Skull Size and Biomechanics are Good Estimators of In Vivo Bite Force in Murid Rodents

Abstract

Rodentia is a species-rich group with diversified modes of life and diets. Although rodent skull morphology has been the focus of a voluminous literature, the functional significance of its variations has yet to be explored in live animals. Myomorphous rodents, including murids, have been suggested to represent "high-performance generalists." We measured in vivo bite force in 14 species of wild and lab-reared murid rodents of various sizes and diets to investigate potential morphofunctional differences between them. We dissected their skulls and computed a biomechanical model to estimate bite force. We first tested if our model allowed good estimation of in vivo data. Then, using morphological, in vivo and estimated bite force data in a phylogenetic context, we aimed to find the drivers of bite force differences among species. Estimated and in vivo bite forces were strongly correlated, which indicates that (a) biomechanical models allow a good estimation of real performance, and that (b) size and muscular changes (increased mass, fiber length, and PCSA) are the main drivers of bite performance differences. Myomorphous rodents, therefore, may have evolved high bite force through a combination of changes in size and musculature, which gave them a great versatility in their ability to process food. We found mixed results at the intraspecific level, with only some species displaying a good fit between estimated and in vivo measurements. We suggest that limited variation in size and muscular organization, and increased behavioral variation might decrease the precision of bite force estimates within species. Anat Rec, 301:256-266, 2018. © 2018 Wiley Periodicals, Inc.

Morphometric models for estimating bite force in Mus and Rattus: mandible shape and size do better than lever-arm ratios

“…Of course, even more precise estimations of bite force can be obtained by using PCSA to calculate muscle forces (Ginot et al, 2018). However, the aim of the paper was specifically to test and compare 'simplistic' morphological estimators that are currently used by the community, rather than try to obtain the most precise estimation possible.…”

“…combining muscle physiological cross-sectional area (PCSA) and lines of action] or mechanical descriptors (combinations of mandibular measurements) in these studies allowed the accurate estimation of bite force (compared with in vivo data) at the interspecific level. However, Ginot et al (2018) showed that these estimates of bite force were less precise at the intraspecific level. Furthermore, this approach requires the accurate dissection of muscles, to dissolve them and measure fiber length for individual muscle strands, and is therefore time consuming and inapplicable to specimens for which muscles have not been preserved.…”

“…The influence of skull and mandible morphology on in vivo bite force performance has also been directly tested, using various anatomical variables (e.g. Freeman and Lemen, 2008;Ginot et al, 2018). The use of biomechanical models [i.e.…”

“…Notably, the strong allometric component of shape variation means that shape also integrates a large part of the signal linked to size. Although it is expected that more complex methods, using muscular characteristics to estimate forces, will give much better estimations (see Ginot et al, 2018), the aim of this paper was to verify and compare the validity of osteological proxies that are easy to access (allowing large sample sizes), already in use in the literature and available even when soft tissues are absent (e.g. paleontology).…”

Behavioral Correlates of Cranial Muscle Functional Morphology

“…The next paper in the issue (Ginot et al, 2018), submitted by Samuel Ginot and an excellent team of coauthors, meshes an impressive dataset of in vivo bite forces and anatomical data from 75 animals spanning 14 rodent species. Although one of us (Santana) collected similar data on bats, the other (Hartstone-Rose) is jealous of the ability to study bite forces and anatomy in the same individuals across such a wide sample-something seldom if ever possible for many lineages of mammals.…”