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

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 .