Ultraviolet signaling in sexually dichromatic Andean lizards

Ultraviolet signaling in sexually dichromatic Andean lizards | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 8 January 2026 V1 Latest version Share on Ultraviolet signaling in sexually dichromatic Andean lizards Authors : Sofía Literas 0000-0003-2206-813X [email protected] , Guillermo Debandi , and Valeria Corbalán Authors Info & Affiliations https://doi.org/10.22541/au.176786295.58709593/v1 211 views 92 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Ultraviolet (UV) reflectance is an important yet understudied component of lizard coloration, and its presence and function remain unexplored in the genus Phymaturus. We analyzed the presence and variation of UV reflectance in two closely related and sexually dichromatic species, Phymaturus palluma and Phymaturus roigorum. Spectral reflectance was quantified from 19 body patches across dorsal, lateral, and ventral regions, and conspicuousness was assessed against the natural rocky substrates where these lizards occur. Colorimetric variables (UV brightness, UV chroma, UV hue) were used to evaluate species and sexual differences using generalized mixed models and multivariate analyses. Both species and sexes exhibited UV reflectance, but its magnitude varied strongly among body patches. Ventral and lateral regions showed consistently higher UV reflectance than dorsal ones, suggesting that UV signals are involved in intraspecific communication, since these regions become visible to conspecifics primarily during social encounters. UV hue was the main driver of species and sex differences across patches, while UV brightness differentiated sexes within species and UV chroma contributed disproportionately to interspecific contrasts. These results reveal a multidimensional UV reflectance pattern in Phymaturus and provide a basis for future studies on the role of UV signals in visual communication. Introduction Coloration has been extensively studied across animal taxa due to its key role in communication and signaling (Hill and McGraw 2006, Names et al. 2019). In recent years, growing attention has been directed toward coloration within the ultraviolet spectrum (UV; 300–400 nm) because of its increasing ecological relevance (Font et al. 2009). Unlike humans, who lack sensitivity to ultraviolet light, many animals possess visual systems capable of detecting UV wavelengths, often through tetrachromatic vision (Cuthill et al. 1999, Kodric–Brown and Johnson 2002). This ability has facilitated the evolution of diverse visual communication mechanisms across multiple animal groups. UV signaling has been documented in birds (Keyser and Hill 1999; Hausmann et al. 2003), fish (Siebeck 2014), insects (Papke et al. 2007), arthropods (Henze and Oakley 2015, Painting et al. 2016), lizards (Macedoni et al. 2002; Whiting et al. 2006), amphibians (Secondi et al. 2012, Tartu et al. 2023), snakes (Crowell et al. 2024), turtles (Steffen et al. 2021), and mammals (Sobral et al . 2022). Among reptiles, and particularly among lizards, several species possess highly acute visual systems with retinal photoreceptors sensitive to UV wavelengths. Examples include species of the genus Gallotia (Molina–Borja and Bohórquez–Alonso, 2023), Platysaurus broadleyi (Fleishman et al. 2011); Simões and Gower 2017), Timon lepidus (Font et al. 2009), Zootoca vivipara (Martin et al. 2015a), Tiliqua rosa (Nagloo et al. 2022), Podarcis muralis (Pérez i Lanuza and Font 2014, Martin et al. 2015a), Ctenophorus decresii (Yewers et al. 2015), and species of the genus Anolis (Pérez i de Lanuza and Font 2014, Osorio 2019). Research on UV reflectance in lizards has shown that signaling often involves specific body regions. For example, UV–reflective areas occur on the throat in Algyroides nigropunctatus (Badiane et al. 2018), Lacerta viridis (Bajer et al. 2010), and Platysaurus broadleyi (Whiting et al. 2006); on gular folds in Anolis lizards (Fleishman and Persons 2001, Macedonia 2001, Stoehr and McGraw 2001); on the mouth corners in Crotaphytus collaris (Lappin et al . 2006); on lateral regions in Podarcis muralis (Ábalos et al. 2016, Names et al. 2019) and Podarcis tiliguerta (Badiane and Font 2021); and on the ventral region in Sceloporus (Robinson et al. 2021, Zúñiga–Vega et al. 2021). In general, UV signals are associated with blue patches visible to the human eye and are more prominent in males (Font and Molina–Borja 2004, Molina–Borja and Bohórquez–Alonso 2023). However, UV reflectance has also been documented in females of species such as Ctenophorus ornatus (LeBas and Marshall 2000), Timon lepidus (Font et al. 2009), Gallotia galloti (Font and Molina–Borja 2004, Molina–Borja et al. 2006), Podarcis erhardii (Marshall and Stevens 2014), and Zootoca vivipara (Martin et al. 2013, Badiane et al. 2020). Most research on UV reflectance has focused on sexual selection (LeBas and