Comparative post-weaning ontogeny of the mandible in fossorial and semi-aquatic water voles

Abstract

Comparison of post-weaning ontogenetic changes in bone structures between phylogenetically close species with different ecology and types of locomotion can provide a broader picture of the role that function can play in growth patterns. Since the skulls of water voles of genus Arvicola exhibit an important morphological variation associated with underground or semi-aquatic habitats, we compare postnatal ontogenetic changes in the mandible of A. sapidus (semi-aquatic) and A. scherman (fossorial). A total of 15 two-dimensional landmarks were digitized on 271 mandibles from collection specimens for geometric morphometric analyses. We compared allometric and phenotypic trajectories, ontogenetic form changes, and estimated bite force between these two taxa. Results revealed that in young individuals of both species, important shape changes occur in the angular and condylar processes. Conversely, the mandible shows significant interspecific differences in size and shape, the orientation of allometric and phenotypic trajectories, and estimated bite force. Across the post-weaning ontogeny, with respect to A. sapidus, A. scherman shows an increased diastema, a lower ramus, a ventral and caudal expansion of the condylar process, and a dorsal expansion of the angular process. Likewise, a comparatively higher estimated bite force was found in A. scherman. All these differences seem to be concomitant with the mechanical stress and functional constraints associated with persistent excavation activity in fossorial water voles.