent than those with 3 LAGs in D. valentini . Population dynamics were simulated in annual time steps with both demographic and environmental stochasticity. Recruitment was generated as a Poisson process. Environmental stochasticity was introduced by allowing complete reproductive failure in some years, represented by multiplying fecundity by a Bernoulli variable with outcomes 0 or 1. Two reproductive-failure regimes were examined, assuming failure in 50% or 10% of years. Density dependence was incorporated by reducing effective fecundity as total population size approached a specified carrying capacity. Two carrying-capacity scenarios were considered, K = 100 and K = 1000. For each scenario, we ran 1000 replicate simulations from the same initial age vector. We summarized expected size of adult populations (age ≥ 3 years) over the first 50 years of simulation, calculated 95% confidence intervals for adult abundance at selected time points, estimated extinction times, and quantified long-term persistence probabilities. The model has been developed in R 4.5.2. The related script is presented in Appendix 1. Results Age Structure and cohort turnover The distribution of the age classes in the studied species is shown in Table 1 and Fig. 2 . Age structure differed significantly between the two species (cumulative link model: χ² = 5.58, df = 1, p = 0.018); the effect of year and the species × year interaction were not significant (χ² = 1.17, p = 0.28 and χ² = 1.19, p = 0.28, respectively), hence, D. armeniaca and D. valentini showed consistently different age distributions across years. Pairwise comparisons within each year did not show a significant difference between species in 2023 (Fisher’s exact test, p = 0.93), whereas the difference became significant in 2024 (p = 0.004), reflecting a higher proportion of younger females (3 LAGs) in D. armeniaca and a higher proportion of older females (5 LAGs) in D. valentini . Comparisons between years within each species did not reveal significant changes in age distribution ( D. armeniaca : p = 0.13; D. valentini : p = 0.71). As a contextual comparison, the proportion of the youngest adult females (≤ 3 LAGs, corresponding to the earliest reproductive age) was highest in D. mixta (0.615), intermediate in D. armeniaca (0.368), and lowest in D. valentini (0.188) (Fig. 3 ). Directional comparisons supported a higher proportion of these young adults in D. armeniaca than in D. valentini (z-test, p = 0.048; Fisher’s exact test, p = 0.079), and in D. mixta than in D. valentini (z-test, p = 0.003; Fisher’s exact test, p = 0.008). Because these comparisons are based on thresholded age classes from different localities, they are treated as descriptive rather than as part of the main inferential analysis. Body size and growth rates GLM showed a significant effect of species on the body size (SVL: p = 0.001), but the effect of either age or interaction between the species and age was insignificant (p > 0.12). D. valentini was significantly larger than D. armeniaca . Figure 4 shows SVL of five species of Darevskia , dependent on the number of recorded LAGs. Annual growth increments (DIVs) declined strongly with successive age intervals (linear mixed-effects model: interval effect, F5,118.9 = 34.36, p < 2×10 − 16). In contrast, neither species identity (F1,84.6 = 0.001, p = 0.973) nor the interaction between species and interval (F3,118.5 = 0.58, p = 0.63) had a significant effect on increment size. The sampling year did not improve model fit (χ2 = 0.98, p = 0.32) and was excluded from the final model. Model-based contrasts showed that increments declined significantly from interval 2 to interval 3 in both D. armeniaca and D. valentini (both p < 0.0001). However, the species did not differ significantly at interval 2 (p = 0.90) or interval 3 (p = 0.27), indicating similar rates of post-maturation growth slowdown in the two species. Descriptively, the distribution of the ratio DIV3/DIV2 suggested a broader upper tail in D. valentini , indicating that some individuals maintained relatively high post-maturation growth (Fig. 5 ). Still, this tendency was not supported as a significant species-level effect in the mixed-model analyses. Differences in the reproductive characteristics The original reproductive dataset of Barateli et al. ( 2022 ) from Saghamo confirmed that D. armeniaca and D. valentini did not differ significantly in average egg number per clutch, egg mass, or clutch mass. We then reanalyzed the same dataset to compare the distribution of reproductive effort (RE = clutch mass / female body mass). RE was significantly higher in D. armeniaca than in D. valentini (two-tailed t-test, p = 0.028). This difference suggested a higher fraction of females with relatively low reproductive effort in D. valentini (RE ≤ 0.25, 7/15 vs 4/18; Fisher’s exact test, p ≈ 0.036; odds ratio ≈ 4.81). A bootstrap comparison of the lower quartile of RE gave a similar result. Comparing the areas of occupancy The ranges of both D. armeniaca and D. valentini cover the upland treeless areas south of the Lesser Caucasus Mountains in southern Georgia, Armenia, and eastern Turkey (Fig. 1 a). Their ranges largely overlap. Simultaneously, long-term fieldwork showed that D. armeniaca has a substantially larger area of occupancy than D. valentini in southern Georgia (Fig. 6 ). D. armeniaca was recorded in 34 5×5 km squares across southern Georgia, whereas D. valentini was present in only 14 squares, all of which overlapped with the distribution of D. armeniaca . Another parthenogen, D. dahli , also has a broader area of occupancy than its patrilineal ancestor, D. portschinskii (Fig. 6 ). Modeling of metapopulation dynamics The simulation model suggested that during the first years of observation the parthenogens are expected to produce larger populations than the sexually breeding lizards. This pattern persisted for approximately the first 10 years of the simulations. Thereafter, the trend changed because extinction occurred more rapidly in the modeled parthenogenetic populations. In the current simulations, more than half of the parthenogenetic populations were lost after roughly 13–15 years, whereas in the sexual breeders this threshold was reached only after about 30–35 years. The median extinction time was 14 years in parthenogens and 34 years in sexual breeders. By year 100, no parthenogenetic populations survived, whereas about 11% of sexual populations were still present; by later time points, both categories had disappeared (Fig. 7 ). Discussion We can summarize our data as follows. Parthenogenetic D. armeniaca , sympatric and syntopic with its patrilineal ancestor, sexually reproducing D. valentini , tends to: (a) mature earlier (usually after three hibernations, as opposed to 4 hibernations in the sexual breeders); (b) live shorter (rarely survive after four hibernations). Growth deceleration after the third year did not differ significantly between the two species, although a subset of D. valentini females appeared to maintain relatively high post-maturation growth (Fig. 5 ). This pattern coincides with the lower reproductive effort of D. valentini females from the same population, compared with those of D. armeniaca (but based on different individuals; Barateli et al., 2022 ). These observed differences are consistent with higher population turnover in D. armeniaca and suggest that it may expand more rapidly across suitable habitats. The simplified model presented here suggests that the parthenogenetic population may grow faster and expand more intensively in neighboring locations than those of the sexual breeder with similar ecology. However, under unstable environmental conditions, the viability of parthenogenetic populations at the local level is lower than that of sexual breeders (Fig. 7 ). Such divergence between closely related, sympatric taxa is not unique to Darevskia and parallels life-history variation described in other lizard groups. In Agama , smaller-bodied species display r-like traits and produce larger clutches, whereas larger species invest in fewer, heavier offspring that enhance juvenile survival (Heideman, 1994 ). In Zootoka vivipara , high-altitude populations are strongly K-selected, with delayed maturity and low mortality, whereas lowland populations mature earlier and reproduce more frequently (Strijbosch & Creemers, 1988 ). Spinny lizard Sceloporus jarrovii matures earlier and reproduces opportunistically, whereas sympatric Sceloporus poinsetti matures later and reproduces more steadily (Ballinger 1973 ). These contrasts illustrate how environmental pressures shape life-history divergence and enable the coexistence of related lizard taxa. In the studied species of Darevskia , reproductive mode itself adds another important dimension to these life-history differences. Parthenogens and their sexual relatives diverge in life-history strategy within the same habitat, suggesting that demography and reproductive mode themselves act as major axes of ecological differentiation, given shared spatial and food resources. This demographic contrast is consistent with a colonization–persistence trade-off (Levins and Culver, 1971 ; Tilman, 1994 ; Hanski, 1999 ): parthenogens may colonize suitable habitats more rapidly, whereas sexual species may persist longer under variable conditions. To better understand how these demographic patterns relate to coexistence, we place them in the broader context of ecological niche differentiation observed in other lizard assemblages. In numerous studies of lizard community ecology (Pianka, 1973 ; Schoener, 1974 ; Losos, 1994 ; Pianka et al., 2017 ; Rubalcaba et al., 2023 ; Souza-Oliveira et al., 2024 ), the authors emphasize the niche differences and character displacement of coexisting lizards, assuming that the differences prevent interspecific competition and ensure long-lasting coexistence. In our system, there are indeed some differences in preferred climates and habitats between