Thermoregulation in two syntopic Galápagos land iguanas: the role of microhabitat selection and skin pigmentation

Thermoregulation in two syntopic Galápagos land iguanas: the role of microhabitat selection and skin pigmentation | 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 Thermoregulation in two syntopic Galápagos land iguanas: the role of microhabitat selection and skin pigmentation Lorenzo Garizio, Marco Gargano, Paolo Gratton, Silvio Marta, Giuliano Colosimo, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8116905/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Thermoregulation in reptiles depends on the interplay between environmental conditions, genetic adaptation and phenotypic plasticity. Behavioral strategies and skin pigmentation are among the main factors influencing the ability of reptiles to modulate heat transfer with the environment. The critically endangered Galápagos pink land iguana ( Conolophus marthae ) displays a unique coloration, due to the absence of pigments across large portions of its body. In this study, we compared thermoregulatory strategies of C. marthae and the syntopic population of yellow iguana ( C. subcristatus ) on Wolf Volcano (Isabela Island, Galápagos). While the two species display similar body temperatures, C. marthae tends to expose itself to lower levels of ultraviolet B (UVB) irradiance. This difference reflects contrasting microhabitat use, with pink iguanas occupying shaded areas more frequently than yellow iguanas. The lack of photoprotective pigments in the pink iguana’s dermis may explain this behavior, as prolonged exposure to UV irradiance can be detrimental to iguana health. The avoidance of high solar radiation highlights the role of microhabitat features in meeting the thermoregulatory requirements of the pink iguana, which may preferentially select areas with denser vegetation that provides shelters and shade. Thus, the distinctive partial skin depigmentation of the pink iguana, which is otherwise interpretable as detrimental, may instead shape microhabitat selection, reduce competition, and ultimately facilitate coexistence with C. subcristatus . thermal ecology reptiles GAM UV radiation habitat use Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Thermoregulation, i.e. , the modulation of body temperature in response to environmental conditions, is a fundamental homeostatic biological process (Wieser, 1973 ; Huey, 1982 ; Angilletta et al., 2004). Ectothermic organisms cannot generate enough metabolic heat to maintain a body temperature significantly different from the surrounding environment. To thermoregulate, they have evolved a diverse range of behavioral and physiological adaptations (Hutchison & Maness, 1979 ; Stevenson, 1985 ; Seebacher, 2009 ). Non-avian reptiles (hereafter “reptiles”) possess a remarkable adaptability, enabling them to occupy a wide variety of habitats across the tropical and temperate regions (Roll et al., 2017 ). Among the behavioral adaptations reptiles employ to regulate their body temperature, basking involves warming up by exposing the body to sun rays or warm surfaces, an activity that may take up a large fraction of their daily time budget (Gvoždík, 2002 ). Basking reptiles adopt different strategies to modulate heat exchange; these include adjusting their position, posture, duration of exposure to sun rays, and selecting the appropriate basking surface (Seebacher, 1999 ). Thermoregulatory behaviors additionally involve cooling strategies, such as avoidance of direct sunlight, selection of colder microhabitats and use of shelters (Aguilar & Cruz 2010 ; Grimm-Seyfarth et al., 2017 ). Frequency and duration of basking are influenced by the physiological and structural constraints of each species ( e.g. , the body size) as well as the thermal conditions of their environment (Giacometti et al., 2023 ). Non-behavioral traits also influence thermoregulation. For instance, skin coloration affects the efficacy of heat absorption from sun radiation. Indeed, dark-colored surfaces have lower reflectance than light-colored ones. Consequently, dark bodies absorb more solar radiation than lighter-colored bodies, resulting in higher heating rates. Therefore, skin pigmentation significantly influences thermoregulatory efficiency of ectotherms (Stuart-Fox et al., 2017 ). In reptiles, differences in both heating rates and body temperature were observed between wildtypes and melanic morphs (Azócar et al., 2020 ; Clusella-Trullas et al., 2009 ). Skin pigmentation also plays a role in responses to stress deriving from exposure to ultraviolet (UV) radiation (McNamara et al., 2021 ), and melanin-based coloration seems to be associated with photoprotective functions (Kumaş et al., 2017 ). Excessive exposure to UV radiation may lead to reptiles’ skin and eye damage as well as diminished reproductive success (Ferguson et al., 2002 ; Gardiner et al., 2009 ). Nevertheless, exposure to sunlight is necessary for other physiological processes, such as the biosynthesis of vitamin D (Ferguson et al. 2002 ), which plays a crucial role in regulating calcium absorption, cell signaling and immune responses (Lips, 2006 ; Boyan et al., 2002 ; Bishop et al., 2021 ). The thermal properties of the environment are among the main factors affecting the distribution of reptiles (Guisan & Hofer 2003 ; McCain, 2010 ). Indeed, thermoregulation requirements shape the habitat selection in reptiles, both at the macro- and microscale level ( e.g. , Row & Blouin-Demers, 2006 ; Harvey & Weatherhead, 2010 ; Gifford et al., 2012 ). Complex environments with both sunny and shaded spots represent suitable habitats for many species, as they provide opportunities to regulate the exposure to solar radiation efficiently. For this reason, reptiles’ occurrence is frequently associated with ecotones between open and vegetated areas (Madani et al., 2024 ). Because microhabitat selection is related to thermoregulation requirements, the habitat usage by reptiles is influenced by both seasonality (Ortega & Pérez-Mellado, 2016 ) and regional differences (Price-Rees et al., 2013 ). Seasonal variations predominantly affect reptiles’ microhabitat selection in temperate areas, where they usually select sun-exposed microhabitats, especially during colder periods, to warm up and reach suitable body temperatures ( e.g ., Langkilde et al., 2003 ). By contrast, in tropical lowlands, where temperatures are higher throughout the year, reptiles can more easily maintain elevated body temperatures through thermoregulation. Consequently, habitat selection is more likely to be driven by the need to avoid overheating than by finding basking sites (Price-Rees et al., 2013 ). The Galápagos pink land iguana ( Conolophus marthae Gentile & Snell, 2009 ; hereafter “pink iguana”) is one of the most iconic terrestrial animals of the Galápagos archipelago, and a flagship species for conservation (Gentile & Snell, 2009 ; Gentile et al., 2016 ). The only known population of pink iguanas occurs in tropical dry shrublands and tropical dry forests on the top and northern slopes of Wolf Volcano on Isabela Island (Fig. 1 ). The adult population size of the pink iguana amounts to only ca. 200 individuals (Garizio et al., 2024 ) occupying an extremely limited range ( ca. 42 Km 2 ; Gargano et al., submitted. ). For this reason, the species has been classified as “critically endangered” in the IUCN Red List (Gentile, 2012 ). Since its description, the peculiar coloration of C. marthae has prompted questions on its evolutionary and ecological significance. The head and a large portion of the body of the species appear pink, as well as the anterior legs; the middle-posterior part of the body typically presents a black-striped pattern, whereas the tail and the posterior legs are black (Figure S1 ; Gentile & Snell, 2009 ). The extension of pink and black portions can vary between individuals. This color pattern is unique within the Iguanidae, including those inhabiting the Galápagos archipelago. Marine iguanas ( Amblyrhynchus cristatus ) generally display a dark coloration, whereas Galápagos land iguanas ( C. subcristatus , hereafter “yellow iguana”) and Barrington land iguanas ( C. pallidus ) both exhibit yellowish-brownish colorations (Figure S1 ). Histological analysis of skin samples showed that the pink areas of C. marthae are associated with a complete lack of pigmentary cells, whereas melanocytes occur in the skin of C. subcristatus and are particularly abundant in A. cristatus (Lewbart et al., 2023 , Scimeca et al., 2025 ). Moreover, the stratum laxum of the pink iguana’s dermis displays a complex network of large capillaries, absent in the other Galápagos iguana species (Lewbart et al., 2023 ). Ultimately, the pink color of pink iguanas is not due to a pigment, but in fact caused by blood flowing through abundant, connected vascular channels in the stratum laxum, which lacks protective melanophores. Previous research (Gustavino et al., 2014 ) reported elevated nuclear DNA (nDNA) damage in the erythrocytes of pink iguanas, likely due to high exposure to UVB radiation, along with lower vitamin D levels compared to other Galápagos species (Di Giacomo et al., 2022 ). Since skin pigmentation plays a key role in both photoprotection (McNamara et al., 2021 ) and thermoregulation (Stuart-Fox et al., 2017 ), differences in coloration may drive species-specific basking behaviors and thermal strategies. The lack of photoprotective pigments in its skin may impact C. marthae ’s tolerance to intense solar radiation, promoting behavioral avoidance of peak sun exposure. As a result, C. marthae could experience reduced thermoregulatory efficiency and suboptimal body temperatures compared to the syntopic population of C. subcristatus on Wolf Volcano. Alternatively, the two species may adopt different thermoregulatory strategies, relying on different daily activity patterns, microhabitat preferences, or behavioral adjustments that reflect divergent responses to the same environmental conditions. From this perspective, the syntopic occurrence of C. marthae and C. subcristatus on Wolf Volcano offers a unique opportunity to test these hypotheses by comparing their thermal ecology and habitat use. Specifically, we hypothesize that the partial lack of photoprotective pigments in C. marthae ’s skin leads to behavioral avoidance of intense solar radiation, resulting in a thermoregulatory niche that differs from that of C. subcristatus . To evaluate this, we first analyzed data collected during monitoring activities to test for interspecific differences in thermoregulatory niche, defined as the bivariate space composed of body temperature and UVB exposure, by fitting Generalized Additive Models (GAMs). Furthermore, we hypothesized that differences in microhabitat use contribute to these patterns, with C. marthae expected to occur more frequently in areas offering opportunities for shading. To test this, we modelled species occurrence associated with the presence of natural shelters linked to thermoregulation. We investigated the use of microhabitat features linked to thermoregulation by fitting a binomial GAM to determine whether C. marthae and C. subcristatus occurrence differs in relation to the presence of natural shelters that provide opportunities for shading. 