Bite force variation in the European pond turtle: Role of morphology, strength, body condition and population of origin

Abstract

Bite force is a biomechanical trait that serves as a valuable proxy for assessing ecological interactions, feeding specialisations, and evolutionary pressures. Chelonians are a unique model system in studies of masticatory performances due to their akinetic skull and lack of teeth. It is known that body size, head morphology and sex-related differences influence bite performance of some chelonian species. In this study, we investigated the variation in bite force within and among five populations of the European pond turtle (Emys orbicularis) in Serbia. We examined relationship of bite force with phenotypic traits such as body size, head dimensions, body condition and muscle strength, as well as body temperature and seasonality. Bite force was measured in the field (N = 209) with an adapted digital force sensor. Our results showed significant differences in bite force across populations, suggesting that local ecological conditions may play a crucial role in shaping bite performance. In particular, turtles from more diverse and structurally complex environments, and turtles sharing their habitat with non-native pond sliders (Trachemys scripta ssp.) exhibited higher bite forces. We also detected a positive association between bite force and maximal pulling force, volumetric body condition index, body size and head height. Surprisingly, sex, cloacal temperature and seasonality were not significant predictors of bite force. Despite the challenges of measuring maximal performance under field conditions, our findings illustrate how variation in functional traits can reflect both intrinsic factors and ecological context, with implications for the study of biomechanical adaptations across animal taxa.