D. dahli and D. portschinskii , both on the macrogeographic (Tarkhnishvili et al., 2010 ; Petrosyan et al., 2020 ) and microhabitat (Barateli et al., 2021 ) scales. Specifically, D. dahli has a higher altitudinal limit than D. portschinskii , which is in line with the well-known phenomenon of geographic parthenogenesis (Vrijenhoek and Parker, 2009 ). When coexisting in the same location, D. portschinskii is more evenly distributed across the microhabitat and less dependent on proximity to water than D. dahli (Barateli et al., 2021 ). However, the overlap in the ranges of these two species is high, and despite negative interactions, they are commonly syntopic (Bakradze, 1977 ; Tarkhnishvili et al., 2010 ). Considering this broad overlap of suitable habitats, D. dahli occupies a larger part of a common suitable range than D. portschinskii (Fig. 6 ). There are no remarkable differences in the optimal habitats between D. armeniaca and D. valentini ; however, the extent of occurrence of D. armeniaca is broader (Fig. 6 ). This pattern of broad habitat overlap, yet wider occupancy by parthenogens, indicates that demographic differences may be more important than niche divergence in shaping this pattern. We hypothesize that the broader extent of occurrence and larger area of occupancy of parthenogenetic Darevskia compared to their paternal ancestors may result primarily from faster reproduction and more effective demographic expansion, rather than from intrinsic differences in ecological niche dimensions. The persistence of these differences through evolutionary time further supports this demographic explanation. The long-term coexistence of parthenogenetic and sexual Darevskia despite Pleistocene climatic oscillations supports this balance. Yanchukov et al. ( 2022 ) estimated the age of parthenogenetic Darevskia at over 0.5 Ma, indicating that neither lineage has replaced the other despite a limited genetic diversity of the parthenogenetic populations. The faster reproduction and expansion of the parthenogens at the metapopulation level appears to be the strategy that ensured their survival over multiple glacial cycles (Freitas et al., 2016 ; Tarkhnishvili et al., 2025). Simultaneously, the patrilineal ancestors of the parthenogens may persist longer under unfavorable conditions because of their longer reproductive lifespan. The analysis of reproductive effort, age distribution, and growth dynamics of D. valentini and D. armeniaca at Saghamo suggests that sexually breeding females may start reproducing only after the fourth hibernation, and that the reproductive effort of one-quarter of breeding females is low, as evidenced by the left-skewed distribution of RE. Simultaneously, in 20% of females from the same population, growth rates remained almost identical to those of the previous year. This pattern is consistent with the hypothesis that higher reproductive effort may be associated with more rapid growth deceleration and reduced adult persistence. When reproduction fails in one or more consecutive seasons (e.g., due to drought or winter mortality of eggs or hatchlings), sexually breeding species can persist through surviving adults that reproduce in later favorable years. In contrast, parthenogenetic species with their short lifespan and synchronous reproduction after the third hibernation face a higher risk of local extinction under the same conditions. These contrasting demographic strategies may help to explain the stable coexistence of the two reproductive modes across evolutionary timescales. The observed differences in age distribution, modal and highest recorded ages between parthenogens and their sexual ancestors suggest a simple explanation for their long-lasting coexistence. The commonly proposed view that sexual species persist mainly through higher genetic diversity may not fully explain their success. Instead, genetically determined longevity and repeated reproduction likely buffer sexual species during unfavorable periods, whereas parthenogens recover through colonization and rapid growth once conditions improve. Despite this overall framework, one important question remains open: what mechanisms underlie these demographic contrasts. The answer may relate to the maternal ancestry of D. armeniaca : D. mixta , a proven matrilineal ancestor (Murphy, 2000; Tarkhnishvili et al., 2020 ; Freitas, 2022), shows an age structure more similar to that of the parthenogen than to that of its paternal ancestors. Alternatively, the higher offspring number per individual in the parthenogen, resulting from the absence of males, may enhance population-level success through rapid reproduction. This feature, paralleled by lower individual variation in growth rates and low genetic variation, constrained their adaptive strategy to rapid reproduction rather than a longer lifespan. Together, these observations demonstrate that demographic and ecological differentiation is likely to maintain the long-lasting coexistence of ecologically similar parthenogenetic and sexually breeding lizards. Taken together, our findings suggest that Darevskia provides a rare natural example of long-term coexistence between unisexual and sexual lineages, .associated with contrasting life-history strategies and demographic tendencies that may contribute to long-term coexistence. Declarations ACKNOWLEDGEMENTS We are grateful to Prof. Mzia Zhvania (Institute of Chemical Biology, Ilia State University) and Dr. Nino Pochkidze (Chemical Biology, Ilia State University) for generously providing access to the microtome facilities. We are especially thankful to Dr. Pochkidze, who introduced us to the use of the microtome and supported us with all the necessary materials during the first days of this work. We also thank the bachelor's degree students (Mariam Mamaladze, Maiam Sabiashvili, David Mamagulashvili, Natali Bordzikuli, Saba Nozadze) who assisted with the skeletochronology preparations, including cleaning the bones and sectioning them with the microtome. Finally, we thank Armen Seropian for his valuable suggestions and constant support throughout this study. Funding. This study was conducted with the support of the Shota Rustaveli National Science Foundation under project FR-23-17324. Conflicts of interest. No conflict of interest to declare. Ethics approval. All animals were released at the capture site after sampling. No animals were euthanized. The ethics commission of Ilia State University reviewed the methodology and study protocols and approved this research, permit #1018. No permits were required for the field study of the Darevskia species in Georgia. Consent to participate. Not applicable Consent to publication. Not applicable Availability of data and material. All datasets are included in the supplementary materials for online publication. Code availability . The population model included in the supplementary materials in shape of Excel spreadsheet. Authors' contributions. Study design: NB, DT (equal); field work: NB, GI (equal). Laboratory procedures: NB (leading), GI (supporting); Data analysis: DT, NB (equal); writing: NB, DT (equal). References Arakelyan MS, Danielyan FD (2000) Growth and age composition of some parthenogenetic and bisexual species of Armenian rock lizards (Lacerta). Entomol Rev 80(1):S161 Arakelyan M, Spangenberg V, Petrosyan V, Ryskov A, Kolomiets O, Galoyan E (2023) Evolution of parthenogenetic reproduction in Caucasian rock lizards: a review. Curr Zool 69:128–135. ttps://doi.org/10.1093/cz/zoac036 Avise JC (2015) Evolutionary perspectives on clonal reproduction in vertebrate animals. 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Supplementary Files Appendixesforonlinepublication.docx Appendix1.txt TableS1.csv Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 16 May, 2026 Reviews received at journal 15 May, 2026 Reviews received at journal 11 Apr, 2026 Reviewers agreed at journal 30 Mar, 2026 Reviewers agreed at journal 25 Mar, 2026 Reviewers invited by journal 25 Mar, 2026 Editor assigned by journal 17 Mar, 2026 Submission checks completed at journal 17 Mar, 2026 First submitted to journal 15 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9127021","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":612264473,"identity":"850d26e0-f8d5-46bc-85bd-419ead58356a","order_by":0,"name":"Natia Barateli","email":"","orcid":"","institution":"Leibniz Caucasus Biodiversity Research Center, Ilia State University","correspondingAuthor":false,"prefix":"","firstName":"Natia","middleName":"","lastName":"Barateli","suffix":""},{"id":612264474,"identity":"f358ea91-90c8-4e3e-96de-b09ad51640c7","order_by":1,"name":"David Tarkhnishvili","email":"data:image/png;base64,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","orcid":"","institution":"Leibniz Caucasus Biodiversity Research Center, Ilia State University","correspondingAuthor":true,"prefix":"","firstName":"David","middleName":"","lastName":"Tarkhnishvili","suffix":""},{"id":612264475,"identity":"59584951-e4f0-4d30-abed-81962e6b3bd9","order_by":2,"name":"Giorgi Iankoshvili","email":"","orcid":"","institution":"Leibniz Caucasus Biodiversity Research Center, Ilia State University","correspondingAuthor":false,"prefix":"","firstName":"Giorgi","middleName":"","lastName":"Iankoshvili","suffix":""}],"badges":[],"createdAt":"2026-03-15 07:53:34","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9127021/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9127021/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105567106,"identity":"63507682-a5aa-4421-9a13-e182781fde45","added_by":"auto","created_at":"2026-03-27 12:58:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":925607,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of the studied species and origin of the parthenogens. (a) finding locations of two parthenogenetic lineages (\u003cem\u003eD. armeniaca, D. dahli\u003c/em\u003e), their patrilineal (\u003cem\u003eD. valentini, D. portschinskii\u003c/em\u003e) and matrilineal (\u003cem\u003eD. mixta\u003c/em\u003e) ancestors in the Caucasus ecoregion (after: Tarkhnishvili and Iankoshvili, 2023; Tarkhnishvili et al., 2010, 2020, 2025). Sampling locations shown with larger circles. (b) the origin of the hybrid parthenogenetic forms used in this study (after Murphy et al, 2000); the arrows show maternal (\u003cem\u003eD. mixta \u003c/em\u003e) and paternal (\u003cem\u003eD. portschinskii, D. valentini\u003c/em\u003e) ancestry of parthenogenetic \u003cem\u003eD. armeniaca \u003c/em\u003eand \u003cem\u003eD. dahli\u003c/em\u003e. (c) sampling locations.