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

Abstract

Summary Small body size imposes limitations on the feeding capabilities of juveniles, particularly 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 if juveniles have better feeding performance relative to adults. Investigations of snake feeding ontogeny have not found support for the compensation hypothesis. I tested this hypothesis 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 measures and maximum gape circumference showed negative allometry compared to snout-vent length (SVL). Given the available models, 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 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.