2. Materials and methods 2.1 Sampling activities During two field campaigns conducted on the north-western slopes of Wolf Volcano in 2014 (15–23 June) and 2016 (31 August – 4 September), 69 C. marthae (42 males and 27 females) and 59 C. subcristatus (35 males and 24 females) individuals were captured. All data used for our analysis involve iguanas sighted in the northwestern portion of the Wolf Volcano rim, within an area of ca. 2 km 2 and ranging from about 1500 to 1650 m asl (Fig. 1 , inset). Mature pink and yellow iguanas congregate in this location for mating during the wet season, from January/February through August/September (Trueman & D'Ozouville, 2010 ; Gentile et al., 2016 ; Onorati et al., 2016 ; Gargano et al., 2024 ), whereas recent evidence indicates that C. marthae probably moves to lower areas during the dry season (Colosimo et al., 2022 ). GPS coordinates, hour of capture ( time ), species ( species ), sex ( sex ), snout-vent-length ( SVL , in cm), and body mass ( mass , in kg) were recorded for each captured iguana. Given the difficult logistics of the area, we could not adopt focal animal sampling to record the time spent on thermoregulatory behaviors such as basking and sheltering. Nevertheless, a standardized protocol to obtain information on environmental conditions related to temperature and solar radiation at capture events (i.e., exact location and time of day) was applied. Through the employment of a Solarmeter® Model 6.2 Sensitive UVB Meter, we recorded the intensity of UVB irradiance at sighting position ( UVB ). UVB was recorded by placing the sensor perpendicular to the iguana’s longitudinal axis (head–tail) orienting it to create a 45-degree angle with the ground, selecting the body side most prominently exposed to sunlight. This positioning aligned the sensor surface with the direction of the incident solar radiation. For most of the sightings (n = 111, out of 128), we also measured the maximum UVB irradiance ( UVB max ) in the environment by pointing the UVB meter directly towards the sun. We measured the surface body temperature ( bodyT ) of iguanas by means of an I-R Thermometer, and the air temperature in the shade ( airT ) with an air thermometer. Finally, we collected data on the iguanas’ position in relation to shelters, such as bushes and trees, in order to represent their microhabitat utilization in response to solar radiation. Such information was summarized in the categorical variable microhabitat , considering a 3-m radius buffer around the capture location of each iguana, where vegetation cover was assessed. This variable includes three levels: “shade”, when iguanas were sighted in completely shaded sites, ( i.e. , areas entirely covered by bushes and/or trees); “partial shade”, when sites had partial canopy cover; and “sun”, when iguanas were observed in open areas (lacking tree or shrub cover). Handling of animals was performed in accordance with the protocol approved by the Galápagos National Park Directorate (GNPD), the governmental authority that manages biodiversity in the Galápagos archipelago. 2.2 Statistical analysis We first investigated the differences between C. marthae and C. subcristatus in their thermoregulatory niche, defined as the bivariate space composed by body temperature and UVB exposure (Fig. 2 ). We consider these two interdependent variables as the most representative of animals’ thermoregulation, as they reflect the environmental conditions that iguanas can select or tolerate to sustain their physiological temperature requirements. BodyT and UVB were thus set as the joint response in a bivariate GAM, including predictors concerning individual features ( species , sex , and mass ), the time of the day ( time ) and environmental conditions at each sighting event ( airT and UVB max ). Prior to model fitting, we assessed pairwise Pearson correlations and excluded multicollinearity as a potential issue ( r < 0.4 for each pairwise combination; Table S1 ). Body mass is expected to influence rates of heat exchange between animals and their environment (Dzialowski & O’Connor, 1999 ; Giacometti et al., 2023 ) and has been reported to differ both between species ( C. subcristatus is usually larger than C. marthae ) and between sexes (adult males are generally larger than females) (Gentile 2012 ). The hour of sightings was included to account for daily variations in both body temperature (Firth & Belan, 1998 ) and UVB exposure (Ferguson et al., 2010 ), as it reflects the time iguanas could have spent in basking before measurements. Finally, air temperature and maximum UVB irradiance were included in the model to represent the environmental conditions available for iguanas’ thermoregulation. Time was set as a smooth term, as we hypothesized that this variable has a non-linear relationship with the joint response. AirT and UVB max were included as a tensor product smooth interaction (hereafter referred to as airT - UVB max tensor), accounting for both the main and the joint effects of such terms on the response. In order to evaluate whether the effects of environmental conditions and daily variation differed between species, we tested for differences in smooth terms between species. To do so, we fitted four additional single-response GAMs for bodyT and UVB : a baseline model with common smooth effects for both airT - UVB max tensor and time for the two species, and three alternative models with species-dependent smooths for the airT - UVB max tensor, time , or both. We then selected the best model based on likelihood ratio tests (LRTs), assessing whether species-dependent smooths significantly improved model fit, and included the selected terms in the final bivariate model. Concurvity values were checked to detect potential nonlinear dependencies among smooth terms (Table S2). GAMs were fitted with the “mgcv” package (Wood & Wood, 2015 ) using data from 56 C. marthae (21 females and 35 males) and 55 C. subcristatus (24 females and 31 males). We tested for interspecific differences microhabitat selection, measured as the animal’s position in relation to natural shelters. Because only a few individuals were observed in thein “shade” category (5 C. marthae and 4 C. subcristatus ), the categories “shade” and “partial shade” were pooled into a single category. The resulting microhabitat variable therefore comprised two levels: “shade” (33 C. marthae and 17 C. subcristatus ) and “sun” (37 C. marthae and 44 C. subcristatus ). We modelled the probability of iguanas to be sighted in the “sun” microhabitat category using a GAM with a binomial error distribution and logit link function, including species , sex , and mass as predictors. Time was included as a smooth term to account for diel variation in microhabitat use related to thermoregulation. To assess whether the effect of time on microhabitat use differs between species, we compared models with common and species-dependent smooth effects by using likelihood ratio tests (LRTs) testing whether a separate smooth of time for the two species significantly improved model fit. All analyses were performed in R v4.1.2 (R Core Team, 2021 ) running within R-Studio v2023.03.1 + 446 (Posit Team, 2023 ). 3. Results 3.1 Thermoregulatory strategies Data on bodyT and UVB provide a preliminary description of pink and yellow iguanas’ thermoregulatory niches, with C. marthae displaying higher densities at lower UVB values than C. subcristatus (Fig. 2 ). Differences between the two species were formally evaluated using GAMs. Model selection through LRTs indicated a significant improvement in model fit when including a species-dependent smooth for the airT - UVB max tensor for the UVB response only ( p = 0.043). By contrast, the interaction between species and the airT - UVB max tensor for the bodyT , as well as the interactions between species and time for both responses, did not significantly enhance model fit and were therefore excluded from the final GAM (Table S3). The best model thus highlighted a differential effect of the airT-UVB max tensor on the UVB response between the two species (Table 1 ). In particular, C. marthae and C. subcristatus expose themselves at similar UVB levels when the maximum solar irradiance is less than approximately 300 µWatt/cm 2 . At higher levels of UVB max , pink iguanas tend to be found at lower UVB values than yellow iguanas (Fig. 3 ). Our bivariate GAM did not retrieve any differences in bodyT between pink and yellow iguanas. By predicting the trends of airT and UVB max throughout the day, we estimated the daily variation of bodyT and UVB for the two species. Iguanas’ body temperature increases throughout the morning, reaching a plateau at approximately 35°C around 11:30 am, which is maintained until the end of the sampling period (Fig. 4 A). The daily variation in UVB exposure generally displays an increase during the morning followed by a decrease after midday for both species. However, while C. subcristatus roughly follows a quadratic trend, reaching a peak of UVB amounting to ca. 300 µWatt/cm² at approx. 12:00 pm, C. marthae UVB exposure increases in the early morning, stabilizes at around 230 µWatt/cm² between 10:00 am and 12:00 pm, and subsequently decreases in the afternoon (Fig. 4 B). Table 1 Model coefficients estimated for the two responses, namely body temperature and UVB exposure, set as dependent variables in a bivariate Generalized Additive Model (GAM). Estimated model values (Estimate), standard errors (SE), and p-values ( p ) for linear predictors (Term) are reported for each separate response. Effective degrees of freedom (edf), Chi-squared statistics (Chisq) and p -values ( p ) are shown to report the approximate significance of smooth terms. Body temperature Term Estimate SE p Intercept 34.438 1.244 Species C. subcristatus -0.916 0.606 0.131 SexMale -0.942 0.627 0.133 Mass -0.104 0.254 0.683 Approximate significance of smooth terms Smooth term edf Chisq p airT, UVB max 3.141 26.651 < 0.001 Time 2.375 19.673 < 0.001 UVB exposure Term Estimate SE p Intercept 236.776 414.649 Species C. subcristatus 408.590 201.054 0.042 SexMale 162.779 211.018 0.441 Mass -130.705 85.365 0.126 Approximate significance of smooth terms Smooth term edf Chisq p airT, UVB max:Species C. marthae 4.898 30.801 < 0.001 airT, UVB max:Species C. subcristatus 3.000 34.233 < 0.001 Time 3.097 11.542 0.018 3.2 Microhabitat use LRT results indicate that the interaction between time and species did not provide a significant improvement in model fit, and thus it was excluded from the final GAM (Table S4). We detected a significant difference between the two species ( p = 0.046) in the probability of occupying the two categories of microhabitat (Table S5). Specifically, C. marthae has a lower probability of being found in sunny sites compared to C. subcristatus , and consequently greater chances to occupy shady sites. Both species tend to occupy different microhabitats throughout the day (approximate significance of the smooth term for time : p = 0.011). The probability of being found in “sun” is highest in the early morning ( ca. 0.95 for C. subcristatus and 0.85 for C. marthae ) and decreases until about 2:00 pm ( ca. 0.55 for C. subcristatus and 0.35 for C. marthae ), followed by a slightly increasing trend in the afternoon (Fig. 5 ). Discussion Thermoregulation in reptiles depends on a wide range of factors, such as physiological requirements, behavior, body traits, and environmental conditions (Seebacher & Franklin, 2005 ; Stuart-Fox et al., 2017 ; Giacometti et al., 2023 ). In this study, we investigated the differences in thermoregulatory strategies between two land iguanas living in syntopy on Wolf Volcano (Isabela Island, Galápagos). The two congeneric species display very distinct colorations, with C. marthae exhibiting large portions of unpigmented skin and C. subcristatus showing yellowish-brownish coloration. Our results revealed a difference in the thermoregulation strategies between syntopic pink and yellow iguanas, highlighting also the role of microhabitat features in modulating their exposure to solar radiation. The two species significantly differ in the UVB levels at their sighting locations, with pink iguanas being found at lower UVB values. Specifically, such differences increase when the maximum environmental solar irradiance exceeds approx. 300 µWatt/cm 2 , whereas under conditions of lower UVB max , the two species tend to be exposed to comparable UVB levels. The daily trend of UVB exposure thus varies between the two species. While the trend of yellow iguanas generally follows the maximum solar irradiance available ( i.e. , a rough quadratic relation between time and UVB max , with the highest peak at around 12:00 pm), pink iguanas are exposed to relatively constant UVB intensities from approx. 