RESEARCH

Research Focus

skulls

My general research interests examine the links among form, function, evolutionary selection and life history. My research explores how the responses to functional pressures (such as locomotion and reproduction) differ between males and females. I ask questions that are evolutionarily relevant to mammals as a whole and highlight a relatively ignored aspect of female biomechanical evolution.

The pelvis serves three biomechanical roles in mammals: weight-bearing, parturition (giving birth) and locomotion. For this reason, much of my research focuses on this structure. Weight-bearing effects pelvic shape due to the stress that body mass places on the rear limbs. Parturition affects pelvic shape by requiring an ample aperture for the passage of offspring. Finally, locomotion affects pelvic shape through requirements for limb orientation and muscle attachment, with pelvic shape varying considerably as locomotor mode varies, even within the same species.

Using geometric morphometric techniques, as well as comparative phylogenetic analyses, I examined the tie in between form, function and evolutionary history. Examining the shape of an orgamism in the context of their evolutionary history can tell a great deal about the selective pressures that lead to their present form.

Adaptations of the Skeletal System to Increased Activity

bones

In collaboration with Dr. Theodore Garland at UC Riverside, this research examines the morphology of multiple structures (pelvis, scapula, and semicircular canals of the inner ear) critical in the performance and control of locomotion. We are examining morphological changes across generations of mice originating from an outbred strain of Mus musculus (the house mouse) currently used in a long-standing artificial selection experiment. By examining individuals selected exclusively for high locomotor activity, we can examine how such selection drives morphological adaptation, and subsequently, how these adaptations interact with changes in other morphological structures, and locomotor performance.



3D reconstructions of mouse semicircular canals using high resolution CT scans. Work done in collaboration with Benedikt Halgrimsson and Heather Jamniczky at the University of Calgary http://homepages.ucalgary.ca/~morpho/ .

Sexual Dimorphism in Pelvic Structure

This research has taken two directions. First is my research based on museum specimens to examine limb and pelvic shape across a broad group of mammals. This research has focused specifically on carnivores, a group that exhibits a large degreee variation in body size (the least weasel weighs 4.2 g and the polar bear weighs 475 000 g), a wide array of locomotor modes from highly aquatic (e.g., pinnipeds) to semi-fossorial (e.g., badgers), to cursorial (e.g., cheetahs) and variation in sexual size dimorphism. This broad sampling allows me to test the hypothesis that certain locomotor modes produce greater constraints on partuitive capacity than others, but that this effect is moderated by other factors such as relative offspring size.

A second facet of this work involves direct experimental manipulation. Building on the work done in collaboration with the Hayes lab at the University of Nevada, Reno to examine the ties between partuitive events (giving birth) and the associated changes in skeletal morphology of the pelvis in females, I am now  examining how selection for high voluntary wheel running, which reduced body mass, but not offspring mass or litter size affects pelvic morphology, dimorphism and potentially, offspring survival.

Mus sexual dimorphism





Morphological Patterns in Channel Island Foxes

fox skull

I examined differential cranial and pelvic dimorphism two Urocyon (gray fox) species. These species provide an interesting case of the functional effects of mammalian dwarfism often found in island systems (Schutz, et al. 2009a Biological Journal of the Linnean Society.96:339-353). We found that although the Channel Islands fox is 25% smaller than its mainland counterpart in terms of body size, it gives birth to relatively larger offspring and has an increased magnitude of pelvic dimorphism. This runs counter to the allometric patterns seen in body size dimorphism of vertebrates and implies that the rapid evolutionary body size changes experienced by island mammals may have reproductive consequences in terms of pelvic morphology.