Investigating the ecomorphology and evolution of sexual dimorphism in mammalian skulls

University Of Washington, Seattle WA

Investigators

Abstract

Mammals display remarkable variation in the form and function of their skulls, related to what and how they eat. However, the skulls of individuals within a species can vary. If we ignore these differences, we risk missing important clues about how animals behave and adapt to their environments. This project will investigate which carnivoran mammals (i.e., bears, cats, dogs, and their relatives) show differences between males and females and why. The researchers will measure traits such as size and shape, biting ability, bone structure, and bone strength of skulls using computer models based on 3D scans of samples from local and national museum collections. The researchers will then test for differences in skull form between the sexes and whether they translate to differences in skull function. Finally, the researchers will test whether differences can be explained by diet or other aspects of their biology. The project will produce large datasets of 3D skull models. These will be saved in an online database that experts, educators, and the public alike can use to explore and learn. The project will also support training of undergraduate students and outreach and educational programs at a museum that reaches thousands of visitors a year. Understanding how ecological variation influences phenotypic diversification is a central goal of evolutionary biology. However, variation in ecology and phenotypes is not always uniform among different species, and the functional implications of morphological dimorphism remain largely unknown despite well documentation of this phenomenon (i.e., morphological dimorphism) in many mammals. In this project, the researchers will investigate the underlying evolutionary processes of sexual dimorphism and its influence on the evolution and ecomorphological diversification of the carnivoran skull. The researchers will use micro-Computed Tomography, lever mechanical modeling, and finite element analyses to quantify the degree of sexual dimorphism in the size, shape, and functional traits of the skull and test if these sexually dimorphic morphologies translate to intersexual differences in the structural mechanics, performances, and biomechanics of the skull. The researchers will then use phylogenetic comparative methods to (1) determine how sexual selection, niche divergence, and other evolutionary processes influence the evolution of these sexual dimorphic traits; (2) test how sexual dimorphism influences skull ecomorphological diversity and its tempo and mode of evolution; and (3) investigate how sex-specific static allometry contributes to the evolutionary allometry of sexual dimorphism. Overall, this work will demonstrate how intraspecific variation within the sexes affects the adaptive diversification of phenotypic traits, contrary to most other macroevolutionary studies that typically examine only one sex or species means. This work will also identify the multiple underlying processes that influence and facilitate the evolution of sexual dimorphism, thus moving the focus from sexual selection to other potential ecological factors. Lastly, the researchers will also develop a Course-based Undergraduate Research (CURE) program to train and mentor undergraduate students in research and partner with a large natural history museum to disseminate results to public audiences through outreach events. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.