10:00 am to 12:00 pm. Therefore, our results suggest that the two species regulate their UVB exposure differently, with pink iguanas exhibiting active avoidance of high solar irradiance. Supporting this evidence, we detected a significant difference in the use of microhabitat features. Although the two species display similar trends throughout the day, the estimated probability of being found in sunny and shady spots significantly vary between C. marthae and C. subcristatus . Specifically, yellow iguanas have a higher probability of occupying open sites than pink iguanas, which, by contrast, have a stronger tendency to select spots with bushes and/or trees that guarantee opportunities for shading. These findings corroborate the previous results indicating that pink iguanas usually occupy areas with higher normalized difference vegetation index (NDVI) compared to yellow iguanas on the top of Wolf Volcano (Gargano et al., 2022 ). The avoidance of high levels of solar radiation observed in pink iguanas may be related to the peculiar histological structure of the depigmented skin in this species. Indeed, skin pigmentation provides protective functions against excessive exposure to solar radiation, which may negatively affect both reptiles’ health and reproductive success. The study area is in proximity to the Equator at about 1500–1650 m asl, where the UVB irradiance is extremely high, up to 600 µW/cm 2 (Di Giacomo et al., 2022 ). Therefore, the partially pigmented C. marthae may avoid prolonged exposure at elevated UVB levels to prevent excessive DNA damage risk. Intriguingly, despite the observed difference in patterns of exposure to solar radiation, the body temperatures of the two species are similar. Because of the extremely difficult logistics of the site that does not allow long permanence, we could not conduct focal animal samplings to allow the recording of time spent at basking by single individuals. However, it is quite likely that the difference in the histological skin features between the two species may be associated with differences in basking time, and that the combination of the two could help maintaining similar body temperatures. The large capillary aggregates in the dermis of pink iguanas, absent in yellow ones (Lewbart et al., 2023 ), may support more efficient heat exchange, allowing for faster warming or cooling. Although dark colored individuals heat faster than lighter ones (Clusella-Trullas et al., 2009 ), these vascular specializations could allow pink iguanas to achieve body temperatures comparable to yellow iguanas, while limiting their exposure to harmful UVB levels, potentially reducing DNA damage risk. Indeed, body temperature control of squamates is strongly associated with the activity of their circulatory system, primarily concerning heart rates and peripheral blood flows (Dzialowski & O’Connor, 1999 ; Seebacher, 2000 ; Porter & Witmer, 2015 ). For example, it was observed that dermal blood flow in reptiles generally intensifies during warming (Rice & Bradshaw, 1980 ; Dzialowski & O’Connor, 2001 ), which is expected to occur primarily by conduction, convection and radiation (Gates, 1980; Fei et al., 2012 ). In balanced vasodilation and contraction, the large aggregates of dermal capillaries observed in the pink iguana may increase the flow of warmed blood to the core, enhancing its heating rate and allowing pink iguanas to warm up faster compared to yellow ones. Similarly, the superficial vascular network can also contribute rapid radiation to prevent overheating, if needed. This process could be particularly efficient if mediated by a behavior that could allow a rapid switch from heating to cooling, such as an active avoidance of excessive solar radiation. Indeed, contrary to the yellow iguanas, the pattern of exposure to UVB during the day would indicate that pink iguanas minimize their exposure to high amounts of UVB irradiance, conducting their activities in more sheltered environments. Nevertheless, targeted experiments on exposure time and heating rates are required to clarify these mechanisms. By modelling the daily variation of body temperature in the two species, we observed a rather fast increase during the morning followed by a plateau for the rest of the day. When compared with the daily trend in air temperature, this pattern indicates that iguanas effectively thermoregulate to both reach and maintain their body temperature while avoiding overheating (see Taylor et al., 2020). The preferred external body temperature estimated for both species is approximately 35°C, which is consistent with previous data on Galápagos land iguanas (Christian et al., 1983 ; see Valle et al., 2019 ). Although internal body temperature may differ from external temperature, previous studies have shown a strong correlation between dorsal body temperature measured via infrared radiation and cloacal temperature in reptiles (Barroso et al., 2016 ), and this has also been confirmed for Galápagos iguanas (Valle et al., 2019 ). Moreover, it is reasonable to assume that the discrepancy between internal and external temperatures is similar in pink and yellow iguanas. Therefore, while further studies are required to fully understand the regulation of the internal body temperatures of the two species, our results suggest that they have similar requirements in terms of body temperature. Comprehensively, our study revealed differences in thermoregulatory strategies between the two congeneric iguanas occurring in syntopy on the top of Wolf Volcano. Pink iguanas have a stronger tendency to avoid excessive exposure to solar radiation than yellow iguanas, likely to be related to the lack of photoprotective pigments in several areas of the skin. Since the description of the species, the peculiar characteristics of pink iguanas’ skin raised questions about their possible selective advantage or disadvantage. Preliminary results (Gentile et al., in prep ) would suggest that the higher documented damage observed at nDNA in erythrocytes (Gustavino et al., 2014 ) may impact on the lifespan of red cells, inducing an increased erythropoietic effort in the pink iguana at cost of other functions (growth and reproduction). Interestingly, the utilization of areas with dense vegetation on the top of Wolf Volcano, likely due to a more efficient use of irradiance in terms of heating and aimed at the reduction of overexposure to UVB, could justify the significantly lower concentrations of vitamin D in plasma samples of pink iguanas, compared to other Conolophus species (Di Giacomo et al., 2022 ). Although further functional studies are needed, these histological characteristics may suggest a selective advantage related to thermoregulation. In this context, genomic data offer an additional layer of interpretation. In a recent study of iguana genomes (Lopez-Delgado et al., 2025), Gene Ontology (GO) terms associated with developmental pigmentation processes were significantly overrepresented in the pink iguana, compared to the other Galápagos iguanas, supporting an evolutionary emphasis on pigmentation pathways. Furthermore, in the pink iguana, signatures of positive selection were detected in several transcription factors and signaling genes that interact with or regulate the microphthalmia-associated transcription factor (MITF), a master regulator of melanocyte development and pigment cell differentiation (Lopez-Delgado et al., 2025). The difference in thermoregulation strategies, likely mediated by skin characteristics, may represent a factor promoting the coexistence between the two species, specifically in terms of microhabitat selection. Indeed, we hypothesize that pink iguanas could preferentially occupy areas with higher vegetation coverage compared to yellow ones, in order to maximize their chance to use shelter and shaded positions and avoid extreme UVB irradiance. However, other aspects may be reasonably involved in the observed microhabitat differentiation between the two species, and further studies on both species’ ecological requirements ( e.g. , trophic needs, mating behavior) and interspecific relations are necessary to clarify this aspect. From a conservation perspective, understanding the mechanisms regulating both microhabitat selection and intraspecific coexistence is fundamental to plan future management practices. As reported in the Conservation and Management Plan 2022–2027 (CAMP) for the pink iguana (Rueda et al., 2023 ), the GNPD is considering the implementation of a head-start program and evaluating the feasibility of translocation actions. Based on our results, we recommend that management authorities consider the importance of habitat features related to the thermoregulatory requirements of pink iguanas when designing future practices to efficiently preserve the species. Overall, these findings highlight the importance of integrating physiological and behavioral ecology into conservation planning. The case of pink iguanas offers a compelling example of how distinct adaptive traits can mediate species coexistence and persistence in challenging environments, providing broader insights into reptilian responses to extreme ecological pressures. Declarations Conflicts of interest The authors declare that they have no competing interests. Ethics approval Not applicable. Consent to participate Not applicable. Consent for publication Not applicable. Funding This work was supported by the Mohamed Bin Zayed Fund, which provided a grant to GG (Project No. 12254183; https://www.speciesconservation.org/case-studies-projects/galapagos-pink-land-iguana/4183 ), and by RomaTre University funds, which were granted to MC and LV. Author contributions LG conceived the analytical approach, analyzed the data, and wrote the first draft of the manuscript. MG assisted with data handling, analyses, and manuscript revisions. PG and SM contributed to the design of the analyses and provided critical revisions. GC contributed to the interpretation of the analyses and provided critical revisions. CS acted as scientific coordinator for the research group at GNP and supported field activities. LV and MC contributed funding and provided comments on the manuscript. GG conceived the project, collected the data, supervised the analyses, revised the manuscript, and secured funding. All authors approved the final version of the manuscript. Acknowledgements This project is part of a long-term institutional agreement between the University Tor Vergata and the Galápagos National Park Directorate, aimed at the conservation of Galápagos iguanas. The authors would like to express their gratitude to the personnel of Galápagos National Park for their invaluable support. We gratefully thank Michela Onorati and Livia Di Giambattista for participating in data collection. The authors are grateful to Dr. Folco Giomi for his constructive feedback and insightful suggestions on the data analysis, which greatly contributed to the interpretation of the results. Availability of data and material The data that supports the findings of this study are available in the supplementary material of this article. References Aguilar R, Cruz FB (2010) Refuge use in a Patagonian nocturnal lizard, Homonota darwini : the role of temperature. 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Springer, Berlin Heidelberg Wood S, Wood MS (2015) Package ‘mgcv’. R package version 1(29):729 Supplementary Files SupplementaryIguanasbodytemperatureandUVBOecologia.