Marshall 2000, Bajer et al. 2010, Bohórquez–Alonso and Molina–Borja 2014, Badiane et al. 2020), male territorial competition (Stapley and Whiting 2006, Martin et al. 2015b), fighting ability (Whiting et al. 2006, Martin et al. 2016), and indicators of male quality, including genetic and health status (Martín and López 2009). UV–reflective areas are often located on the ventral region, such as the throat, and on lateral surfaces (e.g., mouth corners, flanks), remaining relatively hidden until displayed in specific postures visible to conspecifics. This is consistent with a signaling function and/or with amplification of other visual signals (Lappin et al. 2006). Thus, UV reflectance in lizards is considered an integral component of intraspecific communication, as patterns are visible to the conspecifics that produce them (Font and Molina–Borja 2004). Nonetheless, the role of UV signals in most species remains incompletely understood (Lisboa et al. 2017). The genus Phymaturus is characterized by marked conservatism across multiple biological traits, despite having undergone extensive evolutionary diversification (Corbalán et al. 2013). All species are saxicolous, viviparous, and herbivorous (Cei 1986), inhabiting Andean and extra–Andean mountain systems in Argentina and Chile. The genus comprises two species groups: the palluma group and the patagonicus group (Cei 1993, Etheridge 1995). The two species studied here, Phymaturus palluma (Molina 1782) and P. roigorum (Lobo and Abdala 2007), both belong to the palluma group. They are phylogenetically and geographically close and exhibit sexual dichromatism (Lobo and Nenda, 2015, Corbalán et al. 2018). Recent studies have focused on the ecology and thermal biology of the genus, highlighting their remarkable thermoregulatory capacity in extreme environments (Corbalán et al. 2013, Vicenzi et al.,2017), physiological adaptations for optimizing energy balance under harsh cold conditions (Vicenzi et al. 2019), and reproductive strategies constrained by climatic limitations (Boretto et al. 2014). However, the role of coloration, particularly in the context of visual communication, remains poorly understood. While interspecific variation in color associated with rocky substrates has been documented in P. roigorum (Corbalán et al. 2013) and melanism patterns in Phymaturus verdugo (Corbalán et al. 2018, Azócar Moreno et al. 2024), significant knowledge gaps persist. To date, ultraviolet reflectance and its potential sexual dimorphism have not been investigated, despite the pronounced sexual dichromatism observed in these species (Corbalán et al. 2018). The aim of this study is to determine whether Phymaturus palluma and P. roigorum exhibit ultraviolet reflectance in any body patch, how conspicuous each patch is relative to the natural background, and whether conspicuousness is associated with sex. This research provides novel insights into the potential role of UV signals, thereby contributing to a better understanding of coloration as a communication mechanism in both male and female lizards. Materials and Methods [1]¿p#1 newcommands Study area The study was conducted in January 2022 and January 2023 in two sampling areas in Mendoza Province, Argentina (Fig. 1). Both surveys were carried out in the same month to minimize potential seasonal variation in UV reflectance during the activity period of individuals. In 2022, P. palluma (Fig. 2) was sampled in Valle de Punta de Vacas, within Aconcagua Provincial Park, Las Heras Department, northwestern Mendoza Province (32° 50’ 43’ ’ S, 69° 45’ 50.80’ ’ W; 2500 m.a.s.l.). This site is characterized by a cold semi-arid climate, with maximum temperatures of 28 °C and minimum temperatures of -4 °C, and a mean annual precipitation of 150 mm (Soria 2003). In 2023, Phymaturus roigorum (Fig. 3) was sampled in La Payunia Provincial Reserve, Malargüe Department, southern Mendoza Province (approximately between 35° 40’–36° 52’ S and 68° 20’–69° 40’ W; 2000–2200 m.a.s.l.). This region has a cold semi-arid climate influenced by the Pacific anticyclone, with precipitation concentrated in winter (Martínez Carretero 2004). It is also characterized by volcanic systems (Llambías 2008) and high levels of species richness and endemism (Corbalán and Debandi 2008). Individual coloration of P. roigorum varies with the type of rock substrate inhabited (Corbalán et al. 2013): individuals from ignimbrites or trachytes display whitish or yellowish tones, whereas those from basaltic rocks tend to be darker. For this study, two types of sites were selected: (1) areas dominated by basaltic rocks and (2) a landscape of yardangs. Yardangs are ignimbrite formations sculpted by wind, oriented unidirectionally, and forming elongated parallel ridges (Corbalán and Debandi 2013). The basaltic sampling sites were Site 1 (36° 20’ 17.9” S, 69° 23’ 31.20” W; 2048 m.a.s.l.) and Site 2 (36° 28’ 8.4” S, 