Clade-wide variation in bite-force performance is determined primarily by size, not ecology

Abstract

Performance traits are tightly linked to the fitness of organisms. However, because studies of variation in performance traits generally focus on just one or several closely related species, we are unable to draw broader conclusions about how and why these traits vary across clades. One important performance trait related to many aspects of an animal’s life history is bite-force. Here, we use a clade-wide phylogenetic comparative approach to investigate relationships between size, head dimensions and bite-force among lizards and tuatara (lepidosaurs), using the largest bite-force dataset collated to date for any taxonomic group. We test four predictions: that bite-force will be greater in larger species, and for a given body size, bite-force will be greatest in species with acrodont tooth attachment, herbivorous diets, and non-burrowing habits. We show that bite-force is strongly related to body and head size across lepidosaurs and, as predicted, larger species have the greatest bite-forces. Contrary to our other predictions, tooth attachment, diet and habit have little predictive power when accounting for size. Herbivores bite more forcefully simply because they are larger. Our results also highlight priorities for future sampling to further enhance our understanding of broader evolutionary patterns.

Inter‐relationships among body mass, body dimensions, jaw musculature and bite force in reptiles

“…Positive relationships among measures of body size and bite force have been shown several times previously for within species (e.g. Herrel et al., 2006) and among species (Erickson et al., 2012; Isip et al., 2022; Jenkins & Shaw, 2020). Although explored for birds (Deeming et al., 2022), this study is the first to demonstrate the relationships for body size with total jaw muscle mass, which ultimately generates bite force, are unaffected by order of reptile.…”

“…(2002) for turtles and Isip et al. (2022) for lizards. Using data from lizards, Jenkins and Shaw (2020) illustrated strong linear relationships between snout–vent length and bite force, and between head depth and bite force but did not report allometric exponents.…”

“…However, Isip et al. (2022) have recently demonstrated that in lepidosaurs bite force is better explained as a function of both body length and head size rather than other ecological factors.…”

“…Data for bite force, mainly derived from in vivo studies, are well reported for a wide range of lizards and crocodilians, although less so for testudines and snakes. Inter‐specific comparisons among body dimensions and bite force are limited to a few reports for crocodilians (Erickson et al., 2012), testudines (Herrel et al., 2002) and lizards (Isip et al., 2022; Jenkins & Shaw, 2020). The only study into the interspecific relationship between bite force and the mass of the jaw musculature is for bird species (Deeming et al., 2022).…”

“…There is a positive relationship between snout-vent length and bite force in Lepidosauria, which also relates to diet (e.g. Herrel et al, 2014;Jenkins & Shaw, 2020), but see Isip et al (2022). However, there are other associations with bite force in reptiles, which include association with sexual selection inter alia: sexual dimorphism, for example in the lizard Sauromalus ater in which males bite other in territorial disputes (Lappin et al, 2006), or mating success, for example in the lizard Crotaphytus collaris (Lappin & Husak, 2005).…”