EVIDENCE FOR PHENOTYPIC PLASTICITY IN SNAKE BODY-SIZE AND RELATIVE HEAD DIMENSIONS IN RESPONSE TO AMOUNT AND SIZE OF PREY

To test whether variation in body size and relative head dimensions ma y 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 l arge minnow twice weekly; the other group was offered two small minnow s twice weekly. Body size (snout-vent length, mass) and head dimension s (head length, head width, jaw length, interocular distance) were mea sured at the beginning of the experiment and upon completion of the ex periment 20 weeks later. Repeated-measures multivariate analysis of va riance revealed significant effects of feeding treatment, sex, and fam ily on change in body size. Repeated-measures MANCOVA (with body lengt h as covariate) also revealed a significant effect due to family on ch ange in head dimensions. The multivariate effect of feeding treatment on head dimensions approached statistical significance (P = 0.102); th e univariate effect of feeding treatment was significant for jaw lengt h (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 a nd jaw length respond plastically to amount and size of prey.