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/83bc896a177fadbf75def00d.png"},{"id":105548612,"identity":"4005e420-596f-47af-86ba-d7f7c3993e1d","added_by":"auto","created_at":"2026-03-27 09:34:03","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":477584,"visible":true,"origin":"","legend":"\u003cp\u003etransverse cross-section of the femoral diaphysis used for skeletochronological age estimation. (a) \u003cem\u003eDarevskia armeniaca\u003c/em\u003e, estimated age 3 years; (b) \u003cem\u003eD. valentini\u003c/em\u003e, estimated age 4 years. Arrows indicate lines of arrested growth (LAGs); RL denotes the endosteal resorption line. A closely spaced double line adjacent to the innermost LAG in \u003cem\u003eD. valentini\u003c/em\u003e is interpreted as an intra-annual mark and was not counted as an additional year.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/6e73921deb41f3b5e2352e25.png"},{"id":105567085,"identity":"ae763cc3-a46c-4db7-a985-c81aba5718a4","added_by":"auto","created_at":"2026-03-27 12:58:16","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":328611,"visible":true,"origin":"","legend":"\u003cp\u003eThe proportions of age classes (2 to 6 LAGs) in the studied \u003cem\u003eDarevskia armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/34e3d7a954864d946bfe7d59.png"},{"id":105548609,"identity":"ff747dd1-0473-44d0-8431-5d79c41920c6","added_by":"auto","created_at":"2026-03-27 09:34:03","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":168051,"visible":true,"origin":"","legend":"\u003cp\u003e75% Boxplots showing snout-vent length (SVL, cm) of the five lizard species from this study.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/93740dc54abf0e4bd999749f.png"},{"id":105548606,"identity":"6995af31-5259-4e41-98ee-bfb841e1a0a5","added_by":"auto","created_at":"2026-03-27 09:34:02","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":252234,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of the ratio DIV3/DIV2 in \u003cem\u003eD. armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e. This ratio provides a descriptive index of post-maturation growth slowdown, with higher values indicating weaker decline from the second to the third annual growth increment. The broader upper tail in \u003cem\u003eD. valentini\u003c/em\u003e reflects the presence of some individuals maintaining relatively high post-maturation growth.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/33bbd0a77c3aa73f4598ad1a.png"},{"id":105548605,"identity":"f361c067-c904-48df-a042-275a2d6dab97","added_by":"auto","created_at":"2026-03-27 09:34:02","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":731948,"visible":true,"origin":"","legend":"\u003cp\u003eThe distribution of the recorded locations of the two parthenogenetic \u003cem\u003eDarevskia \u003c/em\u003eand their paternal ancestors in Georgia. \u003cstrong\u003e(a)\u003c/strong\u003e \u003cem\u003eD. armeniaca\u003c/em\u003e and its sexual ancestor \u003cem\u003eD. valentini\u003c/em\u003e. \u003cstrong\u003e(b)\u003c/strong\u003e \u003cem\u003eD. dahli\u003c/em\u003e and its sexual ancestor \u003cem\u003eD. portschinskii\u003c/em\u003e. Blue squares: both the parthenogen and its ancestral species present; yellow squares - only the parthenogen present; orange squares - only the bisexual species present. Dots within the squares indicate documented locations of the lizards.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/ffa592a0e7b612ee38c68ed2.png"},{"id":105566768,"identity":"541f0aa0-c358-4dd6-9804-d0868f9629c6","added_by":"auto","created_at":"2026-03-27 12:57:16","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":763231,"visible":true,"origin":"","legend":"\u003cp\u003eStochastic simulations comparing number dynamics and population persistence of parthenogenetic and sexually reproducing lizards. Left panels indicate adult population size during 50 years, and shaded areas indicate 95% confidence intervals across 1,000 replicate simulations. Right panels show long-term population persistence probability; shaded areas also indicate 95% confidence intervals. The upper two rows correspond to K = 100, and the lower two rows to K = 1000; within each pair, simulations assume either 50% or 90% successful reproductive years, as indicated in the panels. Solid lines represent the parthenogenetic species and dashed lines the sexually reproducing species. In all panels, adult population size refers to individuals aged 3 years or older; the x-axis in the persistence plots (right) is shown on a logarithmic scale.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/385c8dfd05889088dd8f7d66.png"},{"id":105728222,"identity":"8462ca58-4180-45d2-8f88-0dfda70b6cc1","added_by":"auto","created_at":"2026-03-30 11:10:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4524620,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/85d26577-8825-4d58-948b-1efcf9edbac3.pdf"},{"id":105548602,"identity":"9de838f3-46a2-4604-bc20-7ccd990acb30","added_by":"auto","created_at":"2026-03-27 09:34:02","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":15322,"visible":true,"origin":"","legend":"","description":"","filename":"Appendixesforonlinepublication.docx","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/6585b2734fa2df116e390bce.docx"},{"id":105567450,"identity":"59571715-a2c4-45e2-b796-9276ebb366c7","added_by":"auto","created_at":"2026-03-27 12:59:44","extension":"txt","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":13198,"visible":true,"origin":"","legend":"","description":"","filename":"Appendix1.txt","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/e558c1b429ae3823c21a8920.txt"},{"id":105548604,"identity":"4b0ff02f-185a-48d2-8b3a-3b35f3ed71af","added_by":"auto","created_at":"2026-03-27 09:34:02","extension":"csv","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":9117,"visible":true,"origin":"","legend":"","description":"","filename":"TableS1.csv","url":"https://assets-eu.researchsquare.com/files/rs-9127021/v1/aaa358bdf3300092076d4366.csv"}],"financialInterests":"No competing interests reported.","formattedTitle":"Trade-off between local persistence and rapid expansion: a case study of a parthenogenetic lizard species and its sexually reproducing ancestor","fulltext":[{"header":"Introduction","content":"\u003cp\u003eParthenogenetic lineages often differ in key life-history traits from closely related sexual breeders. Usually, they have shorter generations, start reproducing at a younger age, and have higher intrinsic rates of population increase (r) (Maynard Smith, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1978\u003c/span\u003e). Such patterns have been reported for many short-lived, asexual or facultative parthenogenetic invertebrates, including aphids and some rotifers (Hughes, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1963\u003c/span\u003e; Williams, \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e1975\u003c/span\u003e; Bell, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1982\u003c/span\u003e). Rather than increasing lifespan or the total number of reproductive seasons, both obligate and cyclical parthenogens invest proportionally more in early and rapid reproduction, a strategy that may enhance short-term population growth and facilitate rapid spatial expansion (Cuellar, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1977\u003c/span\u003e; Vrijenhoek, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Doroszuk et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Stelzer, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Roark \u0026amp; Bjorndal, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). These observations are consistent with theoretical expectations that asexual reproduction may be associated with rapid demographic responses under stable, optimal conditions, whereas sexual reproduction is more often associated with slower population growth but greater long-term evolutionary adaptability in changing environments (Williams, \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e1975\u003c/span\u003e; Maynard Smith, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1978\u003c/span\u003e; Cuellar, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1977\u003c/span\u003e; Bell, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Otto, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn vertebrates, and particularly in parthenogenetic lizards, the relationship between reproductive mode and life-history traits appears to be more complex. Vertebrates are characterized by longer lifespans, delayed maturation, and repeated reproductive seasons, which may decouple short-term reproductive output from lifetime fitness. Consequently, the demographic effects of parthenogenesis in vertebrates are expected to depend on complex trade-offs among age at maturity, fecundity, survival, and reproductive longevity. Empirical studies of parthenogenetic lizards illustrate this complexity. Wright and Lowe (\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1968\u003c/span\u003e) showed that parthenogenetic \u003cem\u003eAspidoscelis tesselata\u003c/em\u003e start reproducing earlier in life than the related bisexual species \u003cem\u003eA. sexlineata\u003c/em\u003e under similar environmental conditions. However, \u003cem\u003eA. tesselata\u003c/em\u003e reaches maturity at a smaller body size (and presumably earlier age) and produces smaller clutches. This example illustrates that differences in reproductive mode may involve compensating changes among life-history components (e.g., earlier maturation versus clutch size), and the resulting lifetime reproductive output may depend on additional factors such as clutch frequency and longevity.