Bite force in vertebrates: opportunities and caveats for use of a nonpareil whole-animal performance measure

Abstract

Measurements of whole-organism performance traits have been useful in studies of adaptation and phenotypeenvironment correlations. Bite force capacities may be tightly linked to both the type and magnitude of the ecological challenges of food acquisition, mate acquisition, and antipredation in vertebrates. In the present study, we present technical details on bite meters and on measuring bite forces. The ability to take reliable measurements depends on specific features of the measuring device and on where in the mouth the bite is applied. Using both previously available and original data, we demonstrate several ecologically and evolutionarily relevant features of bite force measurements. First, maximal bite forces are repeatable among individuals across all vertebrates studied to date. Second, in ectotherms such as lizards, maximal bite forces are affected by body temperature and motivational states. Third, bite forces are strongly correlated with head size and shape. Fourth, bite forces correlate with features of prey of vertebrates. Finally, bite forces are linked to male dominance and correlated with social-display structures. Thus, bite force performance measures can be used as 'traits', and thus be used in integrative studies at multiple levels of organismal biology. Accordingly, bite force data will help our understanding of the functions, capacities, and evolution of jaw-cranial musculoskeletal systems. Moreover, a plethora of opportunities exist for the use of bite force measurements, and if methods are carefully applied, several levels of organismal and ecological organization can be integrated to aid our understanding of the ecology and evolution of vertebrate taxa. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 709-720. ADDITIONAL KEYWORDS: diet -male-male combat -sexual dimorphism. INTRODUCTIONMulticellular organisms are the sum of integrated form-function complexes (Bock & von Wahlert, 1965). Comparisons among animals varying in formfunction complexes for their relative abilities to perform ecologically relevant tasks (e.g. evading predators and capturing prey, sensu Huey & Stevenson, 1979) enhance our understanding of the evolution of the enormous morphological diversity of animals (Arnold, 1983;Wainwright, 1991). Locomotor performance traits, for example, have been useful tools for analysing the design, function, and evolution of locomotor systems in vertebrates (Irschick & Garland, 2001). Furthermore, analyses of locomotor performance traits have provided insights into our understanding of evolutionary and functional tradeoffs and their roles in the evolution of phenotypic variation (Vanhooydonck, Van Damme & Aerts, 2001;Van Damme et al., 2002).Similarly, performance measures associated with the vertebrate jaw system provide insights with respect to vertebrate ecology and evolution. The jawcranial musculoskeletal system is a hallmark formfunction complex of vertebrates, used to capture, subdue, and orally process prey, and to obtain mates (Motta & ...

Go big or go fish: morphological specializations in carnivorous bats

“…First, is size evolution associated with ecological divergence of carnivorous species from insectivorous ancestors? For a given skull morphology, bite force and gape scale positively with body size in vertebrates [29][30][31][32], and this performance trait can explain food resource use, including the consumption of mechanically challenging foods [32,33]. Thus, we hypothesize that carnivorous bats experienced selection on body size.…”

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

“…All available data from a broad range of durophagous taxa show that bite forces increase disproportionately relative to changes in head and body dimensions across ontogeny (i.e. positive allometry) (Herrel and Gibb, 2006;Anderson et al, 2008). These results suggest that the scaling of traits related to musculoskeletal biomechanics is most likely to explain the allometric patterns of bite force among durophagous taxa Herrel and O'Reilly, 2006).…”

“…Previous studies have also shown that individuals with higher bite forces require less time to consume certain prey items (Herrel et al, 2001;Verwaijen et al, 2002;Van der Meij and Bout, 2006). This suggests that an additional benefit of developing allometrically greater bite forces is that durophagous taxa can increase the net rate of energy intake when foraging (optimal foraging) (MacArthur and Pianka, 1966), and presumably enhance their fitness (Anderson et al, 2008). Because the implications for growth patterns that facilitate high bite-force generation are apparent (Kolmann and Huber, 2009), the feeding systems of durophagous taxa are well suited for investigations of the scaling relationships between musculoskeletal growth, feeding performance and dietary ontogeny.…”

“…Firstly, it can be afforded through increased body size as greater muscle volume confers absolutely greater force generation (Schmidt-Nielson, 1984;Anderson et al, 2008). Secondly, ontogenetic increases in the jawclosing musculature (invariably associated with increased head dimensions), without changes in muscle physiology, lever mechanics or body size, will also lead to absolute increases in bite force.…”

Modeling observed animal performance using the Weibull distribution

“…These studies typically assume accurate measurements of performance, which can be difficult to obtain, sometimes with a few observations contributing to a final point estimate of performance, especially when maximum performance values are of interest (Anderson et al, 2008;Garland and Losos, 1994). For the initial approval of projects by animal use and collection review boards, it is also necessary to plan for the number of individuals to be tested, the testing procedure for each individual and the resulting statistical power of the results.…”