The ontogenetic scaling of bite force and head size in loggerhead sea turtles (Caretta caretta): implications for durophagy in neritic, benthic habitats

Abstract

Summary Ontogenetic studies of vertebrate feeding performance can help address questions relevant to foraging ecology. Feeding morphology and performance can either limit access to food resources or open up new trophic niches in both aquatic and terrestrial systems. Loggerhead sea turtles are long-lived vertebrates with complex life histories that are marked by an ontogenetic shift from an oceanic habitat to a coastal neritic habitat, and a transition from soft oceanic prey to hard, benthic prey. Although considered durophagous and strong biters, bite performance has not been measured in loggerheads, nor has the ontogeny of bite performance been characterized. In the present study, we collected measurements of bite force in loggerhead turtles from hatchlings to adults. When subadults reach the body size when the ontogenetic shift occurs, their crushing capability is great enough to consume numerous species of hard benthic prey but at smaller sizes. As loggerheads mature and bite performance increases, larger and harder benthic prey become accessible. Loggerhead bite performance eventually surpasses the crushing capability of other durophagous carnivores, thereby potentially reducing competition for hard benthic prey. The increasing bite performance and accompanying morphology of the head and jaws is likely an effective mechanism for resource partitioning and decreasing trophic competition. Simultaneous measurements of body and head size and the use of non-linear reduced major axis regression show that bite force increases with significant positive allometry relative to body size (straight carapace length, straight carapace width, and mass) and head size (head width, height, and length). Simple correlation showed that all logged morphometrics were good predictors of logged bite performance, but an AICc-based weighted regression showed that body size (SCW followed by SCL and mass, respectively) were more likely predictors of bite force than head size morphometrics (HW and HL).