title: Color and Temperature Are Not Related in the Crepuscular Reptile, Eublepharis macularius
Creators: name: (:Unkn) Unknown
Publisher: name: George Mason University
Year: 2023
Subjects: subject: Thermoregulation
subject: Physiological color change
subject: Coloration
subject: Thermal melanism

description: Ectothermic organisms depend on external sources for heating and cooling to regulate their internal body temperature. Some ectotherms rely on physiological color change by adjusting melanistic body coloration to increase or decrease heat absorption. Furthermore, ectotherms with a greater proportion of stable melanistic body coloration seem to have better thermoregulatory performance in cold climates due to better absorption of solar energy to buffer body temperature in relation to environmental temperatures. Together with its influence on thermoregulation, body coloration is also used in ectotherms for other ecological functions, from escaping predators to communicating with conspecific individuals. As fluctuations in extreme temperatures due to global warming are becoming more frequent, understanding the relationship between coloration and suboptimal temperature is essential to predict the influence that this may have on other functions. In this study, we tested if the exposure to suboptimal low temperatures produces a physiological color in the crepuscular reptile Eublepharis macularius. Furthermore, we tested if the proportion of melanism on the body of these animals is related to differences in heating and cooling rates of the internal body temperature during suboptimal temperature exposure. Temperature measurements were taken using infrared photography and temperature loggers, and coloration was obtained using objective photography and analyzed using a newly developed custom software package. As the dorsal part of the body is the one mostly involved in physiological color changes in ectotherms, we tested if dorsal coloration would change as a response to lowering environmental temperatures, analyzing melanistic and non-melanistic areas of the body separately for twelve geckos. We expected a higher degree of color change in non-melanistic versus melanistic coloration and a relative higher average body temperature in geckos with a higher proportion of melanistic coloration. We found that body temperature reflects substrate temperatures, but that the proportion of melanistic coloration has a moderate negative correlation with cooling rates of body temperature. We also did not observe a relationship between body temperature and physiological color change for melanistic and non-melanistic color. These findings suggest that in E. macularius melanistic coloration may be used for other purposes such as predator avoidance and that physiological color change may not be used for thermoregulation to increase heat absorption, but may occur for background matching, similarly to what described for other nocturnal/crepuscular reptiles. Future research should further test these hypotheses to elucidate the function of melanistic coloration in crepuscular and nocturnal geckos and to understand the evolution of pattern development in organisms active in low light conditions.