Reliable quantification of bite-force performance requires use of appropriate biting substrate and standardization of bite out-lever

Abstract

Bite-force performance is an ecologically important measure of whole-organism performance that shapes dietary breadth and feeding strategies and, in some taxa, determines reproductive success. It also is a metric that is crucial to testing and evaluating biomechanical models. We reviewed nearly 100 published studies of a range of taxa that incorporate direct in vivo measurements of bite force. Problematically, methods of data collection and processing vary considerably among studies. In particular, there is little consensus on the appropriate substrate to use on the biting surface of force transducers. In addition, the bite out-lever, defined as the distance from the fulcrum (i.e. jaw joint) to the position along the jawline at which the jaws engage the transducer, is rarely taken into account. We examined the effect of bite substrate and bite out-lever on biteforce estimates in a diverse sample of lizards. Results indicate that both variables have a significant impact on the accuracy of measurements. Maximum bite force is significantly greater using leather as the biting substrate compared with a metal substrate. Lessforceful bites on metal are likely due to inhibitory feedback from mechanoreceptors that prevent damage to the feeding apparatus. Standardization of bite out-lever affected which trial produced maximum performance for a given individual. Indeed, maximum bite force is usually underestimated without standardization because it is expected to be greatest at the minimum out-lever (i.e. back of the jaws), which in studies is rarely targeted with success. We assert that future studies should use a pliable substrate, such as leather, and use appropriate standardization for bite out-lever.

Reproductive phenotype predicts adult bite‐force performance in sex‐reversed dragons (Pogona vitticeps)

“…The bite plates of the smaller transducer were shallower and more closely opposed so that the smallest animals did not have to use excessive gape angles, which might restrict maximum performance (Figure 1). Strips of leather (about 5 mm wide) were added to the outer tips of the bite plates to protect the animal's jaws and teeth, to provide a naturalistic surface to bite, and to ensure that the bite force being applied was at a consistent point along the bite plates (Figure 1; Lappin & Jones, 2014). The output voltage of the devices was calibrated to bite force (Newtons) by hanging a series of weights by a string positioned at the center of the leather strip (cf.…”

“… Note : ZZf, sex‐reversed females ( n = 17), ZWf, concordant females ( n = 11), ZZm, males ( n = 11). Mass, body mass (g); SVL, snout‐vent length (mm); HLrr, head length directly from the tip of the rostrum to the posterior end of the retroarticular process (mm); HLrq, head length from the tip of the rostrum to the posteroventral corner of the tympanum (approximately the position of the quadrate‐articular jaw joint) (mm); HWqu, head width measured at the base of the tympanum (mm); HWmt, head width measured at the midpoint of the temporal region (mm); HDmt, and head depth measured at the midpoint of the temporal region (mm); BF at tips, bite force at the tips corrected for out lever (N; Lappin and Jones, 2014); BF no lever, bite force without lever correction (N).…”

“…To accommodate the size range of specimens tested, two different sized sets of bite plates were used ( Figure S2) that differed in their width: 25 mm (also used here: Jones & Lappin, 2009;Lappin, Hamilton et al, 2006;Lappin & Husak, 2005;Lappin & Jones, 2014) and 20 mm wide (used here for the first time). The bite plates of the smaller transducer were shallower and more closely opposed so that the smallest animals did not have to use excessive gape angles, which might restrict maximum performance ( plates to protect the animal's jaws and teeth, to provide a naturalistic surface to bite, and to ensure that the bite force being applied was at a consistent point along the bite plates ( Figure 1; Lappin & Jones, 2014). The output voltage of the devices was calibrated to bite force (Newtons) by hanging a series of weights by a string positioned at the center of the leather strip (cf.…”

Evolution of cranial shape in a continental‐scale evolutionary radiation of Australian lizards

“…; Herrel et al. ; Jones , Lappin and Jones ), providing a readily understood adaptive reason for the evolution of this skull shape. However, advantages may not be without costs and in some cases ecological trade‐offs may be operating to optimize function in particular habitats.…”

“…Some skull morphologies have readily understood functional benefits that may explain why the shape has evolved. Short snouts, and broad and deep skulls with large adductor chambers all contribute to greater bite forces (Olson 1961, Herrel et al 1999Herrel et al 2001;Jones 2008, Lappin andJones 2014), providing a readily understood adaptive reason for the evolution of this skull shape. However, advantages may not be without costs and in some cases ecological trade-offs may be operating to optimize function in particular habitats.…”