Sexual dimorphism, bite force and diet in the diamondback terrapin

Abstract

AbstractSexual dimorphism in head size and shape has been documented in many animals and is often thought to be related to the consumption of different prey in males and females thus reducing competition between the two sexes. However, for this to be true, the difference in head size and shape should be associated with a difference in performance allowing one sex to exploit different prey resources. In many durophagous turtle species, females are bigger than males and have bigger heads for a given size. Here, we test whether the observed dimorphism in head size and shape in the durophagous Malaclemys terrapin is reflected in differences in bite force. Furthermore, we measure the forces needed to crush different prey items in order to evaluate whether the observed bite force dimorphism allows access to different dietary resources in females. Finally, we compare head size and shape and bite force between the durophagous M. terrapin and a generalist (Trachemys scripta). Our results show that females of M. terrapin have higher bite forces than males in line with their bigger heads relative to their body size. Moreover, the higher bite forces in females allow them to eat larger as well as different types of snails resulting in differences in diet. Finally, our results show that both sexes of M. terrapin have bigger heads and bite forces for their body size compared to the generalist T. scripta, even as juveniles. Moreover, M. terrapin bite harder even when taking into account differences in head size, suggesting intrinsic differences in the jaw musculature in durophagous species.