\u003c/p\u003e \u003cp\u003eA triploid parthenogen, \u003cem\u003eA. neotesselata\u003c/em\u003e, exhibits clutch sizes comparable to its sexual ancestor, \u003cem\u003eA. patrilineata\u003c/em\u003e, differing from its diploid parthenogenetic predecessor \u003cem\u003eA. tesselata\u003c/em\u003e (Taylor et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Kearney and Shine (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) demonstrated that parthenogenetic geckos of the \u003cem\u003eHeteronotia binoei\u003c/em\u003e complex have smaller clutch sizes than their sexually reproducing relatives, suggesting that earlier reproduction does not necessarily translate into greater reproductive output, because different components of life history may change in compensatory ways. Taken together, these findings indicate that lizard parthenogens and their sexual relatives cannot be simply placed at opposite ends of a simple r\u0026ndash;K continuum (sensu Pianka, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1970\u003c/span\u003e; Roff, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1992\u003c/span\u003e). Instead, differences between reproductive modes may be better described with a multidimensional life-history framework involving trade-offs among traits such as age at maturity, generation time, survival dynamics, reproductive lifespan or senescence, egg size, clutch size, and clutch frequency.\u003c/p\u003e \u003cp\u003eCaucasian rock lizards of the genus \u003cem\u003eDarevskia\u003c/em\u003e represent one of the best-studied vertebrate systems comprising multiple sexually reproducing species and several parthenogenetic lineages of hybrid origin (Darevsky, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Murphy, 2000; Tarkhnishvili et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Freitas et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Yanchukov et al., \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Parthenogenetic species of this genus commonly coexist with their patrilineal ancestors, i.e., the paternal sexual species involved in their hybrid origin (Darevsky, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Danielyan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Tarkhnishvili et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Barateli et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Arakelyan et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Galoyan et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). In southern Georgia, two parthenogenetic species (\u003cem\u003eDarevskia armeniaca\u003c/em\u003e and \u003cem\u003eD. dahli\u003c/em\u003e) share habitats with their paternal sexual ancestors (\u003cem\u003eD. valentini\u003c/em\u003e and \u003cem\u003eD. portschinskii\u003c/em\u003e, respectively). This system therefore provides an opportunity to compare life-history traits between parthenogenetic lineages and their sexual progenitors under broadly comparable environmental conditions. Both parthenogenetic species share the same matrilineal ancestor, \u003cem\u003eD. mixta\u003c/em\u003e. Although geographically close to the ranges of the studied species, \u003cem\u003eD. mixta\u003c/em\u003e does not overlap spatially with either the parthenogenetic lineages or their paternal ancestors.\u003c/p\u003e \u003cp\u003eA previous study (Barateli et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) revealed different patterns of divergence in reproductive traits between the parthenogen and its patrilineal ancestor. \u003cem\u003eD. armeniaca\u003c/em\u003e exhibited significantly higher reproductive effort (clutch mass relative to female body mass) than \u003cem\u003eD. valentini\u003c/em\u003e, while egg size did not differ between the species. This finding led to the hypothesis that increased reproductive effort may reduce adult female survival to subsequent breeding seasons, whereas larger egg size may enhance juvenile survival; however, these hypotheses remain largely untested. Such trade-offs between current reproductive investment, growth, and survival is central to life-history theory (Stearns, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Roff, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1992\u003c/span\u003e) and may shape differences in demographic strategy between parthenogenetic and sexual lineages.\u003c/p\u003e \u003cp\u003eIn this study, we focus primarily on the sympatric species pair consisting of the parthenogenetic \u003cem\u003eDarevskia armeniaca\u003c/em\u003e and its bisexual paternal ancestor \u003cem\u003eD. valentini\u003c/em\u003e, co-occurring at the same site in southern Georgia (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). All main statistical analyses are centered on this sympatric system. Other taxa, including the matrilineal ancestor of the parthenogen, \u003cem\u003eD. mixta\u003c/em\u003e, and another pair of parthenogenetic species and its patrilineal ancestor, namely \u003cem\u003eD. dahli\u003c/em\u003e and \u003cem\u003eD. portschinskii\u003c/em\u003e, are used only for contextual comparison. We restricted most analyses to adult females from populations occupying the same habitat. With this approach, we aimed to minimize environmental confounding and isolate species-level differences in life-history traits.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUsing skeletochronological data, we compared age structure and growth patterns of these species to test whether parthenogenetic \u003cem\u003eD. armeniaca\u003c/em\u003e exhibits demographic traits consistent with a faster life-history pace relative to its bisexual ancestor. Specifically, we hypothesize that, in sympatry, \u003cem\u003eD. armeniaca\u003c/em\u003e will show (1) earlier age at maturity, (2) shorter generation time and shorter lifespan, and (3) initially rapid but more strongly decelerating growth compared to females of the patrilineal species \u003cem\u003eD. valentini\u003c/em\u003e. By analyzing the relative distribution patterns of the two species, we assess whether these differences in life history may influence the spatial distribution of the parthenogen and its paternal ancestor. We also use simple demographic simulations to illustrate how observed life-history differences may translate into contrasting short-term population trajectories.\u003c/p\u003e "},{"header":"Materials and Methods","content":"\u003ch3\u003eStudy system and sampling design\u003c/h3\u003e\n\u003cp\u003eThis study focuses on a location from the surroundings of Saghamo Lake (from here onwards “Saghamo”, ~ 2000 m a.s.l. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) where \u003cem\u003eD. armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e occur sympatrically and syntopically. The two species were observed at broadly similar frequencies during field observations in 2025: from 154 individuals observed and photographed, \u003cem\u003eD. armeniaca\u003c/em\u003e was 49.3%, females of \u003cem\u003eD. valentini\u003c/em\u003e 31.2%, and males of \u003cem\u003eD. valentini\u003c/em\u003e − 19.5%.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003ctable id=\"Tab1\" border=\"1\"\u003e \u003ccaption\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSample locations and sample sizes (see also Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). TC- Total Count of Samples; SCY - Sample Count by Years. Only reproductive females were sampled.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003c/colgroup\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" rowspan=\"2\"\u003e \u003cp\u003eSpecies\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eLat °N)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eLong (°E)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003em a.s.l.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eTC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\"\u003e \u003cp\u003eSCY\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003e2025\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cem\u003eD. armeniaca\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003eSaghamo Lake\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e41.29°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e43.73°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e2015\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cem\u003eD. armeniaca\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003eKirkhbulakhi\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e41.23°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e43.28°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1715\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cem\u003eD. dahli\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003eKojori\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e41.64°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e44.68°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cem\u003eD. mixta\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003eBakuriani\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e41.79°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e43.47°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1281\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cem\u003eD. portschinskii\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003eKojori\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e41.64°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e44.68°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cem\u003eD. portschinskii\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003eTana\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e41.84°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e43.85°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1358\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cem\u003eD. valentini\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003eSaghamo Lake\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e41.29°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e43.73°\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e2015\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/table\u003e\u003c/div\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003eField sampling was conducted during the reproductive season (May-June) in 2023–2025. Adult females were captured by hand. Sample sizes are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. We concentrated on adult gravid females, identified by manual palpation of the abdomen; individuals were confirmed as gravid by the presence of detectable eggs.