Gape and bite force in the rodents Onychomys leucogaster and Peromyscus maniculatus: Does jaw‐muscle anatomy predict performance?

Abstract

Compared with the deer mouse, Peromyscus maniculatus, the grasshopper mouse, Onychomys leucogaster, exhibits modifications in its jaw-muscle architecture that promote wide gapes and large bite forces at wide gapes to prey upon large vertebrate prey. In this study, we determine whether jaw-muscle anatomy predicts gape and biting performance in O. leucogaster, and we also assess the influence of gape on bite force in the two species. Although O. leucogaster has an absolutely longer jaw, which facilitates larger gapes, maximum passive gape is similar in both species, averaging approximately 12.5 mm. Thus, when scaled to jaw length, O. leucogaster has a smaller maximum passive gape. These results suggest that predatory behaviors of O. leucogaster may not require remarkably large gapes. On the other hand, both absolute and relative bite forces exerted by O. leucogaster are significantly larger than those of P. maniculatus. The largest bite forces in both species occur at 5.0 mm of gape at the incisors, or 40% of maximum gape. Although bite force in both species decreases at larger gapes, O. leucogaster does maintain a larger percentage of maximum bite force at gapes larger than 40% of maximum passive gape. Therefore, although structural modifications in the masticatory apparatus of O. leucogaster may constrain gape, they may help to maintain bite force at large gapes. These results suggest that increases in gape differentially influence the length-tension properties of the jaw muscles in the two species. Finally, these results highlight the importance of considering the effect of muscle stretch on force production in comparative studies of bite force. As a first approximation, it appears that gapes of 40-50% of maximum gape in rodents optimizes bite force production at the incisors.

Go big or go fish: morphological specializations in carnivorous bats

“…The fact that carnivorous bats also have evolved cranial features associated with high bite force provides additional support for the importance of wide gapes in the feeding ecology of these bats. Future work measuring maximum passive gapes [70], in vivo bite forces and feeding behaviour from carnivorous bats would help to corroborate these findings.…”

Predicting bite force in mammals: two-dimensional versus three-dimensional lever models

“…In vivo bite force is well documented in reptiles (Erickson et al, 2003;Herrel and Holanova, 2008) but has been reported for only a few species of mammals (Aguirre et al, 2002;Dumont et al, 2009;Hylander et al, 1992;Santana and Dumont, 2009;Williams et al, 2009). Therefore, researchers have turned to models to estimate bite forces based on approximations of the structure of the skull and the physiology of the muscles that adduct the jaws.…”

“…Therefore, researchers have turned to models to estimate bite forces based on approximations of the structure of the skull and the physiology of the muscles that adduct the jaws. Bite force estimates are often used in comparative studies, where they are correlated with ecological tasks (Christiansen, 2007;Kiltie, 1982), stress distribution in the skull (Christiansen and Adolfssen, 2005;Thomason, 1991), and morphological variables such as bite point, gape, skull size or muscle mass (Dumont and Herrel, 2003;Williams et al, 2009). …”

Anti‐predator behaviour in a procellariid seabird: Wedge‐tailed shearwaters do not respond to the odour of introduced ship rats

“…On islands, rats are likely to be introduced in an isolated manner, a few individuals at a time, which may result in a population that does not necessarily impact seabirds. Rat density (Igual et al 2006) and factors intrinsic to rats such as physical-limiting factors (Freeman & Lemen 2008;Williams et al 2009;Zarzoso-Lacoste et al 2011), lack of predation skill or social learning (Grant et al 1981;Booth et al 1996) can alter the magnitude of rat impact on seabirds. Therefore, further experiments should be conducted on a variety of procellariid seabirds, prospecting or breeding birds, and within colonies where the impact of rats is quantified, to determine to what extent ecological factors, bird species characteristics (e.g.…”