69° 21’ 51.09” W; 2182 m.a.s.l.). The ignimbrite site (Site 3) was located at 36° 29’ 16.8” S, 69° 22’ 14.6” W; 2116 m.a.s.l. Data collection Individuals were captured using a noose. In Valle de Punta de Vacas, we captured 58 adult P. palluma (19 males, 39 females). In La Payunia, we captured 57 adult P. roigorum : 11 males and 16 females on basaltic rocks (9 males and 11 females at Site 1; two males and five females at Site 2), and 14 males and 16 females on ignimbrite rocks (Site 3). After capture, each lizard was placed in an individual cloth bag and transported to the laboratory for reflectance measurements. Body mass was measured with a digital scale (Prec TH 200; precision: 0.1 g, range: 200 g), and snout–vent length (SVL) with a digital caliper (precision: 0.01 mm). All individuals were returned to their exact capture site, previously georeferenced with a GPS (Garmin eTrex Vista HCx), within 48–96 h. [1]¿p#1 newcommands Reflectance measurements in the ultraviolet range Reflectance represents the proportion of incident light reflected by a surface at a given wavelength. Values are expressed as percentages (0–100%), where 0% indicates total absorption and 100% indicates complete reflection (Hecht 2017). This study focused on UV reflectance between 300 and 400 nm. Measurements were obtained with a portable spectrophotometer (Ocean Optics JAZ-EL200). Following Corbalán et al. (2018), lizards were warmed to 32 ± 1 °C, close to the preferred body temperature of both species ( P. palluma : 31.3–38.4 °C, Vicenzi et al. 2017, P. roigorum : 31.3–38.0 °C, Corbalán et al. 2013). This procedure ensured that reflectance was recorded under thermal conditions representative of the animals’ active state. Heating was achieved by placing individuals in containers under one infrared lamp and four incandescent lamps, while body temperature was monitored with an infrared thermometer (Raytek Raynger ST61). Once the target temperature was reached, reflectance spectra were recorded from 19 patches distributed across the dorsal, lateral, and ventral body regions. A bifurcated fiber–optic cable connected to a pulsed xenon light source (PX–2) was positioned at a 45° angle relative to the body surface. The probe tip, covered with a black rubber tube to block ambient light and cut at the same angle, was held five mm from the skin, producing an elliptical measurement area of 10 mm². Reflectance spectra were acquired using OceanView 1.6.5 software (Ocean Optics Inc. 2013), with settings of 10 averaged scans and a Boxcar width of five. Calibration was performed with a diffuse reflectance standard, and white and black references were taken every 20 minutes. The 19 measurements comprised six dorsal patches (head, neck, interscapular region, middle dorsum, posterior region between hind limbs, and tail; Fig. 4a); seven ventral patches (chin, throat, chest, belly-posterior, middle, and lateral- and cloaca; Fig. 4b); and six lateral patches (flank, cheek, shoulder, elbow, mouth corners, and axilla; Fig. 4c). Additionally, because both lizards and their rocky substrates exhibit substantial colour variation, reflectance spectra of rock surfaces were recorded to assess the conspicuousness of UV signals against the natural background. Sampling effort differed between study systems to account for differences in substrate heterogeneity. In Valle de Punta de Vacas, where substrate coloration was more variable, mean UV brightness was calculated from ten independent measurements taken from different rocks. In contrast, in La Payunia, where substrates were more homogeneous, three measurements were taken per rock, with four rocks sampled at Site 1, two at Site 2, and two at Site 3. These differences in sampling design reflect the higher colour heterogeneity in habitats occupied by P. palluma relative to those of P. roigorum . Colorimetric variables Spectral data obtained from the spectrophotometer were analyzed in R v.4.5.2 (R Core Team 2025) using the package pavo v.2.0 (Maia et al. 2019). This package enables the processing of spectral data into biologically meaningful colorimetric variables (Montgomerie 2006). We extracted three variables for each body patch of each individual: UV brightness, UV hue, and UV chroma. We restricted all analyses to the 300–400 nm range to specifically evaluate UV signals, following previous recommendations (Names et al. 2019, Badiane et al. 2020, Badiane and Font 2021, Tartu et al. 2023, Surmacki et al. 2023). UV brightness (B2; 300–400 nm) represents spectral intensity, calculated as the sum of reflectance within the selected spectral range. UV chroma (S1U) quantifies the relative contribution of UV to the total reflectance spectrum, computed as R 300-400 / R 300-700 . UV hue (H1, 300–400 nm) corresponds to the wavelength of maximum reflectance within the UV range. For the calculation of B2 and H1, each spectrum was restricted to 300–400 nm, whereas