Allometry of cranial morphology, gape size and ingestion performance in the banded watersnake (Nerodia fasciata) feeding on two types of prey

Abstract

Small body size imposes limitations on the feeding capabilities of juveniles, particularly in species that consume their prey whole. It has been hypothesized that juveniles exhibit exceptional performance measures to compensate for their small size. However, few studies have examined whether juveniles have better feeding performance relative to adults and investigations of snake feeding ontogeny have not shown enhanced performance in smaller snakes. I tested the hypothesis that juvenile snakes have better feeding performance by comparing maximum gape circumference and ingestion performance (time and number of pterygoid protractions) in a series of banded watersnakes (Nerodia fasciata) of different sizes fed fish and frogs. I also measured several external and osteological dimensions of the head and used Akaike's information criterion to determine which morphological measurements were the strongest predictors of relative gape. All skull measurements and maximum gape circumference showed negative allometry relative to snout-vent length (SVL). Given the available models, Akaike information criterion (AIC) analysis indicated that both skull length and mandible length were the strongest predictors of gape circumference for both external and osteological measurements. Multiple regression analysis of ingestion performance indicated SVL was negatively correlated with the time and number of pterygoid protractions required to consume fish or frogs, indicating that juveniles do not have a higher ingestion performance than adults. While exaggerated morphology in juvenile snakes does not appear to improve ingestion performance, a larger gape should increase the ability of juvenile snakes to consume a wide range of encountered prey shapes and sizes.