Meeting Abstract

1.7  Saturday, Jan. 4 09:30  Testing the thermal melanism hypothesis for lizards VAN DAMME, R*; VROONEN, J; Univ. of Antwerp, Belgium raoul.vandamme@ua.ac.be

Melanism is possibly the most common rarity in animal coloration. Starting with Kettlewell’s classic experiments on peppered moths, the phenomenon has received ample attention from evolutionary biologists, but the adaptive significance of melanism remains heavily debated. For heliothermic ectotherms, the popular thermal melanism hypothesis (TMH) holds that darker colors will result in faster heating, increasing the time available for activity near physiologically optimal body temperatures. This thermal benefit would give ectotherms a fitness edge, at least if attaining optimal body temperatures is difficult, and dark coloration does not increase the risk of predation too much. The empirical evidence for this idea is surprisingly meager. Here, we test a number of assumptions of the TMH for squamate reptiles, focusing on medium sized lizards. We measured shortwave absorptivity and heating rates in four insular populations of Podarcis melisellensis, two of which are melanic, one is dark brown, and one is of the normal greenish color. Using information on the lizards’ thermal preferences and local climatic conditions, we constructed two models to estimate the ecological significance of a darker skin. One model simply calculated the amount of time a lizard could reach its preferred body temperature range throughout the year and compared that among color types. A second model recognized that lizards will alternate basking bouts with spells of activity (e.g. foraging) which will bring them into thermally unfavorable microhabitats. It estimates the amount available for non-thermoregulatory activity and compares it among color types. The models suggest that the benefits of dark integuments are small for most of the activity period, but more substantial in spring.