Physiological Color Change in the Green Treefrog: Responses to Background Brightness and Temperature

Abstract

In an effort to better understand the function of physiological color change in anurans, we measured color change responses of the green treefrog, Hyla cinerea, to background brightness and temperature. We used our results to compare color and color change responses of males and females and to test two hypotheses for the function of physiological color change in anurans: (1) that color change serves to prevent detection by visual predators, and (2) that color change functions in thermoregulation or water balance. We found that (1) males are generally darker than females but the sexes exhibit similar color change responses, (2) treefrogs become lighter on brighter backgrounds, (3) treefrogs become lighter at higher temperatures, and (4) there is a background-by-temperature interaction such that color change responses to one variable depend on the level of the other. Our results suggest that color change may function both in predator avoidance and in thermoregulation or water balance. However, further investigations of color change responses to differently hued backgrounds, of the magnitude and biological significance of color-induced changes in body temperature and rates of evaporative water loss, and of color change in freeranging animals are needed.