Dietary influences on head and neck ranges of motion in neotropical bats

The primary functions of the tetrapod neck are to maintain head stability and facilitate head mobility. Both stability and mobility should be especially important during foraging. Head stability facilitates the function of the vestibulocochlear, auditory, and visual organs while mobility allows for the motion of that visual field as well as the mouth for food capture and processing. Species that rely on different resources should be under different selective pressures with regard to range of motion of the head and neck and the musculoskeletal morphologies that sustain them. Bats are useful model species to investigate these pressures because they display a wide variety of foraging behaviors. This study tests the hypothesis that dietary regime influences maximum ranges of motion found in the head and neck. To test this hypothesis, a dietarily diverse group of bats were caught in the field and their active ranges of head–neck motion were measured via photographs. Diet information was taken from the literature. Additionally, gross neck dimensions (mediolateral neck width and craniocaudal neck length) were measured using calipers. Phylogenetic statistical methods support the hypothesis and demonstrate that frugivorous species have much smaller ranges of head and neck motion. The results indicate that frugivorous species may require stiffness in their cervical spine in order to carry heavy fruits and maintain head stability simultaneously. Future work should investigate the anatomical differences in the head and neck among bats that influence this stiffness as well as other dietary behaviors that could be shaping the form and function of the head and neck.