Survey of melanistic garter snakes by traditional and geometric morphometries

Abstract

Melanism in garter snake populations is a rare and ecologically important occurrence. Melanism can be used to study the function of coloration and the process of genetic drift. Coloration patterns of garter snakes may affect fitness level, influenced by predation and thermal efficiency. It is therefore of interest how and why the melanistic trait is acquired. Along the Missouri river near Townsend, MT, three garter snake morphotypes are found; Thamnophis elegans, Thamnophis sirtalis, and melanistic individuals inhabit the area. While T. sirtalis and T. elegans are well studied, little is known about the melanistic population in this area. The goal of this study is to gain insight into which species the melanistic population belongs to and to gather information for further studies. A total of 81 T. elegans, 23 melanistic, and 20 T. sirtalis snakes were captured from March of 2007 to September of 2007. Morphotypes were compared using traditional and geometric morphometries. I discovered significant differences between T. sirtalis and melanistic morphotypes but less difference between T. elegans and melanistic morphotypes. I conclude that melanistic individuals in the Townsend area are morphometrically more similar to T. elegans than to T. sirtalis.