\u003c/p\u003e \u003cp\u003eObservations from another species pair, parthenogenetic \u003cem\u003eD. dahli\u003c/em\u003e and its paternal ancestor \u003cem\u003eD. portschinskii\u003c/em\u003e that also coexist in Georgia, were not included in statistical analyses because the sample size of the sexual species (\u003cem\u003eD. portschinskii\u003c/em\u003e) was too small for reliable comparison. These data are therefore presented only descriptively in the supplementary material, and used for illustrating the differences in body size and geographic distribution. Notably, field observations suggest that \u003cem\u003eD. dahli\u003c/em\u003e may locally reach higher densities than its sexual ancestor \u003cem\u003eD. portschinskii\u003c/em\u003e in areas where the two species coexist (Tarkhnishvili et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e), although the limited sample size in the present dataset does not allow us to evaluate this pattern quantitatively.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMorphological measurements and tissue sampling\u003c/h2\u003e \u003cp\u003eFor each individual, snout–vent length (SVL) was measured to the nearest 0.1 mm using digital calipers. Sex was determined based on secondary sexual characteristics (presence of hemipenes and enlarged femoral pores).\u003c/p\u003e \u003cp\u003eThe fourth phalanx of the right lower toe was clipped from each live individual, as recommended by Castanet \u0026amp; Smirina (\u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e); Beaupre et al. (\u003cspan class=\"CitationRef\"\u003e2004\u003c/span\u003e). The diameter of the 4th phalanx in these lizards varies between 0.3–0.8 mm and clipping never causes bleeding. Most of the animals were released at the capture site immediately after sampling. Five females of each species were transported to the lab and kept captive before being released. None of them showed any sign of inflammation. Each individual was sampled only once; individuals were not marked or recaptured.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSkeletochronology and age estimation\u003c/h3\u003e\n\u003cp\u003eSkeletochronology is widely regarded as the most reliable method for age determination in reptiles (Guarino \u0026amp; Mezzasalma, \u003cspan class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAge was estimated using skeletochronology following standard protocols used for inferring age in reptiles (Castanet and Smirina, \u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e; Arakelyan \u0026amp; Danielyan, \u003cspan class=\"CitationRef\"\u003e2000\u003c/span\u003el et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePhalanges were decalcified in 5% nitric acid (40 min for small-bodied species and up to 1 h for larger-bodied species), rinsed in tap water for more than 12 h, and sectioned at 18–20 µm thickness using a freezing microtome. Sections were stained with Ehrlich’s hematoxylin (20 min), mounted in glycerin, and sealed with a coverslip. Digital images were obtained under a light microscope equipped with a digital camera. Lines of arrested growth (LAGs; concentric rings formed in bone tissue during seasonal pauses in growth during hibernation) were counted on transverse sections of the diaphysis. Because one LAG is generally formed per year, the number of LAGs provides an estimate of individual age. Only clearly visible, continuous lines were considered annual growth marks. Faded or discontinuous rings were excluded, and double lines were interpreted as a single annual growth cycle following established criteria (Castanet and Smirina, \u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e). Representative cross-sections are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGrowth dynamics were inferred from inter-annuli distances (DIVs), defined as the distances between successive LAGs. DIVs represent annual growth increments and therefore provide an estimate of somatic growth achieved during each year of life, and serve for analyses of growth rates and growth deceleration across age classes and species. All individual-level morphometric and skeletochronological data for \u003cem\u003eD. armeniaca, D. valentini, D. mixta, D. dahli\u003c/em\u003e, and \u003cem\u003eD. portschinskii\u003c/em\u003e are provided in Supplementary Data (Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). To assess age structure, we compared the relative frequencies of individuals with different numbers of LAGs across species.\u003c/p\u003e\n\u003ch3\u003eReproduction\u003c/h3\u003e\n\u003cp\u003eReproductive traits analyzed in this study were based on the dataset published in Barateli et al. (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e), collected from the same populations as the present skeletochronological samples, although from different individuals. In that study, gravid females were temporarily maintained in small tanks until oviposition, freshly deposited eggs were measured and weighed, and females and hatchlings were subsequently released at their site of capture. The variables used here were egg size, clutch size, clutch mass, and reproductive effort (RE), defined as clutch mass divided by female body mass prior to oviposition. No new reproductive data were collected for the present study. Instead, we used the original dataset of Barateli et al. (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) and, where relevant, reanalyzed it to compare distributions of reproductive effort between species from Saghamo. No additional published reproductive datasets were used.\u003c/p\u003e\n\u003ch3\u003eMapping the ranges\u003c/h3\u003e\n\u003cp\u003eTo evaluate whether differences in life-history traits between parthenogenetic species and their sexual ancestors are associated with differences in spatial distribution, we compared the proportion of occupied grid cells within each species' extent of occurrence (EOO). Occurrence records compiled from previous publications (Darevsky, \u003cspan class=\"CitationRef\"\u003e1967\u003c/span\u003e; Tarkhnishvili et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2013\u003c/span\u003e; Tarkhnishvili \u0026amp; Iankoshvili, \u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e) were plotted on a 5 × 5 km grid. We separated the squares where both species of the pair, only the parthenogen or the paternal ancestor, were found. For mapping, we used QGIS software (QGIS Development Team, version 3.34, 2024). For contextual comparison, analogous occupancy map is also shown for \u003cem\u003eD. dahli\u003c/em\u003e and \u003cem\u003eD. portschinskii\u003c/em\u003e.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003e(1) We compared age distributions between species and years using cumulative link models, treating the number of LAGs as an ordered response variable. Species, year, and interaction between species*year were used as predictors. The frequencies of each age class were used as weights in the model. This approach allowed all age classes to be analyzed simultaneously. Because some age classes were rare, contingency-table tests based on Fisher’s exact test with Monte-Carlo simulation (10,000 replicates) were additionally used to compare species-specific age distributions within each year and to test year-to-year changes within each species. As a secondary descriptive comparison, we also summarized the proportion of the youngest adult females (≤ 3 LAGs), corresponding to the earliest reproductive age, in \u003cem\u003eD. armeniaca\u003c/em\u003e, \u003cem\u003eD. valentini\u003c/em\u003e, and \u003cem\u003eD. mixta\u003c/em\u003e. These comparisons were used only to illustrate broad differences in age structure and were evaluated with directional z-tests and Fisher’s exact tests. All analyses were performed in R 4.5.2 (packages \u003cem\u003eordinal, dplyr, tidyr, ggplot2\u003c/em\u003e).\u003c/p\u003e \u003cp\u003e(2) We compared adult female body length (SVL) among the species (five species included – \u003cem\u003eD. armeniaca\u003c/em\u003e with its parental species, \u003cem\u003eD. dahli\u003c/em\u003e, and \u003cem\u003eD. portschinskii\u003c/em\u003e) and age classes (\u003cem\u003eD. armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e) using General Linear Model (species and age/ LAGs number used as predictors) and, where appropriate, the Welch two-sample t-test. Because adult SVL is the cumulative outcome of growth over multiple years, these analyses were used to assess whether age structure and growth patterns were reflected in final adult size.