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 02 Mar, 2026 Reviewers invited by journal 02 Mar, 2026 Editor assigned by journal 18 Nov, 2025 First submitted to journal 14 Nov, 2025 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-8116905","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":599240381,"identity":"53ea2a00-9550-4103-93a7-05e0549f6c36","order_by":0,"name":"Lorenzo Garizio","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-9215-1847","institution":"University of Rome Tor Vergata: Universita degli Studi di Roma Tor Vergata","correspondingAuthor":true,"prefix":"","firstName":"Lorenzo","middleName":"","lastName":"Garizio","suffix":""},{"id":599240382,"identity":"7813da5f-eeff-400c-a82d-4b797691f21e","order_by":1,"name":"Marco Gargano","email":"","orcid":"","institution":"Polytechnic University of Marche: Universita Politecnica delle Marche","correspondingAuthor":false,"prefix":"","firstName":"Marco","middleName":"","lastName":"Gargano","suffix":""},{"id":599240383,"identity":"9cd8db91-ecb3-4cf9-93fb-a340597479b8","order_by":2,"name":"Paolo Gratton","email":"","orcid":"","institution":"Universita degli Studi di Roma Tor Vergata Dipartimento di Biologia","correspondingAuthor":false,"prefix":"","firstName":"Paolo","middleName":"","lastName":"Gratton","suffix":""},{"id":599240384,"identity":"2998c506-ece3-4617-a3cd-37064475e108","order_by":3,"name":"Silvio Marta","email":"","orcid":"","institution":"Institute of Geosciences and Earth Resources National Research Council: Istituto di Geoscienze e Georisorse Consiglio Nazionale delle Ricerche","correspondingAuthor":false,"prefix":"","firstName":"Silvio","middleName":"","lastName":"Marta","suffix":""},{"id":599240385,"identity":"016df64f-66be-4395-8b31-0c35da4e6f3b","order_by":4,"name":"Giuliano Colosimo","email":"","orcid":"","institution":"University of Rome Tor Vergata: Universita degli Studi di Roma Tor Vergata","correspondingAuthor":false,"prefix":"","firstName":"Giuliano","middleName":"","lastName":"Colosimo","suffix":""},{"id":599240386,"identity":"a236a79b-7f98-430f-8d27-d87a4d2b33fd","order_by":5,"name":"Christian Sevilla","email":"","orcid":"","institution":"Galapagos National Park","correspondingAuthor":false,"prefix":"","firstName":"Christian","middleName":"","lastName":"Sevilla","suffix":""},{"id":599240387,"identity":"616a31fc-1172-4e54-9696-c03131f161cd","order_by":6,"name":"Leonardo Vignoli","email":"","orcid":"","institution":"Roma Tre University: Universita degli Studi Roma Tre","correspondingAuthor":false,"prefix":"","firstName":"Leonardo","middleName":"","lastName":"Vignoli","suffix":""},{"id":599240388,"identity":"ee4c8615-693a-46ad-93fe-5bc718a12f7e","order_by":7,"name":"Monica Carosi","email":"","orcid":"","institution":"Roma Tre University: Universita degli Studi Roma Tre","correspondingAuthor":false,"prefix":"","firstName":"Monica","middleName":"","lastName":"Carosi","suffix":""},{"id":599240389,"identity":"2e528da5-a29b-4f6b-aefa-c020aa87352c","order_by":8,"name":"Gabriele Gentile","email":"","orcid":"","institution":"University of Rome Tor Vergata: Universita degli Studi di Roma Tor Vergata","correspondingAuthor":false,"prefix":"","firstName":"Gabriele","middleName":"","lastName":"Gentile","suffix":""}],"badges":[],"createdAt":"2025-11-14 16:32:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8116905/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8116905/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104178397,"identity":"1f134567-7f98-49a7-b64e-338c02cbfc0d","added_by":"auto","created_at":"2026-03-08 16:54:54","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":45727,"visible":true,"origin":"","legend":"\u003cp\u003eMap of the Galápagos archipelago, Ecuador. The inset highlights the Wolf Volcano area, in the north of Isabela Island, with grey contour lines representing 400 m altitudinal changes. The red polygon corresponds to the Minimum Convex Polygon (MCP) of all \u003cem\u003eConolophus marthae \u003c/em\u003eknown occurrence points. The study area (in blue) is the MCP of both \u003cem\u003eC. marthae \u003c/em\u003eand \u003cem\u003eC. subcristatus\u003c/em\u003e sightings used for the analyses presented in this study (see Materials and Methods for details).\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8116905/v1/9a0bb356c719ec85c5e43103.jpg"},{"id":104178395,"identity":"2d83b389-3257-4ddf-9dec-8fe9e99bd39f","added_by":"auto","created_at":"2026-03-08 16:54:54","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":74757,"visible":true,"origin":"","legend":"\u003cp\u003eThe thermoregulatory niche, \u003cem\u003ei.e.\u003c/em\u003e, the bivariate space including body temperature values (\u003cem\u003ebodyT\u003c/em\u003e) and UVB levels at sighting positions (\u003cem\u003eUVB\u003c/em\u003e), of \u003cem\u003eC. marthae \u003c/em\u003e(in red) and \u003cem\u003eC. subcristatus \u003c/em\u003e(in yellow). Points indicate the position of each individual in terms of its \u003cem\u003ebodyT \u003c/em\u003eand \u003cem\u003eUVB\u003c/em\u003e. Shaded areas report the bivariate kernel densities estimates (75%, 50%, and 25% kernel density contours) for the two species.\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8116905/v1/f882707743f46ade921eb2d1.jpg"},{"id":104178398,"identity":"de8c3104-3dd5-443c-a5c4-71a3d2353cb0","added_by":"auto","created_at":"2026-03-08 16:54:54","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":49433,"visible":true,"origin":"","legend":"\u003cp\u003eDifferences between \u003cem\u003eC. marthae \u003c/em\u003eand \u003cem\u003eC. subcristatus\u003c/em\u003e in the effect of the tensor product smooth interaction between the air temperature (\u003cem\u003eairT\u003c/em\u003e) and the maximum UVB irradiance in the environment (\u003cem\u003eUVB max\u003c/em\u003e). The background colors represent the difference in the predicted UVB exposure between pink and yellow iguanas (\u003cem\u003eΔUVB\u003c/em\u003e = \u003cem\u003eUVB\u003c/em\u003e\u003csub\u003e\u003cem\u003epink\u003c/em\u003e\u003c/sub\u003e – \u003cem\u003eUVB\u003c/em\u003e\u003csub\u003e\u003cem\u003eyellow\u003c/em\u003e\u003c/sub\u003e) in response to the environmental conditions. Positive values indicate environmental conditions (\u003cem\u003eUVB max\u003c/em\u003e and \u003cem\u003eAirT\u003c/em\u003e) under which \u003cem\u003eC. marthae\u003c/em\u003e is predicted to receive more \u003cem\u003eUVB\u003c/em\u003e than the other species, whereas negative values are associated with higher \u003cem\u003eUVB \u003c/em\u003eestimates for \u003cem\u003eC. subcristatus\u003c/em\u003e. Black lines report 50 µWatt/cm² changes in \u003cem\u003eΔUVB\u003c/em\u003e. Points indicate the position of \u003cem\u003eC. marthae \u003c/em\u003e(in red) and \u003cem\u003eC. subcristatus \u003c/em\u003e(in yellow) in the bivariate space composed by \u003cem\u003eairT\u003c/em\u003e and \u003cem\u003eUVB max\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8116905/v1/db7a792f230c5a49cf5f3025.jpg"},{"id":104404053,"identity":"091c6287-c080-4568-98ff-1fe433015739","added_by":"auto","created_at":"2026-03-11 12:19:39","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":103797,"visible":true,"origin":"","legend":"\u003cp\u003eDaily variations in body temperature (\u003cem\u003ebodyT\u003c/em\u003e, A) and UVB levels at sighting positions (\u003cem\u003eUVB\u003c/em\u003e; B) of \u003cem\u003eC. marthae \u003c/em\u003e(in red) and \u003cem\u003eC. subcristatus \u003c/em\u003e(in yellow). Lines represent the predicted trends of \u003cem\u003ebodyT\u003c/em\u003e and \u003cem\u003eUVB\u003c/em\u003e throughout the day, with shading areas reporting 95% Confidence Intervals. Predictions were obtained by evaluating the daily trends of air temperature (\u003cem\u003eairT\u003c/em\u003e)\u003cem\u003e \u003c/em\u003eand the maximum UVB irradiance in the environment (\u003cem\u003eUVB max\u003c/em\u003e), by additionally fitting Generalized Additive Models (GAMs) with \u003cem\u003eairT \u003c/em\u003eand \u003cem\u003eUVB max \u003c/em\u003eas separate responses and the hour of the day (\u003cem\u003etime\u003c/em\u003e) as smooth term predictor. Blue dashed lines indicate the predicted daily variation in \u003cem\u003eairT\u003c/em\u003e(A) and \u003cem\u003eUVB max\u003c/em\u003e (B) obtained from the respective GAMs.\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8116905/v1/d92cf8241eb833f600c11531.jpg"},{"id":104178394,"identity":"60c4797f-ce50-456d-9c3d-f4da3a3f6083","added_by":"auto","created_at":"2026-03-08 16:54:54","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":22595,"visible":true,"origin":"","legend":"\u003cp\u003eDetection probability of \u003cem\u003eC. marthae \u003c/em\u003e(in red) and \u003cem\u003eC. subcristatus \u003c/em\u003e(in yellow) in the two categories of \u003cem\u003emicrohabitat\u003c/em\u003e(“sun” and “shade”) estimated by fitting a generalized additive model (GAM) with binomial error distribution and logit link function. Lines illustrate how the probability of being detected in “shade” and “sun” varies during the day (\u003cem\u003etime\u003c/em\u003e) for both species. Shading areas represent 95% confidence intervals. Binned data are displayed as points, with point size proportional to the number of observations used for binning (\u003cem\u003eN\u003c/em\u003e).\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8116905/v1/b29d752479bdd0484768191e.jpg"},{"id":104408498,"identity":"2b411e68-6acf-4c17-b830-a9aeb4dfcd49","added_by":"auto","created_at":"2026-03-11 12:42:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1059867,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8116905/v1/2fb6f3d7-0898-4ede-9cfc-96970220da94.pdf"},{"id":104178418,"identity":"de2f3c1b-d033-4414-acba-d67cfb0b11fa","added_by":"auto","created_at":"2026-03-08 16:54:58","extension":"docx","order_by":10,"title":"","display":"","copyAsset":false,"role":"supplement","size":2543163,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryIguanasbodytemperatureandUVBOecologia.docx","url":"https://assets-eu.researchsquare.com/files/rs-8116905/v1/72d644653368ea9f5e611cdd.docx"}],"financialInterests":"","formattedTitle":"Thermoregulation in two syntopic Galápagos land iguanas: the role of microhabitat selection and skin pigmentation","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThermoregulation, \u003cem\u003ei.e.\u003c/em\u003e, the modulation of body temperature in response to environmental conditions, is a fundamental homeostatic biological process (Wieser, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Huey, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Angilletta et al., 2004). Ectothermic organisms cannot generate enough metabolic heat to maintain a body temperature significantly different from the surrounding environment. To thermoregulate, they have evolved a diverse range of behavioral and physiological adaptations (Hutchison \u0026amp; Maness, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e1979\u003c/span\u003e; Stevenson, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Seebacher, \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Non-avian reptiles (hereafter \u0026ldquo;reptiles\u0026rdquo;) possess a remarkable adaptability, enabling them to occupy a wide variety of habitats across the tropical and temperate regions (Roll et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Among the behavioral adaptations reptiles employ to regulate their body temperature, basking involves warming up by exposing the body to sun rays or warm surfaces, an activity that may take up a large fraction of their daily time budget (Gvožd\u0026iacute;k, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Basking reptiles adopt different strategies to modulate heat exchange; these include adjusting their position, posture, duration of exposure to sun rays, and selecting the appropriate basking surface (Seebacher, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Thermoregulatory behaviors additionally involve cooling strategies, such as avoidance of direct sunlight, selection of colder microhabitats and use of shelters (Aguilar \u0026amp; Cruz \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Grimm-Seyfarth et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Frequency and duration of basking are influenced by the physiological and structural constraints of each species (\u003cem\u003ee.g.