S1U was computed using the full reflectance spectrum (300–700 nm), as required by its formula. All spectra were smoothed using an interval of 0.2 nm (Maia et al. 2013, 2019). Selection of high UV reflectance patches To identify body patches with high UV reflectance, we calculated the difference between the median UV brightness of each body patch and the mean rock brightness in each habitat. A body patch was classified as high in UV reflectance when this difference exceeded 0.5 standard deviations of the mean rock value. This criterion objectively discriminates body patches whose reflectance consistently exceeds the natural variability of the substrate, minimizing biases related to the limited replication of rock measurements. UV brightness was chosen as the focal colorimetric variable because it quantifies the total amount of light reflected in the UV range and is a widely used metric for assessing signal intensity in studies of animal communication (Whiting et al. 2006, Macedonia et al. 2009, Bajer et al. 2011). Moreover, using the median ensured that at least half of the individuals exhibited reflectance values equal to or greater than that of their environment, making the corresponding patch conspicuous. Statistical analyses To focus on biologically meaningful signals, we retained only those patches that exhibited median brightness values exceeding the mean reflectance of the surrounding rock background in at least one species or sex. Since dorsal patches never exceeded the UV reflectance threshold relative to the rock background, only lateral and ventral patches were included in subsequent analyses. Multivariate differences in UV reflectance were assessed using PERMANOVA, testing the effects of species, sex, and their interaction across the three standardized variables (z–score). Patches were aggregated into two body regions: lateral (flank, cheek, shoulder, elbow, mouth corners, and axilla) and ventral (chin, throat, chest, and belly). This approach allowed us to evaluate whether UV reflectance signals are organized at the level of broader anatomical regions rather than isolated patches, which is biologically relevant given that lizards typically expose entire flanks or ventral surfaces during social interactions. To visualize the multivariate separation, we conducted a canonical analysis of principal coordinates (CAP) constrained by species and sex and verified homogeneity of dispersion with PERMDISP. PERMANOVA was implemented with the function ‘ adonis2’ from the ‘ vegan’ package (Oksanen et al. 2022), using Bray–Curtis distances, 9999 permutations, and restricting permutation within sampling sites (Anderson 2005). To identify which spectral variables (UV brightness, UV chroma or UV hue) contributed most to between-group dissimilarities, we performed a contribution to dissimilarity analysis adapted from SIMPER using Euclidean distance. Arbitrarily, a single variable was retained when its individual contribution exceeded 60% of the total dissimilarity or when it surpassed that of the second variable by more than 15%. Two variables were retained when the difference between their contributions was less than 10% and both contributed at least 30%. These criteria reduced redundancy and guided the selection of variables for univariate modelling (Anderson et al. 2008). Generalized linear models (GLM) or generalized linear mixed models (GLMMs) were fitted using the ‘ glmmTMB’ package (Brooks et al. 2017), depending on the data structure, testing species, sex, and their interaction for each retained variable and body patch. GLMMs were applied when including individuals as a random effect improved model fit. Model diagnostics were conducted with the ‘ DHARMa’ package (Hartig 2022). For UV hue, models often showed poor residual fit, therefore, a robustness analysis by parametric bootstrapping (2000 iterations) was performed to obtain empirical confidence intervals and assess the stability of fixed effects without relying on normality assumptions. Bootstrap p–values were calculated as the proportion or replicates in which the null hypothesis was not rejected (two–tailed). To account for multiple comparisons across models, we applied the Benjamini–Hochberg (B–H) procedure to control the false discovery rate (FDR). Corrections were implemented at the level of hypothesis families (species, sex, and their interaction within each patch and spectral variable) balancing type I and type II errors. For each model, we report adjusted p -values, coefficients, 95% confidence intervals, and marginal and conditional R² values (‘ MuMIn’ package, Bartoń 2025). All analyses were conducted in R v4.5.2 (R Development Core Team 2025). Results Both species, in both sexes, exhibit reflectance within the ultraviolet range. Out of the 19 body patches evaluated, six ventral and three lateral patches show UV reflectance higher than that of the surrounding rocks in both