\u003c/p\u003e \u003cp\u003e(3) We analyzed annual growth increments (DIV1–DIV6) using linear mixed-effects models in R 4.5.2. Each individual contributed several measurements corresponding to successive inter-LAG distances recorded from the same phalanx section; because these increments originate from the same individual and are therefore not statistically independent, specimen identity was included as a random intercept. The dependent variable in this analysis was ln-transformed increment size, modeled as a function of interval number (treated as a categorical predictor), species identity, ln-transformed SVL, and ln-transformed first-ring diameter. Sampling year was included in the model initially, and removed when unsupported. The models were fitted using \u003cem\u003elme4\u003c/em\u003e (Bates et al., \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e). Inference was based on Satterthwaite/Kenward–Roger approximation (Kuznetsova et al., \u003cspan class=\"CitationRef\"\u003e2017\u003c/span\u003e), the software used was \u003cem\u003elmerTest\u003c/em\u003e. We calculated the marginal means and contrasts using \u003cem\u003eemmeans\u003c/em\u003e (Lenth, \u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e), and for data reshaping and manipulation we used \u003cem\u003etidyr\u003c/em\u003e and \u003cem\u003edplyr\u003c/em\u003e (Wickham et al., \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e). To evaluate post-maturation growth slowdown, we additionally examined model-based contrasts between intervals DIV2 and DIV3, which were represented by sufficient numbers of observations in both studied species.\u003c/p\u003e \u003cp\u003eFor reproductive traits, we used the original dataset of Barateli et al. (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) from Saghamo and reanalyzed species differences in reproductive effort using Welch two-sample t-tests, Fisher’s exact tests for the fraction of females with low RE, and bootstrap comparison of lower quantiles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003ePopulation viability modeling\u003c/h2\u003e \u003cp\u003eWe used a Leslie-matrix framework to explore how the observed differences in life-history parameters between \u003cem\u003eDarevskia armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e could potentially affect population dynamics of these species. The purpose of this model was illustrative rather than predictive: it was designed to compare the demographic consequences of the observed differences in reproductive output and age structure between the two species under standardized assumptions.\u003c/p\u003e \u003cp\u003eAge-specific transition schedules were parameterized to approximate the age distributions observed in field samples of adult females. Because direct survival estimates were not available, these transition values should be interpreted as heuristic demographic parameters chosen to reproduce the general empirical pattern of age frequencies rather than as direct estimates of annual survival. Fecundity values were based on average clutch size. For the sexual species, fecundity was halved to reflect the assumption of an approximately equal sex ratio.\u003c/p\u003e \u003cp\u003eFor \u003cem\u003eD. armeniaca\u003c/em\u003e, fecundity was set from age 3 onward, with a mean value of 4 offspring per female. For \u003cem\u003eD. valentini\u003c/em\u003e, fecundity was set to 1 at age 3 and to 2 from age 4 onward. Transition schedules were chosen so that the modeled age structure resembled the field data, in which females with 3 LAGs predominated in \u003cem\u003eD. armeniaca\u003c/em\u003e, whereas females with 4 LAGs were more frequent than those with 3 LAGs in \u003cem\u003eD. valentini\u003c/em\u003e.\u003c/p\u003e \u003cp\u003ePopulation dynamics were simulated in annual time steps with both demographic and environmental stochasticity. Recruitment was generated as a Poisson process. Environmental stochasticity was introduced by allowing complete reproductive failure in some years, represented by multiplying fecundity by a Bernoulli variable with outcomes 0 or 1. Two reproductive-failure regimes were examined, assuming failure in 50% or 10% of years. Density dependence was incorporated by reducing effective fecundity as total population size approached a specified carrying capacity. Two carrying-capacity scenarios were considered, K = 100 and K = 1000.\u003c/p\u003e \u003cp\u003eFor each scenario, we ran 1000 replicate simulations from the same initial age vector. We summarized expected size of adult populations (age ≥ 3 years) over the first 50 years of simulation, calculated 95% confidence intervals for adult abundance at selected time points, estimated extinction times, and quantified long-term persistence probabilities.\u003c/p\u003e \u003cp\u003eThe model has been developed in R 4.5.2. The related script is presented in Appendix 1.\u003c/p\u003e \u003c/div\u003e\n"},{"header":"Results","content":"\u003ch3\u003eAge Structure and cohort turnover\u003c/h3\u003e\u003cp\u003eThe distribution of the age classes in the studied species is shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eAge structure differed significantly between the two species (cumulative link model: χ² = 5.58, df = 1, p = 0.018); the effect of year and the species × year interaction were not significant (χ² = 1.17, p = 0.28 and χ² = 1.19, p = 0.28, respectively), hence, \u003cem\u003eD. armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e showed consistently different age distributions across years.\u003c/p\u003e\u003cp\u003ePairwise comparisons within each year did not show a significant difference between species in 2023 (Fisher’s exact test, p = 0.93), whereas the difference became significant in 2024 (p = 0.004), reflecting a higher proportion of younger females (3 LAGs) in \u003cem\u003eD. armeniaca\u003c/em\u003e and a higher proportion of older females (5 LAGs) in \u003cem\u003eD. valentini\u003c/em\u003e.\u003c/p\u003e\u003cp\u003eComparisons between years within each species did not reveal significant changes in age distribution (\u003cem\u003eD. armeniaca\u003c/em\u003e: p = 0.13; \u003cem\u003eD. valentini\u003c/em\u003e: p = 0.71).\u003c/p\u003e\u003cp\u003eAs a contextual comparison, the proportion of the youngest adult females (≤ 3 LAGs, corresponding to the earliest reproductive age) was highest in \u003cem\u003eD. mixta\u003c/em\u003e (0.615), intermediate in \u003cem\u003eD. armeniaca\u003c/em\u003e (0.368), and lowest in \u003cem\u003eD. valentini\u003c/em\u003e (0.188) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). Directional comparisons supported a higher proportion of these young adults in \u003cem\u003eD. armeniaca\u003c/em\u003e than in \u003cem\u003eD. valentini\u003c/em\u003e (z-test, p = 0.048; Fisher’s exact test, p = 0.079), and in \u003cem\u003eD. mixta\u003c/em\u003e than in \u003cem\u003eD. valentini\u003c/em\u003e (z-test, p = 0.003; Fisher’s exact test, p = 0.008). Because these comparisons are based on thresholded age classes from different localities, they are treated as descriptive rather than as part of the main inferential analysis.\u003c/p\u003e\u003ch3\u003eBody size and growth rates\u003c/h3\u003e\u003cp\u003eGLM showed a significant effect of species on the body size (SVL: p = 0.001), but the effect of either age or interaction between the species and age was insignificant (p \u0026gt; 0.12). \u003cem\u003eD. valentini\u003c/em\u003e was significantly larger than \u003cem\u003eD. armeniaca\u003c/em\u003e. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e shows SVL of five species of \u003cem\u003eDarevskia\u003c/em\u003e, dependent on the number of recorded LAGs.\u003c/p\u003e\u003cp\u003eAnnual growth increments (DIVs) declined strongly with successive age intervals (linear mixed-effects model: interval effect, F5,118.9 = 34.36, p \u0026lt; 2×10 − 16). In contrast, neither species identity (F1,84.6 = 0.001, p = 0.973) nor the interaction between species and interval (F3,118.5 = 0.58, p = 0.63) had a significant effect on increment size. The sampling year did not improve model fit (χ2 = 0.98, p = 0.32) and was excluded from the final model.\u003c/p\u003e\u003cp\u003eModel-based contrasts showed that increments declined significantly from interval 2 to interval 3 in both \u003cem\u003eD. armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e (both p \u0026lt; 0.0001). However, the species did not differ significantly at interval 2 (p = 0.90) or interval 3 (p = 0.27), indicating similar rates of post-maturation growth slowdown in the two species.\u003c/p\u003e\u003cp\u003eDescriptively, the distribution of the ratio DIV3/DIV2 suggested a broader upper tail in \u003cem\u003eD. valentini\u003c/em\u003e, indicating that some individuals maintained relatively high post-maturation growth (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). Still, this tendency was not supported as a significant species-level effect in the mixed-model analyses.\u003c/p\u003e\u003ch2\u003eDifferences in the reproductive characteristics\u003c/h2\u003e\u003cp\u003eThe original reproductive dataset of Barateli et al. (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) from Saghamo confirmed that \u003cem\u003eD. armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e did not differ significantly in average egg number per clutch, egg mass, or clutch mass. We then reanalyzed the same dataset to compare the distribution of reproductive effort (RE = clutch mass / female body mass). RE was significantly higher in \u003cem\u003eD. armeniaca\u003c/em\u003e than in \u003cem\u003eD. valentini\u003c/em\u003e (two-tailed t-test, p = 0.028). This difference suggested a higher fraction of females with relatively low reproductive effort in \u003cem\u003eD. valentini\u003c/em\u003e (RE ≤ 0.25, 7/15 vs 4/18; Fisher’s exact test, p ≈ 0.036; odds ratio ≈ 4.81). A bootstrap comparison of the lower quartile of RE gave a similar result.