\u003c/em\u003e, the body size) as well as the thermal conditions of their environment (Giacometti et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNon-behavioral traits also influence thermoregulation. For instance, skin coloration affects the efficacy of heat absorption from sun radiation. Indeed, dark-colored surfaces have lower reflectance than light-colored ones. Consequently, dark bodies absorb more solar radiation than lighter-colored bodies, resulting in higher heating rates. Therefore, skin pigmentation significantly influences thermoregulatory efficiency of ectotherms (Stuart-Fox et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In reptiles, differences in both heating rates and body temperature were observed between wildtypes and melanic morphs (Az\u0026oacute;car et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Clusella-Trullas et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Skin pigmentation also plays a role in responses to stress deriving from exposure to ultraviolet (UV) radiation (McNamara et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and melanin-based coloration seems to be associated with photoprotective functions (Kumaş et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Excessive exposure to UV radiation may lead to reptiles\u0026rsquo; skin and eye damage as well as diminished reproductive success (Ferguson et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Gardiner et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Nevertheless, exposure to sunlight is necessary for other physiological processes, such as the biosynthesis of vitamin D (Ferguson et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2002\u003c/span\u003e), which plays a crucial role in regulating calcium absorption, cell signaling and immune responses (Lips, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Boyan et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Bishop et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe thermal properties of the environment are among the main factors affecting the distribution of reptiles (Guisan \u0026amp; Hofer \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; McCain, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Indeed, thermoregulation requirements shape the habitat selection in reptiles, both at the macro- and microscale level (\u003cem\u003ee.g.\u003c/em\u003e, Row \u0026amp; Blouin-Demers, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Harvey \u0026amp; Weatherhead, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Gifford et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Complex environments with both sunny and shaded spots represent suitable habitats for many species, as they provide opportunities to regulate the exposure to solar radiation efficiently. For this reason, reptiles\u0026rsquo; occurrence is frequently associated with ecotones between open and vegetated areas (Madani et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Because microhabitat selection is related to thermoregulation requirements, the habitat usage by reptiles is influenced by both seasonality (Ortega \u0026amp; P\u0026eacute;rez-Mellado, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) and regional differences (Price-Rees et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Seasonal variations predominantly affect reptiles\u0026rsquo; microhabitat selection in temperate areas, where they usually select sun-exposed microhabitats, especially during colder periods, to warm up and reach suitable body temperatures (\u003cem\u003ee.g\u003c/em\u003e., Langkilde et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). By contrast, in tropical lowlands, where temperatures are higher throughout the year, reptiles can more easily maintain elevated body temperatures through thermoregulation. Consequently, habitat selection is more likely to be driven by the need to avoid overheating than by finding basking sites (Price-Rees et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Gal\u0026aacute;pagos pink land iguana (\u003cem\u003eConolophus marthae\u003c/em\u003e Gentile \u0026amp; Snell, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; hereafter \u0026ldquo;pink iguana\u0026rdquo;) is one of the most iconic terrestrial animals of the Gal\u0026aacute;pagos archipelago, and a flagship species for conservation (Gentile \u0026amp; Snell, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Gentile et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The only known population of pink iguanas occurs in tropical dry shrublands and tropical dry forests on the top and northern slopes of Wolf Volcano on Isabela Island (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The adult population size of the pink iguana amounts to only \u003cem\u003eca.\u003c/em\u003e 200 individuals (Garizio et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) occupying an extremely limited range (\u003cem\u003eca.\u003c/em\u003e 42 Km\u003csup\u003e2\u003c/sup\u003e; Gargano et al., \u003cem\u003esubmitted.\u003c/em\u003e). For this reason, the species has been classified as \u0026ldquo;critically endangered\u0026rdquo; in the IUCN Red List (Gentile, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Since its description, the peculiar coloration of \u003cem\u003eC. marthae\u003c/em\u003e has prompted questions on its evolutionary and ecological significance. The head and a large portion of the body of the species appear pink, as well as the anterior legs; the middle-posterior part of the body typically presents a black-striped pattern, whereas the tail and the posterior legs are black (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e; Gentile \u0026amp; Snell, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). The extension of pink and black portions can vary between individuals. This color pattern is unique within the Iguanidae, including those inhabiting the Gal\u0026aacute;pagos archipelago. Marine iguanas (\u003cem\u003eAmblyrhynchus cristatus\u003c/em\u003e) generally display a dark coloration, whereas Gal\u0026aacute;pagos land iguanas (\u003cem\u003eC. subcristatus\u003c/em\u003e, hereafter \u0026ldquo;yellow iguana\u0026rdquo;) and Barrington land iguanas (\u003cem\u003eC. pallidus\u003c/em\u003e) both exhibit yellowish-brownish colorations (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Histological analysis of skin samples showed that the pink areas of \u003cem\u003eC. marthae\u003c/em\u003e are associated with a complete lack of pigmentary cells, whereas melanocytes occur in the skin of \u003cem\u003eC. subcristatus\u003c/em\u003e and are particularly abundant in \u003cem\u003eA. cristatus\u003c/em\u003e (Lewbart et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2023\u003c/span\u003e, Scimeca et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Moreover, the stratum laxum of the pink iguana\u0026rsquo;s dermis displays a complex network of large capillaries, absent in the other Gal\u0026aacute;pagos iguana species (Lewbart et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Ultimately, the pink color of pink iguanas is not due to a pigment, but in fact caused by blood flowing through abundant, connected vascular channels in the stratum laxum, which lacks protective melanophores.\u003c/p\u003e \u003cp\u003ePrevious research (Gustavino et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) reported elevated nuclear DNA (nDNA) damage in the erythrocytes of pink iguanas, likely due to high exposure to UVB radiation, along with lower vitamin D levels compared to other Gal\u0026aacute;pagos species (Di Giacomo et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Since skin pigmentation plays a key role in both photoprotection (McNamara et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and thermoregulation (Stuart-Fox et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), differences in coloration may drive species-specific basking behaviors and thermal strategies. The lack of photoprotective pigments in its skin may impact \u003cem\u003eC. marthae\u003c/em\u003e\u0026rsquo;s tolerance to intense solar radiation, promoting behavioral avoidance of peak sun exposure. As a result, \u003cem\u003eC. marthae\u003c/em\u003e could experience reduced thermoregulatory efficiency and suboptimal body temperatures compared to the syntopic population of \u003cem\u003eC. subcristatus\u003c/em\u003e on Wolf Volcano. Alternatively, the two species may adopt different thermoregulatory strategies, relying on different daily activity patterns, microhabitat preferences, or behavioral adjustments that reflect divergent responses to the same environmental conditions. From this perspective, the syntopic occurrence of \u003cem\u003eC. marthae\u003c/em\u003e and \u003cem\u003eC. subcristatus\u003c/em\u003e on Wolf Volcano offers a unique opportunity to test these hypotheses by comparing their thermal ecology and habitat use. Specifically, we hypothesize that the partial lack of photoprotective pigments in \u003cem\u003eC. marthae\u003c/em\u003e\u0026rsquo;s skin leads to behavioral avoidance of intense solar radiation, resulting in a thermoregulatory niche that differs from that of \u003cem\u003eC. subcristatus\u003c/em\u003e. To evaluate this, we first analyzed data collected during monitoring activities to test for interspecific differences in thermoregulatory niche, defined as the bivariate space composed of body temperature and UVB exposure, by fitting Generalized Additive Models (GAMs). Furthermore, we hypothesized that differences in microhabitat use contribute to these patterns, with \u003cem\u003eC. marthae\u003c/em\u003e expected to occur more frequently in areas offering opportunities for shading. To test this, we modelled species occurrence associated with the presence of natural shelters linked to thermoregulation. We investigated the use of microhabitat features linked to thermoregulation by fitting a binomial GAM to determine whether \u003cem\u003eC. marthae\u003c/em\u003e and \u003cem\u003eC. subcristatus\u003c/em\u003e occurrence differs in relation to the presence of natural shelters that provide opportunities for shading.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Sampling activities\u003c/h2\u003e \u003cp\u003eDuring two field campaigns conducted on the north-western slopes of Wolf Volcano in 2014 (15\u0026ndash;23 June) and 2016 (31 August \u0026ndash; 4 September), 69 \u003cem\u003eC. marthae\u003c/em\u003e (42 males and 27 females) and 59 \u003cem\u003eC. subcristatus\u003c/em\u003e (35 males and 24 females) individuals were captured. All data used for our analysis involve iguanas sighted in the northwestern portion of the Wolf Volcano rim, within an area of \u003cem\u003eca.