On the role of melanistic coloration on thermoregulation in the crepuscular geckoEublepharis macularius

Body coloration in ectotherms serves multiple biological functions, including avoiding predators, communicating with conspecific individuals, and involvement in thermoregulation. As ectotherms rely on environmental sources of heat to regulate their internal body temperature, stable melanistic body coloration or color change can be used to increase or decrease heat absorption and heat exchange with the environment. While the function of melanistic coloration for thermoregulation has been found to increase solar radiation absorption for heating in many diurnal ectotherms, research on crepuscular and nocturnal ectotherms is lacking. Since crepuscular and nocturnal ectotherms generally absorb heat from the substrate, coloration is likely under different selective pressures than in diurnal ectotherms. We tested if the proportion of dorsal melanistic body coloration is related to differences in body temperature heating and cooling rates in the crepuscular geckoEublepharis maculariusand whether changes in environmental temperature trigger color changes in this species. Temperature measurements of the geckos and of the environment were taken using infrared thermography and temperature loggers. Color data were obtained using objective photography and a newly developed custom software package. We found that body temperature reflected substrate temperatures, and that the proportion of melanistic coloration has no influence on heating or cooling rates or on color changes. These findings suggest that, inE. macularius, melanistic coloration may not be used for thermoregulation. Future research should further test the function of melanistic coloration in other crepuscular and nocturnal vertebrates to understand the evolution of melanistic pattern in animals active in low light conditions.