\u003c/p\u003e\u003ch2\u003eComparing the areas of occupancy\u003c/h2\u003e\u003cp\u003eThe ranges of both \u003cem\u003eD. armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e cover the upland treeless areas south of the Lesser Caucasus Mountains in southern Georgia, Armenia, and eastern Turkey (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea). Their ranges largely overlap. Simultaneously, long-term fieldwork showed that \u003cem\u003eD. armeniaca\u003c/em\u003e has a substantially larger area of occupancy than \u003cem\u003eD. valentini\u003c/em\u003e in southern Georgia (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). \u003cem\u003eD. armeniaca\u003c/em\u003e was recorded in 34 5×5 km squares across southern Georgia, whereas \u003cem\u003eD. valentini\u003c/em\u003e was present in only 14 squares, all of which overlapped with the distribution of \u003cem\u003eD. armeniaca\u003c/em\u003e. Another parthenogen, \u003cem\u003eD. dahli\u003c/em\u003e, also has a broader area of occupancy than its patrilineal ancestor, \u003cem\u003eD. portschinskii\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e\u003ch2\u003eModeling of metapopulation dynamics\u003c/h2\u003e\u003cp\u003eThe simulation model suggested that during the first years of observation the parthenogens are expected to produce larger populations than the sexually breeding lizards. This pattern persisted for approximately the first 10 years of the simulations. Thereafter, the trend changed because extinction occurred more rapidly in the modeled parthenogenetic populations. In the current simulations, more than half of the parthenogenetic populations were lost after roughly 13–15 years, whereas in the sexual breeders this threshold was reached only after about 30–35 years. The median extinction time was 14 years in parthenogens and 34 years in sexual breeders. By year 100, no parthenogenetic populations survived, whereas about 11% of sexual populations were still present; by later time points, both categories had disappeared (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eWe can summarize our data as follows. Parthenogenetic \u003cem\u003eD. armeniaca\u003c/em\u003e, sympatric and syntopic with its patrilineal ancestor, sexually reproducing \u003cem\u003eD. valentini\u003c/em\u003e, tends to: (a) mature earlier (usually after three hibernations, as opposed to 4 hibernations in the sexual breeders); (b) live shorter (rarely survive after four hibernations). Growth deceleration after the third year did not differ significantly between the two species, although a subset of \u003cem\u003eD. valentini\u003c/em\u003e females appeared to maintain relatively high post-maturation growth (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). This pattern coincides with the lower reproductive effort of \u003cem\u003eD. valentini\u003c/em\u003e females from the same population, compared with those of \u003cem\u003eD. armeniaca\u003c/em\u003e (but based on different individuals; Barateli et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). These observed differences are consistent with higher population turnover in D. armeniaca and suggest that it may expand more rapidly across suitable habitats. The simplified model presented here suggests that the parthenogenetic population may grow faster and expand more intensively in neighboring locations than those of the sexual breeder with similar ecology. However, under unstable environmental conditions, the viability of parthenogenetic populations at the local level is lower than that of sexual breeders (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eSuch divergence between closely related, sympatric taxa is not unique to \u003cem\u003eDarevskia\u003c/em\u003e and parallels life-history variation described in other lizard groups. In \u003cem\u003eAgama\u003c/em\u003e, smaller-bodied species display r-like traits and produce larger clutches, whereas larger species invest in fewer, heavier offspring that enhance juvenile survival (Heideman, \u003cspan class=\"CitationRef\"\u003e1994\u003c/span\u003e). In \u003cem\u003eZootoka vivipara\u003c/em\u003e, high-altitude populations are strongly K-selected, with delayed maturity and low mortality, whereas lowland populations mature earlier and reproduce more frequently (Strijbosch \u0026amp; Creemers, \u003cspan class=\"CitationRef\"\u003e1988\u003c/span\u003e). Spinny lizard \u003cem\u003eSceloporus jarrovii\u003c/em\u003e matures earlier and reproduces opportunistically, whereas sympatric \u003cem\u003eSceloporus poinsetti\u003c/em\u003e matures later and reproduces more steadily (Ballinger \u003cspan class=\"CitationRef\"\u003e1973\u003c/span\u003e). These contrasts illustrate how environmental pressures shape life-history divergence and enable the coexistence of related lizard taxa.\u003c/p\u003e\u003cp\u003eIn the studied species of \u003cem\u003eDarevskia\u003c/em\u003e, reproductive mode itself adds another important dimension to these life-history differences. Parthenogens and their sexual relatives diverge in life-history strategy within the same habitat, suggesting that demography and reproductive mode themselves act as major axes of ecological differentiation, given shared spatial and food resources. This demographic contrast is consistent with a colonization–persistence trade-off (Levins and Culver, \u003cspan class=\"CitationRef\"\u003e1971\u003c/span\u003e; Tilman, \u003cspan class=\"CitationRef\"\u003e1994\u003c/span\u003e; Hanski, \u003cspan class=\"CitationRef\"\u003e1999\u003c/span\u003e): parthenogens may colonize suitable habitats more rapidly, whereas sexual species may persist longer under variable conditions.\u003c/p\u003e\u003cp\u003eTo better understand how these demographic patterns relate to coexistence, we place them in the broader context of ecological niche differentiation observed in other lizard assemblages. In numerous studies of lizard community ecology (Pianka, \u003cspan class=\"CitationRef\"\u003e1973\u003c/span\u003e; Schoener, \u003cspan class=\"CitationRef\"\u003e1974\u003c/span\u003e; Losos, \u003cspan class=\"CitationRef\"\u003e1994\u003c/span\u003e; Pianka et al., \u003cspan class=\"CitationRef\"\u003e2017\u003c/span\u003e; Rubalcaba et al., \u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e; Souza-Oliveira et al., \u003cspan class=\"CitationRef\"\u003e2024\u003c/span\u003e), the authors emphasize the niche differences and character displacement of coexisting lizards, assuming that the differences prevent interspecific competition and ensure long-lasting coexistence. In our system, there are indeed some differences in preferred climates and habitats between \u003cem\u003eD. dahli\u003c/em\u003e and \u003cem\u003eD. portschinskii\u003c/em\u003e, both on the macrogeographic (Tarkhnishvili et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e; Petrosyan et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e) and microhabitat (Barateli et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e) scales. Specifically, \u003cem\u003eD. dahli\u003c/em\u003e has a higher altitudinal limit than \u003cem\u003eD. portschinskii\u003c/em\u003e, which is in line with the well-known phenomenon of geographic parthenogenesis (Vrijenhoek and Parker, \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e). When coexisting in the same location, \u003cem\u003eD. portschinskii\u003c/em\u003e is more evenly distributed across the microhabitat and less dependent on proximity to water than \u003cem\u003eD. dahli\u003c/em\u003e (Barateli et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, the overlap in the ranges of these two species is high, and despite negative interactions, they are commonly syntopic (Bakradze, \u003cspan class=\"CitationRef\"\u003e1977\u003c/span\u003e; Tarkhnishvili et al., \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e). Considering this broad overlap of suitable habitats, \u003cem\u003eD. dahli\u003c/em\u003e occupies a larger part of a common suitable range than \u003cem\u003eD. portschinskii\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). There are no remarkable differences in the optimal habitats between \u003cem\u003eD. armeniaca\u003c/em\u003e and \u003cem\u003eD. valentini\u003c/em\u003e; however, the extent of occurrence of \u003cem\u003eD. armeniaca\u003c/em\u003e is broader (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). This pattern of broad habitat overlap, yet wider occupancy by parthenogens, indicates that demographic differences may be more important than niche divergence in shaping this pattern.\u003c/p\u003e\u003cp\u003eWe hypothesize that the broader extent of occurrence and larger area of occupancy of parthenogenetic \u003cem\u003eDarevskia\u003c/em\u003e compared to their paternal ancestors may result primarily from faster reproduction and more effective demographic expansion, rather than from intrinsic differences in ecological niche dimensions. The persistence of these differences through evolutionary time further supports this demographic explanation. The long-term coexistence of parthenogenetic and sexual \u003cem\u003eDarevskia\u003c/em\u003e despite Pleistocene climatic oscillations supports this balance. Yanchukov et al. (\u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e) estimated the age of parthenogenetic \u003cem\u003eDarevskia\u003c/em\u003e at over 0.5 Ma, indicating that neither lineage has replaced the other despite a limited genetic diversity of the parthenogenetic populations. The faster reproduction and expansion of the parthenogens at the metapopulation level appears to be the strategy that ensured their survival over multiple glacial cycles (Freitas et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e; Tarkhnishvili et al., 2025).\u003c/p\u003e\u003cp\u003eSimultaneously, the patrilineal ancestors of the parthenogens may persist longer under unfavorable conditions because of their longer reproductive lifespan. The analysis of reproductive effort, age distribution, and growth dynamics of \u003cem\u003eD. valentini\u003c/em\u003e and \u003cem\u003eD. armeniaca\u003c/em\u003e at Saghamo suggests that sexually breeding females may start reproducing only after the fourth hibernation, and that the reproductive effort of one-quarter of breeding females is low, as evidenced by the left-skewed distribution of RE. Simultaneously, in 20% of females from the same population, growth rates remained almost identical to those of the previous year. This pattern is consistent with the hypothesis that higher reproductive effort may be associated with more rapid growth deceleration and reduced adult persistence.