Melanistic coloration does not influence thermoregulation in the crepuscular gecko Eublepharis 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 increases 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, in these
organisms melanistic coloration may have other primary functions besides
thermoregulation. As such, in this work, we hypothesized that the
proportion of dorsal melanistic body coloration would not influence
heating and cooling rates in the crepuscular gecko, Eublepharis
macularius, and that changes in environmental temperature would not
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 support that melanistic coloration
in E. macularius may not be used for thermoregulation and
strengthen the hypothesis that in animals active in low light conditions,
melanistic coloration may be used instead for camouflage or other
functions.