species. The posterior belly, cloaca, and axilla are the patches with the highest UV brightness values. None of the dorsal patches exceed the defined threshold, as UV brightness values are consistently lower than those of the rocky substrates (Supporting Information, Fig. S1). The selected patches are used for subsequent analyses. Canonical analysis of principal coordinates (CAP) reveals differences in UV reflectance between species and sexes (Fig. 5). In the lateral region, sexual differentiation is more pronounced in P. palluma , whereas P. roigorum shows greater overlap between males and females. In contrast, ventral patches exhibit a clear separation between sexes in both species. These patterns are consistent with PERMANOVA results, which indicate that UV variables differ significantly according to species, sex, and their interaction (Table 1). Specifically, in ventral patches, the species–sex interaction is significant (F = 7.16; p = 0.001), as well as in lateral patches (F = 8.96; p = 0.002). However, effect sizes for these factors are relatively small. PERMDISP analyses further reveal significant differences in multivariate dispersion among groups, both in ventral (F = 23.73; p = 0.001) and lateral regions (F = 12.95; p = 0.001; Table 1). This result indicates that part of the observed variance is associated with heterogeneity in dispersion, such that separation in CAP space reflects both centroid shifts and differences in group spread. Contribution to dissimilarity analyses (SIMPER) shows that the relative importance of each UV variable (brightness, chroma, hue) to interspecific and sexual differences varies notably (Table 2). UV brightness predominates in the middle belly and axilla (65–85%), being important in comparisons involving females of both species in those patches and also in posterior belly and cloaca. UV hue accounts for intraspecific sexual differentiation in the lateral belly, posterior belly, and cloaca (62–84%) for both species, and in chin and throat for P. roigorum . UV chroma is most relevant in interspecific comparisons between males in the lateral belly and elbow (62–89%). In gular patches (chin and throat) and the mouth corners, contributions of the three variables are more balanced, with no single dominant descriptor, suggesting more complex reflectance patterns. Significant effects of species, sex, and their interaction on UV reflectance are detected across several body regions (Fig. 6, Table 3). Overall, species differences are more frequent in the ventral regions (particularly the lateral, middle, and posterior belly, and cloacal patches), whereas sexual dimorphism appears mainly in chin, throat, axilla, and mouth corners patches (Fig. 6). Significant species–sex interactions are detected in multiple regions, suggesting that the degree of sexual differentiation varies between species. In the chin, throat, and mouth corners, males show higher UV chroma than females, being more marked for P. palluma than for P. roigorum . In the middle belly and axilla, P. palluma females display significantly higher UV brightness than conspecific males, while a similar pattern is shown for hue in the mouth corners and the cloaca (Fig. 7). In most cases where significant interactions occur, P. roigorum shows lower values than P. palluma . In patches without significant interactions, species and sex effects are consistent. In the posterior belly and cloaca, P. palluma shows higher UV brightness and hue than P. roigorum , whereas P. roigorum exhibits higher UV chroma. Regardless of the species, females of both species display higher UV brightness and UV hue than males. Similarly, for the lateral belly, P. roigorum exhibits higher UV chroma, whereas P. palluma shows higher UV hue. In the elbow, P. roigorum has higher UV chroma, and P. palluma has higher UV hue, with a significant interaction for brightness indicating a more complex pattern for that variable (Table 3; full model results are provided in Supporting Information Table S1). Discussion Ultraviolet (UV) reflectance is a key component of visual communication in lizards, mediating social and reproductive interactions. This study provides the first characterization of UV reflectance patterns in two closely related and sexually dichromatic lizards of the genus Phymaturus : the Andean P. palluma and the extra Andean P. roigorum . We found sexually dimorphic UV patterns concentrated on ventral and lateral body regions, with negligible UV reflectance on the dorsum. This distribution supports the commonly proposed evolutionary trade-off between dorsal crypsis against predators and ventral signaling to conspecifics (Marshall and Stevens 2014). Interestingly, patches with high UV reflectance are not associated with visible blue color, as reported for other species (LeBas and Marshall 2000, Abramjan et al. 2020). In fact, some patches, such as the chin and throat, appear generally