Differences in thermoregulatory patterns between two syntopic Galápagos land iguanas (Conolophus marthae and C. subcristatus): the role of behavior and potential implications of distinct skin pigmentations

Thermoregulation in reptiles is a complex process affected by numerous factors, including both environmental conditions and animal adaptations. Behavioral and phenotypic traits such as pigmentation play a fundamental role in the ability of reptiles to modulate heat transfers with the environment. The critically endangered Galápagos pink land iguana (Conolophus marthae Gentile & Snell, 2009) displays a unique coloration, due to the absence of pigments in large portions of the body. In this study, we investigated the differences in thermoregulatory patterns between C. marthae and the syntopic C. subcristatus on the top of Wolf Volcano (Isabela Island, Galápagos). Whereas the two species display similar body temperatures, C. marthae tends to expose at lower ultraviolet B (UVB) radiation than the congeneric species. Such difference is mainly related to the distinct behaviors adopted by the two species. Specifically, pink iguanas have a higher tendency to avoid exposing their entire bodies to sun rays, preferring to occupy areas that allow them to maintain some body portions in the shade. The lack of photoprotective pigments in the pink iguana’s dermis may represent a key factor in explaining the observed difference between the two species, as the excessive exposure to UV radiation can be detrimental to iguanas’ health. The avoidance of high UVB radiation highlights the role of microhabitat features for the thermoregulatory requirements of pink iguanas. Moreover, differences in microhabitat selection may promote the coexistence between C. marthae and C. subcristatus, as pink iguanas could preferentially occupy areas with denser vegetation which guarantee more opportunities to use shelter and shaded sites.