\u003c/em\u003e 2 km\u003csup\u003e2\u003c/sup\u003e and ranging from about 1500 to 1650 m asl (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, inset). Mature pink and yellow iguanas congregate in this location for mating during the wet season, from January/February through August/September (Trueman \u0026amp; D'Ozouville, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Gentile et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Onorati et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Gargano et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), whereas recent evidence indicates that \u003cem\u003eC. marthae\u003c/em\u003e probably moves to lower areas during the dry season (Colosimo et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). GPS coordinates, hour of capture (\u003cem\u003etime\u003c/em\u003e), species (\u003cem\u003especies\u003c/em\u003e), sex (\u003cem\u003esex\u003c/em\u003e), snout-vent-length (\u003cem\u003eSVL\u003c/em\u003e, in cm), and body mass (\u003cem\u003emass\u003c/em\u003e, in kg) were recorded for each captured iguana. Given the difficult logistics of the area, we could not adopt focal animal sampling to record the time spent on thermoregulatory behaviors such as basking and sheltering. Nevertheless, a standardized protocol to obtain information on environmental conditions related to temperature and solar radiation at capture events (i.e., exact location and time of day) was applied. Through the employment of a Solarmeter\u0026reg; Model 6.2 Sensitive UVB Meter, we recorded the intensity of UVB irradiance at sighting position (\u003cem\u003eUVB\u003c/em\u003e). UVB was recorded by placing the sensor perpendicular to the iguana\u0026rsquo;s longitudinal axis (head\u0026ndash;tail) orienting it to create a 45-degree angle with the ground, selecting the body side most prominently exposed to sunlight. This positioning aligned the sensor surface with the direction of the incident solar radiation. For most of the sightings (n\u0026thinsp;=\u0026thinsp;111, out of 128), we also measured the maximum UVB irradiance (\u003cem\u003eUVB max\u003c/em\u003e) in the environment by pointing the UVB meter directly towards the sun. We measured the surface body temperature (\u003cem\u003ebodyT\u003c/em\u003e) of iguanas by means of an I-R Thermometer, and the air temperature in the shade (\u003cem\u003eairT\u003c/em\u003e) with an air thermometer. Finally, we collected data on the iguanas\u0026rsquo; position in relation to shelters, such as bushes and trees, in order to represent their microhabitat utilization in response to solar radiation. Such information was summarized in the categorical variable \u003cem\u003emicrohabitat\u003c/em\u003e, considering a 3-m radius buffer around the capture location of each iguana, where vegetation cover was assessed. This variable includes three levels: \u0026ldquo;shade\u0026rdquo;, when iguanas were sighted in completely shaded sites, (\u003cem\u003ei.e.\u003c/em\u003e, areas entirely covered by bushes and/or trees); \u0026ldquo;partial shade\u0026rdquo;, when sites had partial canopy cover; and \u0026ldquo;sun\u0026rdquo;, when iguanas were observed in open areas (lacking tree or shrub cover). Handling of animals was performed in accordance with the protocol approved by the Gal\u0026aacute;pagos National Park Directorate (GNPD), the governmental authority that manages biodiversity in the Gal\u0026aacute;pagos archipelago.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Statistical analysis\u003c/h2\u003e \u003cp\u003eWe first investigated the differences between \u003cem\u003eC. marthae\u003c/em\u003e and \u003cem\u003eC. subcristatus\u003c/em\u003e in their thermoregulatory niche, defined as the bivariate space composed by body temperature and UVB exposure (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). We consider these two interdependent variables as the most representative of animals\u0026rsquo; thermoregulation, as they reflect the environmental conditions that iguanas can select or tolerate to sustain their physiological temperature requirements. \u003cem\u003eBodyT\u003c/em\u003e and \u003cem\u003eUVB\u003c/em\u003e were thus set as the joint response in a bivariate GAM, including predictors concerning individual features (\u003cem\u003especies\u003c/em\u003e, \u003cem\u003esex\u003c/em\u003e, and \u003cem\u003emass\u003c/em\u003e), the time of the day (\u003cem\u003etime\u003c/em\u003e) and environmental conditions at each sighting event (\u003cem\u003eairT\u003c/em\u003e and \u003cem\u003eUVB max\u003c/em\u003e). Prior to model fitting, we assessed pairwise Pearson correlations and excluded multicollinearity as a potential issue (\u003cem\u003er\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.4 for each pairwise combination; Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Body mass is expected to influence rates of heat exchange between animals and their environment (Dzialowski \u0026amp; O\u0026rsquo;Connor, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Giacometti et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) and has been reported to differ both between species (\u003cem\u003eC. subcristatus\u003c/em\u003e is usually larger than \u003cem\u003eC. marthae\u003c/em\u003e) and between sexes (adult males are generally larger than females) (Gentile \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The hour of sightings was included to account for daily variations in both body temperature (Firth \u0026amp; Belan, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1998\u003c/span\u003e) and UVB exposure (Ferguson et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), as it reflects the time iguanas could have spent in basking before measurements. Finally, air temperature and maximum UVB irradiance were included in the model to represent the environmental conditions available for iguanas\u0026rsquo; thermoregulation. \u003cem\u003eTime\u003c/em\u003e was set as a smooth term, as we hypothesized that this variable has a non-linear relationship with the joint response. \u003cem\u003eAirT\u003c/em\u003e and \u003cem\u003eUVB max\u003c/em\u003e were included as a tensor product smooth interaction (hereafter referred to as \u003cem\u003eairT\u003c/em\u003e-\u003cem\u003eUVB max\u003c/em\u003e tensor), accounting for both the main and the joint effects of such terms on the response. In order to evaluate whether the effects of environmental conditions and daily variation differed between species, we tested for differences in smooth terms between species. To do so, we fitted four additional single-response GAMs for \u003cem\u003ebodyT\u003c/em\u003e and \u003cem\u003eUVB\u003c/em\u003e: a baseline model with common smooth effects for both \u003cem\u003eairT\u003c/em\u003e-\u003cem\u003eUVB max\u003c/em\u003e tensor and \u003cem\u003etime\u003c/em\u003e for the two species, and three alternative models with species-dependent smooths for the \u003cem\u003eairT\u003c/em\u003e-\u003cem\u003eUVB max\u003c/em\u003e tensor, \u003cem\u003etime\u003c/em\u003e, or both. We then selected the best model based on likelihood ratio tests (LRTs), assessing whether species-dependent smooths significantly improved model fit, and included the selected terms in the final bivariate model. Concurvity values were checked to detect potential nonlinear dependencies among smooth terms (Table S2). GAMs were fitted with the \u0026ldquo;mgcv\u0026rdquo; package (Wood \u0026amp; Wood, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) using data from 56 \u003cem\u003eC. marthae\u003c/em\u003e (21 females and 35 males) and 55 \u003cem\u003eC. subcristatus\u003c/em\u003e (24 females and 31 males).\u003c/p\u003e \u003cp\u003eWe tested for interspecific differences microhabitat selection, measured as the animal\u0026rsquo;s position in relation to natural shelters. Because only a few individuals were observed in thein \u0026ldquo;shade\u0026rdquo; category (5 \u003cem\u003eC. marthae\u003c/em\u003e and 4 \u003cem\u003eC. subcristatus\u003c/em\u003e), the categories \u0026ldquo;shade\u0026rdquo; and \u0026ldquo;partial shade\u0026rdquo; were pooled into a single category. The resulting \u003cem\u003emicrohabitat\u003c/em\u003e variable therefore comprised two levels: \u0026ldquo;shade\u0026rdquo; (33 \u003cem\u003eC. marthae\u003c/em\u003e and 17 \u003cem\u003eC. subcristatus\u003c/em\u003e) and \u0026ldquo;sun\u0026rdquo; (37 \u003cem\u003eC. marthae\u003c/em\u003e and 44 \u003cem\u003eC. subcristatus\u003c/em\u003e). We modelled the probability of iguanas to be sighted in the \u0026ldquo;sun\u0026rdquo; \u003cem\u003emicrohabitat\u003c/em\u003e category using a GAM with a binomial error distribution and logit link function, including \u003cem\u003especies\u003c/em\u003e, \u003cem\u003esex\u003c/em\u003e, and \u003cem\u003emass\u003c/em\u003e as predictors. \u003cem\u003eTime\u003c/em\u003e was included as a smooth term to account for diel variation in microhabitat use related to thermoregulation. To assess whether the effect of time on microhabitat use differs between species, we compared models with common and species-dependent smooth effects by using likelihood ratio tests (LRTs) testing whether a separate smooth of \u003cem\u003etime\u003c/em\u003e for the two species significantly improved model fit. All analyses were performed in R v4.1.2 (R Core Team, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) running within R-Studio v2023.03.1\u0026thinsp;+\u0026thinsp;446 (Posit Team, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Thermoregulatory strategies\u003c/h2\u003e \u003cp\u003eData on \u003cem\u003ebodyT\u003c/em\u003e and \u003cem\u003eUVB\u003c/em\u003e provide a preliminary description of pink and yellow iguanas\u0026rsquo; thermoregulatory niches, with \u003cem\u003eC. marthae\u003c/em\u003e displaying higher densities at lower UVB values than \u003cem\u003eC. subcristatus\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Differences between the two species were formally evaluated using GAMs. Model selection through LRTs indicated a significant improvement in model fit when including a species-dependent smooth for the \u003cem\u003eairT\u003c/em\u003e-\u003cem\u003eUVB max\u003c/em\u003e tensor for the \u003cem\u003eUVB\u003c/em\u003e response only (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.043). By contrast, the interaction between \u003cem\u003especies\u003c/em\u003e and the \u003cem\u003eairT\u003c/em\u003e-\u003cem\u003eUVB max\u003c/em\u003e tensor for the \u003cem\u003ebodyT\u003c/em\u003e, as well as the interactions between \u003cem\u003especies\u003c/em\u003e and \u003cem\u003etime\u003c/em\u003e for both responses, did not significantly enhance model fit and were therefore excluded from the final GAM (Table S3). The best model thus highlighted a differential effect of the \u003cem\u003eairT-UVB max\u003c/em\u003e tensor on the \u003cem\u003eUVB\u003c/em\u003e response between the two species (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In particular, \u003cem\u003eC. marthae\u003c/em\u003e and \u003cem\u003eC. subcristatus\u003c/em\u003e expose themselves at similar UVB levels when the maximum solar irradiance is less than approximately 300 \u0026micro;Watt/cm\u003csup\u003e2\u003c/sup\u003e. At higher levels of \u003cem\u003eUVB max\u003c/em\u003e, pink iguanas tend to be found at lower \u003cem\u003eUVB\u003c/em\u003e values than yellow iguanas (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Our bivariate GAM did not retrieve any differences in \u003cem\u003ebodyT\u003c/em\u003e between pink and yellow iguanas. By predicting the trends of \u003cem\u003eairT\u003c/em\u003e and \u003cem\u003eUVB max\u003c/em\u003e throughout the day, we estimated the daily variation of \u003cem\u003ebodyT\u003c/em\u003e and \u003cem\u003eUVB\u003c/em\u003e for the two species. Iguanas\u0026rsquo; body temperature increases throughout the morning, reaching a plateau at approximately 35\u0026deg;C around 11:30 am, which is maintained until the end of the sampling period (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). The daily variation in UVB exposure generally displays an increase during the morning followed by a decrease after midday for both species. However, while \u003cem\u003eC. subcristatus\u003c/em\u003e roughly follows a quadratic trend, reaching a peak of \u003cem\u003eUVB\u003c/em\u003e amounting to \u003cem\u003eca.\u003c/em\u003e 300 \u0026micro;Watt/cm\u0026sup2; at approx. 12:00 pm, \u003cem\u003eC. marthae\u003c/em\u003e UVB exposure increases in the early morning, stabilizes at around 230 \u0026micro;Watt/cm\u0026sup2; between 10:00 am and 12:00 pm, and subsequently decreases in the afternoon (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eModel coefficients estimated for the two responses, namely body temperature and UVB exposure, set as dependent variables in a bivariate Generalized Additive Model (GAM). Estimated model values (Estimate), standard errors (SE), and p-values (\u003cem\u003ep\u003c/em\u003e) for linear predictors (Term) are reported for each separate response. Effective degrees of freedom (edf), Chi-squared statistics (Chisq) and \u003cem\u003ep\u003c/em\u003e-values (\u003cem\u003ep\u003c/em\u003e) are shown to report the approximate significance of smooth terms.