Ecogeographic Divergence Linked to Dorsal Coloration in Eastern Hog-Nosed Snakes (Heterodon platirhinos)

Abstract

Animal coloration can benefit fitness via its function in homeostatic regulation, communication, or camouflage. For wide-ranging taxa that are exposed to diverse climatic conditions throughout their range, spatial variation in color morphology might reflect locality-specific adaptive responses to those variable conditions. As a result, these species might vary in their color-climate associations over geographic space. Here, we integrate georeferenced photographs of adult animals with available bioclimatic data to test the hypothesis that dorsal color differences in Eastern Hog-Nosed Snakes (Heterodon platirhinos) reflect ecogeographic divergence. We first assigned each photographed snake into one of four dorsal color phases, namely, black, brown, red-orange, or yellow, and evaluated the spatial dispersion and bioclimatic niche occupancy of each phase by using multiple environmental niche modeling approaches. We then used pairwise comparisons of bioclimatic niche space to explicitly test for niche divergence among the color phases. Overall, black, brown, and red-orange phase H. platirhinos exploited different subsets of the species' geographic range and bioclimatic niche. In contrast, yellow phase snakes partly overlapped with red-orange and brown phase snakes in geographic and bioclimatic space. These findings support our hypothesis, and we discuss some of the possible functions of phase coloration.