dark to the human eye. In contrast to the general pattern described for lizards, UV reflectance in Phymaturus was female–biased, with females of both species displaying higher UV brightness and UV hue than males across many ventral and lateral body patches. Beyond confirming this general pattern, our analyses reveal a complex scenario where the contribution of different colorimetric UV variables (hue, brightness, and chroma) varies markedly among body patches, sexes, and species. Although UV vision has not been specifically studied in Phymaturus , its presence in other diurnal lizards (Pérez i de Lanuza and Font 2014) and the phylogenetic conservation of visual systems (Fleishman et al. 2011, Fleishman 2024) make it plausible that these signals are perceptible to conspecifics. The ventral (chin, throat, chest, belly, cloaca) and lateral (mouth corners, axilla) patches exhibiting high UV reflectance are known signal hubs in lizards. In a particular light environment, a colour pattern is most conspicuous if its adjacent colour pattern elements vary greatly in brightness or chroma (Endler 1992). Thus, some patches such as axilla or elbow (or even mouth corners), involved in sexual recognition according to our results, could be particularly advantageous for detectability in the dark crevices that these lizards use as refuges. Ventral UV patches, instead, can only be seen by their conspecifics if the lizards develop some display that leaves these parts exposed. In such cases, UV–reflective patches may work together with specific behavioural displays to increase the visibility of the signal during close–range interactions, as described for the ventrolateral UV–blue patches in Podarcis muralis (Pérez i de Lanuza and Font 2015) and the UV–reflective mouth corners patches in Crotaphytus collaris (Lappin et al. 2006). Several displays were recorded in Phymaturus species, such as head–bobbing behaviour (which consist in the up–and–down movement of the head or anterior part of the trunk in both sexes, Vicenzi and Vicente 2023). The first unit of the P. palluma headbob display may function as a determinant for sex recognition, but the amplitude and duration of subsequent units provide different types of information (species identity, sex, and social context) to the receiver (Vicenzi and Vicente 2023). Similar behaviours have been interpreted as multicomponent signals in other iguanian lizards, combining head movements and the exposure of coloured areas during close-range interactions (Vicente 2018). Head–bobbing leaves exposed chin, throat and axillas, patches whose UV reflectance may function as a conspicuous signal by generating strong contrast against the background, as reported for Ctenophorus ornatus (LeBas and Marshall 2000). In male–male interactions of P. palluma (when territorial intrusion of another rival male occurs), individuals display simultaneously other behaviors such as gular expansion, lateral compression, and back arching of the trunk (Vicenzi and Vicente 2023). Therefore, in these occasions not only chin and throat but also chest, belly and cloaca are exposed. In P. palluma these displays could represent honest indicators of the fighting abilities, or dominance (Vicenzi and Vicente 2023), and as occurs with alone head–bobbing display, they could be seen by congeners from different points across the rocky promontory where they inhabit. In other liolaemids, another behaviour where the axilla is exposed is the fore limb wave display, which consists in raising a single foreleg one or more times while the lizard remains standing upright on two front legs or on all four (Halloy and Castillo 2006). Although this behaviour (which may signal an assertive and/or challenging lizard), was not described for Phymaturu s species, it is plausible to occur. The mouth corner requires a deeper attention since it could be involved directly in signalling dominance status. Lappin et al. (2006) found that a gaping display in adult male of collared lizards, contains information about fighting ability, as it exposes the adductor muscle complex, a reliable and visually enhanced morphological cue of weapon performance. This behaviour (which was also observed in P. palluma ; Corbalán, pers. obs.), may resolve conflicts, reducing the risk of injury that goes with engaging in a fight. UV patches around mouth corners may act as amplifiers, as they enhance the visibility of the adductor muscle complex during frontal gaping displays (Lappin et al. 2006). Considering that UV patches in mouth corners are more conspicuous in males, especially in P. palluma , further studies in this way could help to understand the role of these patches in Phymaturus species. A colorimetric dissection of these patterns showed that UV hue was the primary driver of dissimilarity between sexes and species across most body patches. For instance, P. palluma consistently exhibited higher UV hue