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003eBody temperature\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTerm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEstimate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntercept\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e34.438\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.244\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecies \u003cem\u003eC. subcristatus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-0.916\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.606\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.131\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSexMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-0.942\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.627\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.133\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMass\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-0.104\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.254\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.683\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003eApproximate significance of smooth terms\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmooth term\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eedf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eChisq\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eairT, UVB max\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.141\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26.651\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTime\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.375\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.673\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003eUVB exposure\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTerm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEstimate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntercept\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e236.776\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e414.649\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecies\u003cem\u003eC. subcristatus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e408.590\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e201.054\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.042\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSexMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e162.779\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e211.018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.441\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMass\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-130.705\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e85.365\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.126\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eApproximate significance of smooth terms\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmooth term\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eedf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eChisq\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eairT, UVB max:Species\u003cem\u003eC. marthae\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.898\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30.801\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eairT, UVB max:Species\u003cem\u003eC. subcristatus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34.233\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTime\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.097\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.542\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.018\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Microhabitat use\u003c/h2\u003e \u003cp\u003eLRT results indicate that the interaction between \u003cem\u003etime\u003c/em\u003e and \u003cem\u003especies\u003c/em\u003e did not provide a significant improvement in model fit, and thus it was excluded from the final GAM (Table S4). We detected a significant difference between the two species (\u003cem\u003ep\u0026thinsp;=\u003c/em\u003e\u0026thinsp;0.046) in the probability of occupying the two categories of \u003cem\u003emicrohabitat\u003c/em\u003e (Table S5). Specifically, \u003cem\u003eC. marthae\u003c/em\u003e has a lower probability of being found in sunny sites compared to \u003cem\u003eC. subcristatus\u003c/em\u003e, and consequently greater chances to occupy shady sites. Both species tend to occupy different microhabitats throughout the day (approximate significance of the smooth term for \u003cem\u003etime\u003c/em\u003e: \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.011). The probability of being found in \u0026ldquo;sun\u0026rdquo; is highest in the early morning (\u003cem\u003eca.\u003c/em\u003e 0.95 for \u003cem\u003eC. subcristatus\u003c/em\u003e and 0.85 for \u003cem\u003eC. marthae\u003c/em\u003e) and decreases until about 2:00 pm (\u003cem\u003eca.\u003c/em\u003e 0.55 for \u003cem\u003eC. subcristatus\u003c/em\u003e and 0.35 for \u003cem\u003eC. marthae\u003c/em\u003e), followed by a slightly increasing trend in the afternoon (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThermoregulation in reptiles depends on a wide range of factors, such as physiological requirements, behavior, body traits, and environmental conditions (Seebacher \u0026amp; Franklin, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Stuart-Fox et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Giacometti et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In this study, we investigated the differences in thermoregulatory strategies between two land iguanas living in syntopy on Wolf Volcano (Isabela Island, Gal\u0026aacute;pagos). The two congeneric species display very distinct colorations, with \u003cem\u003eC. marthae\u003c/em\u003e exhibiting large portions of unpigmented skin and \u003cem\u003eC. subcristatus\u003c/em\u003e showing yellowish-brownish coloration.\u003c/p\u003e \u003cp\u003eOur results revealed a difference in the thermoregulation strategies between syntopic pink and yellow iguanas, highlighting also the role of microhabitat features in modulating their exposure to solar radiation. The two species significantly differ in the UVB levels at their sighting locations, with pink iguanas being found at lower UVB values. Specifically, such differences increase when the maximum environmental solar irradiance exceeds approx. 300 \u0026micro;Watt/cm\u003csup\u003e2\u003c/sup\u003e, whereas under conditions of lower \u003cem\u003eUVB max\u003c/em\u003e, the two species tend to be exposed to comparable UVB levels. The daily trend of UVB exposure thus varies between the two species. While the trend of yellow iguanas generally follows the maximum solar irradiance available (\u003cem\u003ei.e.\u003c/em\u003e, a rough quadratic relation between \u003cem\u003etime\u003c/em\u003e and \u003cem\u003eUVB max\u003c/em\u003e, with the highest peak at around 12:00 pm), pink iguanas are exposed to relatively constant UVB intensities from approx. 10:00 am to 12:00 pm. Therefore, our results suggest that the two species regulate their UVB exposure differently, with pink iguanas exhibiting active avoidance of high solar irradiance. Supporting this evidence, we detected a significant difference in the use of microhabitat features. Although the two species display similar trends throughout the day, the estimated probability of being found in sunny and shady spots significantly vary between \u003cem\u003eC. marthae\u003c/em\u003e and \u003cem\u003eC. subcristatus\u003c/em\u003e. Specifically, yellow iguanas have a higher probability of occupying open sites than pink iguanas, which, by contrast, have a stronger tendency to select spots with bushes and/or trees that guarantee opportunities for shading. These findings corroborate the previous results indicating that pink iguanas usually occupy areas with higher normalized difference vegetation index (NDVI) compared to yellow iguanas on the top of Wolf Volcano (Gargano et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The avoidance of high levels of solar radiation observed in pink iguanas may be related to the peculiar histological structure of the depigmented skin in this species. Indeed, skin pigmentation provides protective functions against excessive exposure to solar radiation, which may negatively affect both reptiles\u0026rsquo; health and reproductive success. The study area is in proximity to the Equator at about 1500\u0026ndash;1650 m asl, where the UVB irradiance is extremely high, up to 600 \u0026micro;W/cm\u003csup\u003e2\u003c/sup\u003e (Di Giacomo et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Therefore, the partially pigmented \u003cem\u003eC. marthae\u003c/em\u003e may avoid prolonged exposure at elevated UVB levels to prevent excessive DNA damage risk.\u003c/p\u003e \u003cp\u003eIntriguingly, despite the observed difference in patterns of exposure to solar radiation, the body temperatures of the two species are similar. Because of the extremely difficult logistics of the site that does not allow long permanence, we could not conduct focal animal samplings to allow the recording of time spent at basking by single individuals. However, it is quite likely that the difference in the histological skin features between the two species may be associated with differences in basking time, and that the combination of the two could help maintaining similar body temperatures. The large capillary aggregates in the dermis of pink iguanas, absent in yellow ones (Lewbart et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), may support more efficient heat exchange, allowing for faster warming or cooling. Although dark colored individuals heat faster than lighter ones (Clusella-Trullas et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), these vascular specializations could allow pink iguanas to achieve body temperatures comparable to yellow iguanas, while limiting their exposure to harmful UVB levels, potentially reducing DNA damage risk. Indeed, body temperature control of squamates is strongly associated with the activity of their circulatory system, primarily concerning heart rates and peripheral blood flows (Dzialowski \u0026amp; O\u0026rsquo;Connor, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Seebacher, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Porter \u0026amp; Witmer, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). For example, it was observed that dermal blood flow in reptiles generally intensifies during warming (Rice \u0026amp; Bradshaw, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e1980\u003c/span\u003e; Dzialowski \u0026amp; O\u0026rsquo;Connor, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), which is expected to occur primarily by conduction, convection and radiation (Gates, 1980; Fei et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In balanced vasodilation and contraction, the large aggregates of dermal capillaries observed in the pink iguana may increase the flow of warmed blood to the core, enhancing its heating rate and allowing pink iguanas to warm up faster compared to yellow ones. Similarly, the superficial vascular network can also contribute rapid radiation to prevent overheating, if needed. This process could be particularly efficient if mediated by a behavior that could allow a rapid switch from heating to cooling, such as an active avoidance of excessive solar radiation. Indeed, contrary to the yellow iguanas, the pattern of exposure to UVB during the day would indicate that pink iguanas minimize their exposure to high amounts of UVB irradiance, conducting their activities in more sheltered environments. Nevertheless, targeted experiments on exposure time and heating rates are required to clarify these mechanisms.