Male‐male combat drives bite force evolution in the absence of mastication

Abstract

Bite force production is often cited as a key influence on the anatomical evolution of the mammal jaw. However, most research focuses on mastication and food processing as the driving force for the evolution of large bite forces in terrestrial mammals. Pinnipeds (seals, sea lions and walruses) have lost the ability to masticate as an adaptation to marine feeding and instead use their jaws for a wide range of other behavior, including prey capture and male‐male combat in certain polygynous species. This study investigates the influence of male fighting on the jaw morphology of a mammal whose postcrania are entirely specialized for swimming. We measured cortical thickness of males and females of two polygynous (n=14) and three monogamous (n=19) species, from a wide taxonomic range. Section modulus of the corpus was calculated using a hollow beam model and bite force estimated by scaling by jaw length. We find that polygynous species that exhibit male combat (harem‐defense polygyny) produce significantly larger theoretical bite forces than females of the same species and males and females of monogamous species, including those with different feeding specializations. This indicates that male‐male combat is the most important influence on bite force evolution in pinnipeds and is a major contributor to variation in mandibular anatomy.Grant Funding Source: n/a