than P. roigorum , and females showed higher UV hue values than males. This suggests that hue may be the most informative component for conveying identity (species or sex) within the Phymaturus visual system, consistent with its role in other lizards like Podarcis muralis (Badiane and Font 2021). UV brightness differentiated sexes within species, particularly in regions such as the middle belly and axilla, where we found significant species–by–sex interactions (e.g., P. palluma females are brighter than conspecific males). UV chroma was most relevant for interspecific divergence, being consistently higher in P. roigorum . A critical finding was the presence of significant species by sex interactions, showing that sexual dimorphism is not evolutionarily conserved between these closely related taxa. The reversal in chroma patterns between P. palluma and P. roigorum on the chin, throat, and mouth corners suggests divergent evolution of sexual signals, potentially driven by selective pressures related to their different habitat backgrounds. Furthermore, females of both species displayed systematically higher UV brightness and hue than males in key ventral patches. This pattern, observed in other vertebrates like Rhinella spinulosa (Tartu et al. 2023) and in female lizards like Tropidurus spinulosus (Rossi et al. 2019) , Ctenophorus ornatus (LeBas and Marshall 2000), Crotaphytus dickersonae (Macedonia et al. 2009), suggests that UV brightness could function as a female specific signal in Phymaturus , potentially indicating reproductive state. While female coloration is sometimes linked to unreceptiveness (e.g., Zootoca vivipara , Martin et al. 2013), it can also attract mates (e.g., Ctenophorus ornatus , LeBas and Marshall 2000). Given that our sampling period coincides with vitellogenesis in Phymaturus species (Boretto et al. 2007, 2014), the elevated UV in females could be associated with reproductive state. The higher female brightness in P. palluma than P. roigorum suggests additional modulation by species–specific physiological or environmental factors. Finally, the low UV reflectance on the dorsum and its concentration in less exposed ventral and lateral regions supports the hypothesis of an adaptive trade–off between crypsis and communication (Marshall and Stevens 2014). This spatial organization suggests that UV signals may serve social or reproductive functions without significantly increasing vulnerability to aerial predators capable of detecting UV wavelengths. Taken together, our results show that UV reflectance in Phymaturus is sexually dimorphic, exhibits species-specific patterns in certain body regions, and is concentrated in areas that are functionally relevant for social interaction. 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Figure 4 Body patches of the lizards where reflectance was measured. (a) Dorsal patches: head, nape, interscapular region, middle dorsum, posterior region, and tail. (b) Ventral patches: chin, throat, chest, belly (posterior, middle and lateral) and cloaca. (c) Lateral patches: mouth corners, cheek, shoulder, elbow, axilla and flank. Figure 5 Canonical Analysis of Principal Coordinates (CAP) showing UV–colorimetric variation across ventral and lateral body regions. Centroids represent group means for species and sexes. Ellipses indicate 95% confidence intervals. [1]¿p#1 newcommands Figure 6 Significance of species, sex, and interaction effects on UV reflectance across body patches. Figure 7 Variable Interaction Effects of Species and Sex across body patches. [1]¿p#1 newcommands Tables Table 1 Multivariate analysis of variance (PERMANOVA) and dispersion (PERMDISP) results for UV–colorimetric differentiation between Phymaturus species and sexes. Body Region Analysis Factor DF F R² p Ventral PERMANOVA Species 1 33.15 0.089 < 0.001 Sex 1 98.47 0.117 < 0.001 Species × Sex 1 7.16 0.086 < 0.001 PERMDISP Groups 3 23.73 - < 0.001 Lateral PERMANOVA Species 1 21.83 0.056 < 0.001 Sex 1 22.22 0.057 < 0.001 Species × Sex 1 8.96 0.023 0.002 PERMDISP Groups 3 12.95 - < 0.001 [1]¿p#1 newcommands Table 2 UV variables driving group differences are retained for generalized linear mixed models (GLMMs) after SIMPER analysis. Pp = P. palluma ; Pr = P. roigorum ; ♂ = male; ♀ = female. Middle belly Pp♀ – Pr♀ UV brightness 65.49 – – Pp♂ – Pr♂ UV hue 48.85 UV brightness 45.04 Pp♀ – Pp♂ UV brightness 66.37 – – Pr♀– Pr♂ UV hue 72.58 – – Lateral belly Pp♀ – Pr♀ UV chroma 48.98 – – Pp♂ – Pr♂ UV chroma 88.99 – – Pp♀ – Pp♂ UV hue 84.11 – – Pr♀– Pr♂ UV hue 61.45 – – Posterior belly Pp♀ – Pr♀ UV brightness 51.78 – – Pp♂ – Pr♂ UV chroma 54.38 – – Pp♀ – Pp♂ UV hue 53.07 – – Pr♀– Pr♂ UV hue 78.12 – – Chin Pp♀ - Pr♀ UV hue 78.08 – – Pp♂ - Pr♂ UV chroma 46.06 UV hue 39.92 Pp♀ - Pp♂ UV chroma 44.85 UV hue 35.47 Pr♀- Pr♂ UV hue 39.26 UV chroma 36.97 Throat Pp♀ - Pr♀ UV hue 47.59 UV brightness 43.07 Pp♂ – Pr♂ UV chroma 35.22 UV hue 34.61 