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Abstract. Models of snakes varying in color pattern have been used to test hypotheses about predation and mimicry. In the present study, clay models of the common garter snake were used to test for a difference in attack frequency between adult and juvenile striped and melanistic garter snakes; such difference may indicate a difference in cryptic coloration between the two morphs. The research was performed on the shores of Sandusky Bay and Lake Erie, where polymorphic garter snake populations contain both striped and melanistic garter snakes. There was no difference in attack frequency between the two morphs; however, juvenile snake models were attacked more frequently than adult ones. The study suggests that melanism may not confer a strong disadvantage with respect to visually-oriented predators.
OHIO J SCI 103 (3):62-66, 2003
INTRODUCTION
Color polymorphisms have significant implications for the ecology and evolution of animals because of the importance of color pattern in predator avoidance, physiology, thermoregulation, and intraspecific signaling. A striking form of polymorphism is found in the common garter snake, Thamnophis sirtalis. Throughout most of its extensive range, T. sirtalis has variable small dorsal "checkers" of tan, white, brown, and black, and sometimes yellow or orange, and a light-colored (ivory to yellow) dorsal stripe running most of the length of the body (see Conant and Collins 1998). In the Lake Erie region, melanism, or extremely dark epidermal coloration, is relatively prevalent (up to 59%, King 1988). Melanistic garter snakes are hypothesized to suffer greater predation than their striped counterparts (Gibson 1978; Gibson and Falls 1979, 1988; Lawson and King 1996). Melanistic snakes may appear less cryptic to predators because they lack disruptive coloration and contrast strongly against natural backgrounds found in the region. However, melanism may provide a thermal benefit which may enhance fitness (Gibson and Falls 1988; Bittner and others 2002). In this study, I used clay models of the common garter snake to test for a difference in attack frequency between adult and juvenile striped and melanistic garter snakes, which may indicate a difference in the level of ciyptic coloration (hereafter, crypsis) between the two morphs.
A systematic analysis of a large number of snake taxa concluded that the dorsal pigmentation patterns of snakes (for example, blotched, striped, banded) are strongly influenced...