Meeting Abstract

P3-129   -   North American river otter exhibits variable limb morphology between two disparate geographic regions Lynch, LM*; Lee, AH; Valdez, DR; Vera Covarrubias, B; Midwestern University, Glendale; Midwestern University, Glendale; Midwestern University, Glendale; Midwestern University, Glendale llynch@midwestern.edu

The transition to an aquatic lifestyle introduces novel environmental selective pressures, which frequently results in limb bone shape and microstructure modifications, such as more robust, curved limbs and increased cortical bone thickness. Semi-aquatic taxa must adapt to the constraints placed by both terrestrial and aquatic modes of locomotion, resulting in limb morphologies that can exhibit traits seen in both environments. While this pattern has been described interspecifically, little is understood about how regional environmental variation affects bone morphology intraspecifically. Using the North American river otter ( Lontra canadensis) as a model, we describe differences in limb bone shape and microanatomy in populations from geographic regions with considerable differences in climate and biome. We measured six limb elements from 19 individuals collected from Alaska and Florida. We quantified bone shape using 3D geometric morphometrics and bone microstructure through linear and volumetric measurements. Via PERMANOVA, we found significant (p<0.05) differences in the shape of the humerus, radius, femur and tibia, with individuals from Alaska having larger articular surfaces and more robust, curved elements. PCA revealed that 85-90% of the variation in bone length, total bone volume, bone cross-sectional robusticity, and total body length relate to an individual’s size. Florida specimens significantly differentiated from Alaska specimens along PC1, with Alaskan specimens having proportionally longer and more robust bones. Our results suggest that regional variation, likely associated with environment, does influence the shape and microstructure of limb elements in this semiaquatic taxon. Future research will provide insight into the selective pressures influencing limb evolution in animals occupying this unique niche.