Morphological and mechanical determinants of bite force in bats: do muscles matter?

Abstract

SUMMARYBats are one of the most diverse groups of mammals and have radiated into a wide variety of trophic niches. Accordingly, the cranial structure in bats is unusually variable among mammals and thought to reflect specializations for feeding and echolocation. However, recent analyses of cranial structure, feeding behavior and bite force across a wide range of bats suggest that correlations between morphology and performance and/or ecology are not as clearcut as previously thought. For example, most of the variation in bite force across a wide range of phyllostomid bats was explained by differences in body size rather than specific cranial traits. However, remarkably little is known about the muscular components that are responsible for generating the actual bite forces. We have tested which aspects of the cranial muscular system are good predictors of bite force across a wide range of species using a modeling approach. Model calculations of bite force show good correspondence with in vivo data suggesting that they can be used to estimate performance of the cranial system. Moreover, our data show that bite force is strikingly well explained by differences in temporalis muscle mass, temporalis fiber length and masseter muscle mass. Moreover, our data show that evolutionary changes in bite force capacity in bats are associated with evolutionary changes in relative m. temporalis mass and absolute skull length.

Morphological innovation, diversification and invasion of a new adaptive zone

“…Thus the range of dietary niches available to stenodermatine bats is effectively broader than that of other phyllostomids. We have not demonstrated that increased bite force is associated with increased fitness in bats, but this is within the realm of possibility, as exposure to tougher foods has been identified as the agent of selection for Diversification and a new adaptive zone E. R. Dumont et al 1803 higher bite forces in a population of lizards [66]. There is only a single instance of convergent evolution of a morphological innovation linked to dedicated frugivory in bats (species in the family Pteropodidae), and that system has not been investigated in sufficient detail to draw close parallels.…”

Go big or go fish: morphological specializations in carnivorous bats

“…Third, a larger size directly results in higher bite force owing to absolutely greater jaw adductor physiological cross-sectional areas (e.g. [30,[54][55][56][57]). These higher bite forces would facilitate prey processing, as prey hardness scales positively with size [58] and carnivorous bats are osteophagous [23,24,26].…”

Ontogenetic changes in jaw-muscle architecture facilitate durophagy in the turtleSternotherus minor

“…Empirically derived muscle stress values for chelonian cranial muscles are not available and 25Ncm -2 is commonly used by investigators attempting to determine theoretical whole muscleforce generation in vertebrates (e.g. Cleuren et al, 1995;Herrel et al, 1999;Herrel et al, 2008). Other verified muscle-stress values (20 and 30Ncm -2 ) were tested in an earlier study (Pfaller, 2009).…”

“…Other verified muscle-stress values (20 and 30Ncm -2 ) were tested in an earlier study (Pfaller, 2009). Bite-force generation was then estimated by developing a static equilibrium model of the forces generated by the jaw adductor muscles and the lever mechanics of the feeding system (Cleuren et al, 1995;Herrel et al, 2008;Huber et al, 2005;Huber et al, 2008). Photographs taken laterally and dorsally during muscle dissections were used to develop three-dimensional coordinate systems for each individual.…”