The shrew tamed by Wolff's law: Do functional constraints shape the skull through muscle and bone covariation?

Abstract

Bone is a highly plastic tissue that reflects the many potential sources of variation in shape. Here, we focus on the functional aspects of bone remodeling. We choose the skull for our analyses because it is a highly integrated system that plays a fundamental role in feeding and is thus, likely under strong natural selection. Its principal mechanical components are the bones and muscles that jointly produce bite force and jaw motion. Understanding the covariations among these three components is of interest to understand the processes driving the evolution of the feeding apparatus. In this study, we quantitatively and qualitatively compare interactions between these three components in shrews from populations known to differ in shape and bite force. Bite force was measured in the field using a force transducer and skull shape was quantified using surface geometric morphometric approaches based on µCT-scans of the skulls of same individuals. The masseter, temporalis, pterygoideus, and digastricus muscles of these individuals were dissected and their cross sectional areas determined. Our results show strong correlations between bite force and muscle cross sectional areas as well as between bite force and skull shape. Moreover, bite force explains an important amount of skull shape variation. We conclude that interactions between bone shape and muscle characteristics can produce different morpho-functional patterns that may differ between populations and may provide a suitable target for selection to act upon.

Does diet drive the evolution of head shape and bite force in chameleons of the genus Bradypodion?

“…Three‐dimensional geometric morphometric approaches using sliding landmarks may be better suited to capture subtle shape variation (Cornette et al . ; Cornette, Tresset & Herrel ) and may potentially change our interpretation of these patterns.…”

“…Possibly, our shape quantification did not accurately capture the variation in the coronoid and the lateral side of the mandible, known to be important insertion sites for the jaw adductors (Fabre et al 2014a,b). Three-dimensional geometric morphometric approaches using sliding landmarks may be better suited to capture subtle shape variation (Cornette et al 2013;Cornette, Tresset & Herrel 2015) and may potentially change our interpretation of these patterns.…”

Do functional demands associated with locomotor habitat, diet, and activity pattern drive skull shape evolution in musteloid carnivorans?

“…The shape of the skull is complex and cannot be adequately represented using a traditional landmark‐based approach (Cornette et al ., , ). Consequently, a 3D sliding semilandmark procedure (Bookstein, ; Gunz, Mitteroecker & Bookstein, ) was used to better quantify the morphology of the skull, and especially the orbits and cranial base (occipital, the foramen magnum, and the occipital condyle).…”

“…These studies have shown that mastication and the associated muscles have a direct effect on cranial shape (Cox, 2008;Herrel et al, 2008;Fabre et al, 2014a). The skull and jaws are crucial in the context of prey capture, prey killing, and the subsequent prey processing and mastication (Anderson, McBrayer & Herrel, 2008;Cornette et al, 2015). To perform these behaviours the muscles that connect the skull to the mandible are activated in order to allow the opening and closing of the mouth as well to generate the forces that reduce the food Fabre et al, 2014a;Cornette et al, 2015).…”

“…The skull and jaws are crucial in the context of prey capture, prey killing, and the subsequent prey processing and mastication (Anderson, McBrayer & Herrel, 2008;Cornette et al, 2015). To perform these behaviours the muscles that connect the skull to the mandible are activated in order to allow the opening and closing of the mouth as well to generate the forces that reduce the food Fabre et al, 2014a;Cornette et al, 2015). In our study, the mean shapes associated with each dietary group show differences in the snout, the dental row length, the braincase morphology, the sagittal crest/temporal line, and in the shape of the zygomatic arch.…”