Meeting Abstract

P2-161    Variation in ecomorphology between co-occurring pine squirrels Poorboy, DM*; Calede, J; Chavez, AS; The Ohio State University; The Ohio State University at Marion; The Ohio State University poorboy.1@buckeyemail.osu.edu

An organism’s bite force can be a limiting factor in feeding, mating, and defense such that maximal bite force, a component of feeding efficiency and dietary accessibility, correlates with competitive ability and lifetime fitness. In the North Cascades region of Washington state, two sciurid species: Douglas squirrels (Tamiasciurus douglasii ) and red squirrels (Tamiasciurus hudonicus ), are sympatric and hybridize in a narrow secondary contact zone of subalpine forest near the crest of the Cascade Range. Furthermore, the respective species ranges on opposing sides of the hybrid zone coincide with drastic differences in the hardness of available food items. This system represents an ideal natural laboratory to examine differences in dietary ecomorphological traits in allopatry and sympatry, as well as to explore the phenotypes of hybrid individuals. We investigated whether dietary ecomorphology differs between populations of each individual species in different habitats, whether the two species differ from each other in sympatry, and the phenotypes of hybrids. To test this, we used museum specimens to estimate bite force from an incisor strength-based index, measured the complexity of major cranial sutures, and performed geometric morphometrics of the mandible and cranium. We found that while the two species do differ from each other in dietary ecomorphology, populations of the respective species in different habitat do not differ. For the measured traits hybrids did not differ from either respective species, with mean trait values being an intermediate between those of parental species with greater variation than is observed within either species. These results suggest that dietary ecomorphological traits of these closely evolved species have diverged under selection in their respective parental ranges and are relatively non-plastic.