\u003c/p\u003e\u003cp\u003eWhen reproduction fails in one or more consecutive seasons (e.g., due to drought or winter mortality of eggs or hatchlings), sexually breeding species can persist through surviving adults that reproduce in later favorable years. In contrast, parthenogenetic species with their short lifespan and synchronous reproduction after the third hibernation face a higher risk of local extinction under the same conditions. These contrasting demographic strategies may help to explain the stable coexistence of the two reproductive modes across evolutionary timescales. The observed differences in age distribution, modal and highest recorded ages between parthenogens and their sexual ancestors suggest a simple explanation for their long-lasting coexistence. The commonly proposed view that sexual species persist mainly through higher genetic diversity may not fully explain their success. Instead, genetically determined longevity and repeated reproduction likely buffer sexual species during unfavorable periods, whereas parthenogens recover through colonization and rapid growth once conditions improve.\u003c/p\u003e\u003cp\u003eDespite this overall framework, one important question remains open: what mechanisms underlie these demographic contrasts. The answer may relate to the maternal ancestry of \u003cem\u003eD. armeniaca\u003c/em\u003e: \u003cem\u003eD. mixta\u003c/em\u003e, a proven matrilineal ancestor (Murphy, 2000; Tarkhnishvili et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e; Freitas, 2022), shows an age structure more similar to that of the parthenogen than to that of its paternal ancestors. Alternatively, the higher offspring number per individual in the parthenogen, resulting from the absence of males, may enhance population-level success through rapid reproduction. This feature, paralleled by lower individual variation in growth rates and low genetic variation, constrained their adaptive strategy to rapid reproduction rather than a longer lifespan.\u003c/p\u003e\u003cp\u003eTogether, these observations demonstrate that demographic and ecological differentiation is likely to maintain the long-lasting coexistence of ecologically similar parthenogenetic and sexually breeding lizards. Taken together, our findings suggest that \u003cem\u003eDarevskia\u003c/em\u003e provides a rare natural example of long-term coexistence between unisexual and sexual lineages, .associated with contrasting life-history strategies and demographic tendencies that may contribute to long-term coexistence.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eACKNOWLEDGEMENTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe are grateful to Prof. Mzia Zhvania (Institute of Chemical Biology, Ilia State University) and Dr. Nino Pochkidze (Chemical Biology, Ilia State University) for generously providing access to the microtome facilities. We are especially thankful to Dr. Pochkidze, who introduced us to the use of the microtome and supported us with all the necessary materials during the first days of this work. We also thank the bachelor\u0026apos;s degree students (Mariam Mamaladze, Maiam Sabiashvili, David Mamagulashvili, Natali Bordzikuli, Saba Nozadze) \u0026nbsp;who assisted with the skeletochronology preparations, including cleaning the bones and sectioning them with the microtome. Finally, we thank Armen Seropian for his valuable suggestions and constant support throughout this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding.\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003eThis study was conducted with the support of the Shota Rustaveli National Science Foundation under project FR-23-17324.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest.\u0026nbsp;\u003c/strong\u003eNo conflict of interest to declare.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval.\u0026nbsp;\u003c/strong\u003eAll animals were released at the capture site after sampling. No animals were euthanized. The ethics commission of Ilia State University reviewed the methodology and study protocols and approved this research, permit #1018. No permits were required for the field study of the \u003cem\u003eDarevskia\u0026nbsp;\u003c/em\u003especies in Georgia.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate.\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to publication.\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and material.\u0026nbsp;\u003c/strong\u003eAll datasets are included in the supplementary materials for online publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode availability\u003cem\u003e.\u0026nbsp;\u003c/em\u003e\u003c/strong\u003eThe population model included in the supplementary materials in shape of Excel spreadsheet.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions.\u0026nbsp;\u003c/strong\u003eStudy design: NB, DT (equal); field work: NB, GI (equal). Laboratory procedures: NB (leading), GI (supporting); Data analysis: DT, NB (equal); writing: NB, DT (equal).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eArakelyan MS, Danielyan FD (2000) Growth and age composition of some parthenogenetic and bisexual species of Armenian rock lizards (Lacerta). Entomol Rev 80(1):S161\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArakelyan M, Spangenberg V, Petrosyan V, Ryskov A, Kolomiets O, Galoyan E (2023) Evolution of parthenogenetic reproduction in Caucasian rock lizards: a review. 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Biol J Linn Soc 136:293\u0026ndash;305. ttps://doi.org/10.1093/biolinnean/blac023\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"evolutionary-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"evec","sideBox":"Learn more about [Evolutionary Ecology](https://www.springer.com/journal/10682)","snPcode":"10682","submissionUrl":"https://submission.nature.com/new-submission/10682/3","title":"Evolutionary Ecology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"life-history trade-offs, demographic strategy, age structure, parthenogenesis, Darevskia","lastPublishedDoi":"10.21203/rs.3.rs-9127021/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9127021/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eParthenogenetic lineages are often portrayed as rapid colonizers with short lifespans, but how reproductive mode shapes life-history trajectories in close relatives remains unclear. Using Caucasian rock lizards (\u003cem\u003eDarevskia\u003c/em\u003e) as a model, we compared age structure, growth dynamics, and reproductive traits in the hybrid parthenogenetic lizard (\u003cem\u003eD. armeniaca\u003c/em\u003e) and its sexually breeding progenitors (\u003cem\u003eD. valentini\u003c/em\u003e, \u003cem\u003eD. mixta\u003c/em\u003e). Age was inferred by skeletochronology of phalangeal cross-sections; growth was estimated from distances between successive lines of arrested growth (LAGs). Reproductive traits were integrated from published datasets and re-analyzed. Parthenogenetic lineages tended to show age distributions consistent with earlier maturation, higher reproductive allocation, and shorter lifespan than their sexual relatives. \u003cem\u003eD. armeniaca\u003c/em\u003e showed higher reproductive effort relative to body mass, earlier age of maturation, and lower proportion of individuals with long lifespan than its patrilineal progenitor, \u003cem\u003eD. valentini\u003c/em\u003e from the same location. Population modeling suggests that the parthenogens would expand faster throughout neighboring habitats than the sexual breeders, which is in line with the observation that they occupy a greater fraction of suitable habitat within their ranges. These differences suggest a demographic mechanism by which unisexual lineages may expand faster, whereas sexual lineages may persist longer under variable conditions, potentially contributing to their long-term coexistence.\u003c/p\u003e","manuscriptTitle":"Trade-off between local persistence and rapid expansion: a case study of a parthenogenetic lizard species and its sexually reproducing ancestor","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-27 09:33:58","doi":"10.21203/rs.3.rs-9127021/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-05-16T22:13:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-15T13:31:14+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-12T00:22:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"1766479731865049113967828877054534363","date":"2026-03-30T23:04:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"222375530254403523971464264644191370943","date":"2026-03-25T06:24:47+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-25T04:47:23+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-17T13:34:39+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-17T13:33:55+00:00","index":"","fulltext":""},{"type":"submitted","content":"Evolutionary Ecology","date":"2026-03-15T07:47:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"evolutionary-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"evec","sideBox":"Learn more about [Evolutionary Ecology](https://www.springer.com/journal/10682)","snPcode":"10682","submissionUrl":"https://submission.nature.com/new-submission/10682/3","title":"Evolutionary Ecology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ef59d60a-7e17-4e3b-a983-770dece2cb2b","owner":[],"postedDate":"March 27th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-05-16T22:13:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-15T13:31:14+00:00","index":16,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-05-16T22:23:15+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-27 09:33:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9127021","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9127021","identity":"rs-9127021","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}