Evidence for Phenotypic Plasticity in Snake Body Size and Relative Head Dimensions in Response to Amount and Size of Prey

Abstract

To test whether variation in body size and relative head dimensions may be a phenotypically plastic response to feeding experience in snakes, we assigned neonate water snakes, Nerodia sipedon, from four litters (n = 48) to two feeding treatment groups. One group was offered one large minnow twice weekly; the other group was offered two small minnows twice weekly. Body size (snout-vent length, mass) and head dimensions (head length, head width, jaw length, interocular distance) were measured at the beginning of the experiment and upon completion of the experiment 20 weeks later. Repeated-measures multivariate analysis of variance revealed significant effects of feeding treatment, sex, and family on change in body size. Repeated-measures MANCOVA (with body length as covariate) also revealed a significant effect due to family on change in head dimensions. The multivariate effect of feeding treatment on head dimensions approached statistical significance (P = 0.102); the univariate effect of feeding treatment was significant for jaw length (P = 0.010). Females increased in body size more than males did, and snakes offered large fish increased in body size and jaw length more than snakes offered small fish. These results suggest that body size and jaw length respond plastically to amount and size of prey.