1. Estimating ingestible size from native mammal prey species Kayla McNeilly Faculty Mentors: Dr. Matthew Close and Dr. Karen Powers, Biology Department, Radford University, Radford, VA 24142 Introduction Preliminary Results Future Research & Discussion Methods Literature Cited Acknowledgments Printing Supported by the RU Office of Undergraduate Research and Scholarship Snakes are gape-limited predators that swallow their prey whole, and therefore the ingestibility of a prey item is determined by its cross-sectional area. Previous studies of body size in laboratory rodents (Muridae) showed that the “ingestible” size of prey is often smaller that what might be predicted from standard measures of body size alone, and better estimates of ingestible size can be generated by manually reducing prey cross-sectional area (CSA; Close and Cundall, 2012). Understanding how minimal CSA relates to predator-prey relationships in the field requires the understanding of ingestible size in native species. In order to answer the question of how standard measures of body size in native species relates to their ingestible size, we collected measurements of mass, head and body length, total length, hind foot, and minimal cross-sectional diameter from rodents native to the New River Valley. We examined 2 adult white-footed mice (Peromyscus leucopus) and 8 meadow voles (Microtus pennsylvanicus) Animal carcasses measured were frozen/thawed as they had previously been salvaged from prior field studies Standard body size measurements (mass, total body length, head and body length, hind foot length) were collected at the time animals were initially collected The cross-sectional area of the thawed animals was determined by rolling rodents tightly in a cylinder and the inner diameter was measured using calipers. CSA of the rolled prey item was then estimated using the formula: A=πr 2. Body size measurements were scaled to cross-sectional area measurements by performing regression of log body size (x) on log cross-sectional area (y). Following measurements, animals were skinned and for taxidermal preparation of skins and skeletons. Whole bodies of prey are not typically recovered in field studies involving analyses of predator stomach contents and/or feces Correlate the size of bone to ingestible size of prey Can help determine what native snakes have been preying on Analyze relationships between standard body size measures and ingestible sizes of additional native rodent species that are common snake prey Analyze relationship between predator head and body size and ingestible prey size in future field studies I would like to thank Dr. Matthew Close and Dr. Karen Powers (Biology Department, Radford University) for letting me use their resources. Specimens acquired from and prepared for the RU Natural History Collection, http://www.radford.edu/content/csat/home/biology/facilities/natural- history-collection.html http://www.radford.edu/content/csat/home/biology/facilities/natural- history-collection.html Close, M., & Cundall, D. 2012. Mammals as Prey: Estimating Ingestible Size. J Morphol. 273, 1042-1049. SlopeY-intR2R2 Mass0.51.90.70 Hindfoot0.112.6 0.002 0 Head & Body 0.630.710.63 Top two panels show Microtus at rest. The bottom image shows rodent rolled up in tube shape (mylar used for display purposes only). The black circles to the right represent corresponding cross sectional areas of rodent under each treatment (resting vs. rolled). Microtus skeleton (top) prepared using dermestid beetles. Scaled images of prey skeletons allow for bone lengths to be measured and correlated to ingestible size measures. Eastern rat snakes (Pantherophis alleghaniensis, bottom left ) and Northern copperheads (Agkistrodon contortrix, bottom right) are native predators of voles. Regression of Microtus Measurements on CSA Prey mass and body length scalesto prey CSA with negative allometry, and both variables underestimates ingestible prey size Prey hindfoot length has little to no relationship to CSA Additional statistical analyses (Reduced Major Axis Regression) will be performed with larger sample to determine the significance of results Photo credit: Dr. Bob Sheehy