Pp♀ – Pp♂ UV chroma 36.21 UV brightness 34.45 Pr♀– Pr♂ UV hue 40.07 UV chroma 38.63 Cloaca Pp♀ – Pr♀ UV brightness 40.88 – – Pp♂ – Pr♂ UV chroma 40.74 UV hue 31.94 Pp♀ – Pp♂ UV hue 57.04 – – Pr♀– Pr♂ UV hue 71.79 – – Elbow Pp♀ – Pr♀ UV chroma 52.66 – – Pp♂ – Pr♂ UV chroma 61.52 – – Pp♀ – Pp♂ UV brightness 76.16 – – Pr♀– Pr♂ UV hue 70.93 – – Mouth cornes Pp♀ – Pr♀ UV chroma 44.18 UV hue 35.73 Pp♂ – Pr♂ UV chroma 45.12 UV hue 41.85 Pp♀ – Pp♂ UV chroma 44.93 UV hue 39.84 Pr♀– Pr♂ UV chroma 45.49 UV hue 40.17 Axilla Pp♀ – Pr♀ UV brightness 84.73 – – Pp♂ – Pr♂ UV brightness 62.04 – – Pp♀ – Pp♂ UV brightness 77.47 – – Pr♀– Pr♂ UV hue 63.81 – – Table 3 Summary of GLMM results for the effects of species, sex, and their interaction on UV reflectance (UV brightness, UV chroma, and UV hue) across body patches. Full statistical outputs, including bootstrap–derived p –values for UV hue, are available in Supporting information, Table S1. Chin UV chroma species ( P. roigorum ) -0.041 0.15 -0.273 0.783 sex (male) 1.783 0.177 10.075 <0.001*** species × sex -0.958 0.243 -3.942 <0.001*** UV hue species ( P. roigorum ) 0.332 – – 0.139 sex (male) -1.41 – – <0.001*** species × sex 0.535 – – 0.065 Throat UV brightness species ( P. roigorum ) -0.338 0.168 -2.012 0.045* sex (male) -1.477 0.202 -7.312 <0.001*** species × sex 0.961 0.271 3.546 <0.001*** UV chroma species ( P. roigorum ) -0.083 0.143 -0.58 0.563 sex (male) 1.541 0.168 9.173 <0.001*** species × sex -0.643 0.231 -2.784 0.005 UV hue species ( P. roigorum ) 0.39 – – 0.100 sex (male) -1.249 – – <0.001*** species × sex 0.324 – – 0.233 Middle belly UV brightness species ( P. roigorum ) -0.795 0.136 -5.846 <0.001*** sex (male) -0.711 0.155 -4.587 <0.001*** species × sex 0.754 0.226 3.336 <0.001*** UV chroma species ( P. roigorum ) 0.249 0.154 1.617 0.105 sex (male) -0.098 0.184 -0.533 0.587 species × sex 0.393 0.249 1.578 0.115 UV hue species ( P. roigorum ) -0.159 – – 0.088 sex (male) -0.248 – – 0.196 species × sex -0.538 – – 0.062 Lateral belly UV chroma species ( P. roigorum ) 0.654 0.162 4.037 <0.001*** sex (male) 0.128 0.189 0.677 0.495 species × sex 0.483 0.261 1.851 0.063 UV hue species ( P. roigorum ) -0.33 – – 0.002** sex (male) -1.725 – – <0.001*** species x sex 0.465 – – 0.067 Posterior belly UV brightness species ( P. roigorum ) -0.709 0.132 -5.371 <0.001*** sex (male) -0.476 0.141 -3.376 <0.001*** species × sex 0.524 0.28 1.871 0.060 UV chroma species ( P. roigorum ) 0.381 0.143 2.664 0.008** sex (male) -0.302 0.176 -1.716 0.087 species × sex 0.377 0.252 1.496 0.134 UV hue species ( P. roigorum ) -0.438 – – 0.004** sex (male) -1.172 – – <0.001*** species × sex 0.156 – – 0.618 Mouth corners UV chroma species ( P. roigorum ) 0.664 0.153 4.34 <0.001*** sex (male) 2.522 0.188 13.415 <0.001*** species × sex -2.041 0.254 -8.035 <0.001*** UV hue species ( P. roigorum ) -0.55 – – 0.008** sex (male) -2.214 – – <0.001*** species × sex 1.794 – – 0.001** Axilla UV brightness species ( P. roigorum ) -1.355 0.203 -6.675 <0.001*** sex (male) -1.062 0.238 -4.462 <0.001*** species × sex 0.995 0.329 3.024 0.002** UV hue species ( P. roigorum ) -0.142 – – 0.331 sex (male) -0.289 – – 0.142 species × sex -0.041 – – 0.89 Elbow UV brightness species ( P. roigorum ) -0.588 0.128 -4.594 <0.001*** sex (male) -0.442 0.155 -2.852 0.004** species × sex 0.48 0.21 2.286 0.022* UV chroma species ( P. roigorum ) 1.431 0.179 7.994 <0.001*** sex (male) -0.078 0.222 -0.351 0.724 species × sex 0.134 0.294 0.456 0.649 UV hue species ( P. roigorum ) -0.699 – – 0.001** sex (male) -0.068 – – 0.733 species × sex -0.169 – – 0.617 Cloaca UV brightness species ( P. roigorum ) -0.787 0.196 -4.015 <0.001*** sex (male) -0.357 0.292 -1.222 0.228 species × sex 0.172 0.332 0.518 0.604 UV chroma species ( P. roigorum ) 0.554 0.184 3.011 0.003** sex (male) -0.224 0.244 -0.918 0.357 species × sex 0.451 0.323 1.396 0.162 UV hue species ( P. roigorum ) -0.611 – – 0.008** sex (male) -0.633 – – <0.001*** species × sex -0.235 – – 0.001** Statistical significance is indicated as: * p < 0.05; ** p < 0.01; *** p < 0.001. Information & Authors Information Version history V1 Version 1 08 January 2026 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords body patches chromatic signaling phymaturus sexual dimorphism spectral reflectance ultraviolet reflectance Authors Affiliations Sofía Literas 0000-0003-2206-813X [email protected] CONICET Mendoza View all articles by this author Guillermo Debandi INTA View all articles by this author Valeria Corbalán Instituto Argentino de Investigaciones de las Zonas Áridas (IADIZA-CONICET) View all articles by this author Metrics & Citations Metrics Article Usage 211 views 92 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Sofía Literas, Guillermo Debandi, Valeria Corbalán. Ultraviolet signaling in sexually dichromatic Andean lizards. Authorea . 08 January 2026. 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