\u003c/p\u003e \u003cp\u003eBy modelling the daily variation of body temperature in the two species, we observed a rather fast increase during the morning followed by a plateau for the rest of the day. When compared with the daily trend in air temperature, this pattern indicates that iguanas effectively thermoregulate to both reach and maintain their body temperature while avoiding overheating (see Taylor et al., 2020). The preferred external body temperature estimated for both species is approximately 35\u0026deg;C, which is consistent with previous data on Gal\u0026aacute;pagos land iguanas (Christian et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1983\u003c/span\u003e; see Valle et al., \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Although internal body temperature may differ from external temperature, previous studies have shown a strong correlation between dorsal body temperature measured via infrared radiation and cloacal temperature in reptiles (Barroso et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), and this has also been confirmed for Gal\u0026aacute;pagos iguanas (Valle et al., \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Moreover, it is reasonable to assume that the discrepancy between internal and external temperatures is similar in pink and yellow iguanas. Therefore, while further studies are required to fully understand the regulation of the internal body temperatures of the two species, our results suggest that they have similar requirements in terms of body temperature.\u003c/p\u003e \u003cp\u003eComprehensively, our study revealed differences in thermoregulatory strategies between the two congeneric iguanas occurring in syntopy on the top of Wolf Volcano. Pink iguanas have a stronger tendency to avoid excessive exposure to solar radiation than yellow iguanas, likely to be related to the lack of photoprotective pigments in several areas of the skin. Since the description of the species, the peculiar characteristics of pink iguanas\u0026rsquo; skin raised questions about their possible selective advantage or disadvantage. Preliminary results (Gentile et al., \u003cem\u003ein prep\u003c/em\u003e) would suggest that the higher documented damage observed at nDNA in erythrocytes (Gustavino et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) may impact on the lifespan of red cells, inducing an increased erythropoietic effort in the pink iguana at cost of other functions (growth and reproduction). Interestingly, the utilization of areas with dense vegetation on the top of Wolf Volcano, likely due to a more efficient use of irradiance in terms of heating and aimed at the reduction of overexposure to UVB, could justify the significantly lower concentrations of vitamin D in plasma samples of pink iguanas, compared to other \u003cem\u003eConolophus\u003c/em\u003e species (Di Giacomo et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Although further functional studies are needed, these histological characteristics may suggest a selective advantage related to thermoregulation.\u003c/p\u003e \u003cp\u003eIn this context, genomic data offer an additional layer of interpretation. In a recent study of iguana genomes (Lopez-Delgado et al., 2025), Gene Ontology (GO) terms associated with developmental pigmentation processes were significantly overrepresented in the pink iguana, compared to the other Gal\u0026aacute;pagos iguanas, supporting an evolutionary emphasis on pigmentation pathways. Furthermore, in the pink iguana, signatures of positive selection were detected in several transcription factors and signaling genes that interact with or regulate the microphthalmia-associated transcription factor (MITF), a master regulator of melanocyte development and pigment cell differentiation (Lopez-Delgado et al., 2025).\u003c/p\u003e \u003cp\u003eThe difference in thermoregulation strategies, likely mediated by skin characteristics, may represent a factor promoting the coexistence between the two species, specifically in terms of microhabitat selection. Indeed, we hypothesize that pink iguanas could preferentially occupy areas with higher vegetation coverage compared to yellow ones, in order to maximize their chance to use shelter and shaded positions and avoid extreme UVB irradiance. However, other aspects may be reasonably involved in the observed microhabitat differentiation between the two species, and further studies on both species\u0026rsquo; ecological requirements (\u003cem\u003ee.g.\u003c/em\u003e, trophic needs, mating behavior) and interspecific relations are necessary to clarify this aspect. From a conservation perspective, understanding the mechanisms regulating both microhabitat selection and intraspecific coexistence is fundamental to plan future management practices. As reported in the Conservation and Management Plan 2022\u0026ndash;2027 (CAMP) for the pink iguana (Rueda et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), the GNPD is considering the implementation of a head-start program and evaluating the feasibility of translocation actions. Based on our results, we recommend that management authorities consider the importance of habitat features related to the thermoregulatory requirements of pink iguanas when designing future practices to efficiently preserve the species. Overall, these findings highlight the importance of integrating physiological and behavioral ecology into conservation planning. The case of pink iguanas offers a compelling example of how distinct adaptive traits can mediate species coexistence and persistence in challenging environments, providing broader insights into reptilian responses to extreme ecological pressures.\u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003e \u003cstrong\u003eConflicts of interest\u003c/strong\u003e \u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eEthics approval\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent to participate\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for publication\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by the Mohamed Bin Zayed Fund, which provided a grant to GG (Project No. 12254183; \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.speciesconservation.org/case-studies-projects/galapagos-pink-land-iguana/4183\u003c/span\u003e\u003cspan address=\"https://www.speciesconservation.org/case-studies-projects/galapagos-pink-land-iguana/4183\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e), and by RomaTre University funds, which were granted to MC and LV.\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eLG conceived the analytical approach, analyzed the data, and wrote the first draft of the manuscript. MG assisted with data handling, analyses, and manuscript revisions. PG and SM contributed to the design of the analyses and provided critical revisions. GC contributed to the interpretation of the analyses and provided critical revisions. CS acted as scientific coordinator for the research group at GNP and supported field activities. LV and MC contributed funding and provided comments on the manuscript. GG conceived the project, collected the data, supervised the analyses, revised the manuscript, and secured funding. All authors approved the final version of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis project is part of a long-term institutional agreement between the University Tor Vergata and the Gal\u0026aacute;pagos National Park Directorate, aimed at the conservation of Gal\u0026aacute;pagos iguanas. The authors would like to express their gratitude to the personnel of Gal\u0026aacute;pagos National Park for their invaluable support. We gratefully thank Michela Onorati and Livia Di Giambattista for participating in data collection. The authors are grateful to Dr. Folco Giomi for his constructive feedback and insightful suggestions on the data analysis, which greatly contributed to the interpretation of the results.\u003c/p\u003e\u003ch2\u003eAvailability of data and material\u003c/h2\u003e \u003cp\u003eThe data that supports the findings of this study are available in the supplementary material of this article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAguilar R, Cruz FB (2010) Refuge use in a Patagonian nocturnal lizard, \u003cem\u003eHomonota darwini\u003c/em\u003e: the role of temperature. 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R package version 1(29):729\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":"oecologia","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oeco","sideBox":"Learn more about [Oecologia](https://www.springer.com/journal/442)","snPcode":"442","submissionUrl":"https://submission.nature.com/new-submission/442/3","title":"Oecologia","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"thermal ecology, reptiles, GAM, UV radiation, habitat use","lastPublishedDoi":"10.21203/rs.3.rs-8116905/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8116905/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThermoregulation in reptiles depends on the interplay between environmental conditions, genetic adaptation and phenotypic plasticity. Behavioral strategies and skin pigmentation are among the main factors influencing the ability of reptiles to modulate heat transfer with the environment. The critically endangered Gal\u0026aacute;pagos pink land iguana (\u003cem\u003eConolophus marthae\u003c/em\u003e) displays a unique coloration, due to the absence of pigments across large portions of its body. In this study, we compared thermoregulatory strategies of \u003cem\u003eC. marthae\u003c/em\u003e and the syntopic population of yellow iguana (\u003cem\u003eC. subcristatus\u003c/em\u003e) on Wolf Volcano (Isabela Island, Gal\u0026aacute;pagos). While the two species display similar body temperatures, \u003cem\u003eC. marthae\u003c/em\u003e tends to expose itself to lower levels of ultraviolet B (UVB) irradiance. This difference reflects contrasting microhabitat use, with pink iguanas occupying shaded areas more frequently than yellow iguanas. The lack of photoprotective pigments in the pink iguana\u0026rsquo;s dermis may explain this behavior, as prolonged exposure to UV irradiance can be detrimental to iguana health. The avoidance of high solar radiation highlights the role of microhabitat features in meeting the thermoregulatory requirements of the pink iguana, which may preferentially select areas with denser vegetation that provides shelters and shade. Thus, the distinctive partial skin depigmentation of the pink iguana, which is otherwise interpretable as detrimental, may instead shape microhabitat selection, reduce competition, and ultimately facilitate coexistence with \u003cem\u003eC. subcristatus\u003c/em\u003e.\u003c/p\u003e","manuscriptTitle":"Thermoregulation in two syntopic Galápagos land iguanas: the role of microhabitat selection and skin pigmentation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-08 16:53:31","doi":"10.21203/rs.3.rs-8116905/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-03-02T12:13:21+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-02T11:06:40+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-18T12:01:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Oecologia","date":"2025-11-14T11:29:56+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"oecologia","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oeco","sideBox":"Learn more about [Oecologia](https://www.springer.com/journal/442)","snPcode":"442","submissionUrl":"https://submission.nature.com/new-submission/442/3","title":"Oecologia","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d8d6c239-8bc0-468a-946b-8cfacb2c908d","owner":[],"postedDate":"March 8th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-03-08T16:53:31+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-08 16:53:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8116905","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8116905","identity":"rs-8116905","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}