Morphological correlates of bite force and diet in the skull and mandible of phyllostomid bats

P>Bite force is an important performance measure for vertebrate and is related to a variety of ecological challenges. Phyllostomid bats present highly diversified feeding habits associated with extensive cranial shape divergence. Biomechanical models predict that the cranial shape changes are linked to dietary variation through bite force. However, the relationship of cranial shape, diet and bite force had not been explicitly tested before. Here we use a combination of geometric morphometric techniques and comparative methods to test for morphological correlates of bite force and diet in 14 phyllostomid bat species. Skull and mandible shape variation were assessed by vectors, derived from a two-block partial least squares analysis of geometric shape and size-independent bite forces. The relationship between bite force, skull shape and diet was assessed by phylogenetic generalized least square regressions. Most variation in the bite force data examined here (approximately 74%) was explained by size variation alone, but the shape vectors for both skull and mandible explained a significant part of the residual variation in bite force (83% and 56%, respectively), as did the dietary differences (56%). Although the first principal component of diet variation is associated with a negative correlation between insectivory and frugivory, residual bite force and cranial shape are not associated with this diet contrast. Shape and residual bite force variation in the sample were strongly associated with the second diet component, depicting an increase in nectarivory. Species with stronger bites (insectivorous and frugivorous) than expected for their sizes presented a shorter rostrum and mandible, higher skulls, and more developed muscle attachment areas. On the other hand, the characteristic cranial elongation of nectarivorous species (supporting the long tongue) is a trade-off with bite force. These morphological correlates of bite force are similar to those observed in carnivores and non-herbivorous marsupials, and can be related to morphological characters used in biomechanical models for bite force prediction. Our results reinforce the effectiveness of statistically integrating geometric shape variables to bite force and diet information in the investigation of patterns of cranial shape change and trophic radiation in ecologically diverse vertebrate groups.