Meeting Abstract
Sexual dimorphism attributed to niche divergence is often linked to differentiation between the sexes in both dietary resources and traits related to feeding and resource use. Recent studies have indicated that southern sea otters (Enhydra lutris nereis) exhibit intersexual differences in the degree of dietary specialization as well as in craniomandibular size and shape. Whether these differences translate to differences in functional traits between the sexes remains to be investigated. To test the hypothesis that scaling patterns of bite force, a metric of feeding performance, exhibit intersexual differences, we calculated theoretical bite forces of 55 naturally deceased southern sea otters spanning the size ranges encountered over ontogeny. We then used standardized major axis regressions to simultaneously examine the scaling patterns of theoretical bite forces and morphological components across ontogeny and assess whether these scaling patterns differed between the sexes. We found that positive allometric increases in theoretical bite force resulted from positive allometric increases in physiological cross-sectional area for the major jaw adductor muscle and in mechanical advantage. In our analysis of sexual dimorphism, we found that scaling patterns of theoretical bite force and morphological traits do not differ between the sexes over ontogeny. However, adult male sea otters exhibited greater absolute bite forces as a result of their larger sizes rather than differences in scaling patterns in any particular trait. Our results provide some support for the niche divergence hypothesis throughout late adulthood. Future work may link intersexual differences in feeding functional morphology with foraging ecology to further validate the role of niche divergence in the maintenance of sexual dimorphism in sea otters.
