Chris R. Friesen

Ph. D. Candidate, Department of Zoology, Oregon State University
B.S. (Philosophy), Summa Cum Laude, Oregon State University, 2006
B.S. (Zoology) Summa Cum Laude, Oregon State University, 2006

Placing snakes in an arena at the Chatfield Station

3029, Cordley Hall
Oregon State University
Corvallis, Oregon, 97331

Phone: 541-737-5695


Mason Laboratory- Robert T. Mason

Department of Zoology

Home page for Oregon State University

Curriculum Vitae (Teaching Emphasis)


Mating systems are the product of dynamic evolutionary processes. The allocation of parentage determines the effective population size, strength and direction of inter- and intra-sexual sexual selection, and is strongly influenced by energetic, ecological, and historical constraints. At any point in the evolution of a mating system the interests of the sexes may be incongruent and sexual conflict becomes manifest, often to the detriment of females.

With my research I hope to understand how sexual conflict influences female mating strategies by studying both pre- and post-copulatory mechanisms of sexual selection using the red-sided garter snakes of Manitoba, Canada as a model system (Thamnophis sirtalis parietalis).

In Manitoba during spring emergence, mating aggregations of red-sided garter snakes exhibit an operational sex-ratio that is strongly skewed towards males. Males scramble to locate and court females who seem to be coerced into mating within large ‘mating-balls’ at the den (up to 100 males per mating-ball). It is hard to imagine that females within the den have much opportunity for pre-copulatory choice, which would be a form of sexual conflict. Thus, the Manitoba garter snake system is a unique model system in which I can study the evolutionary consequences of sexual conflict on sperm competition and potentially cryptic female choice (CFC).

Working with Suzanne Estes at Portland State University, I have used PCR to assign paternity in litters from multiply-mated females to establish the prevalent patterns and variance in paternity to assess the level and frequency of polyandry. I will use data from these paternity analyses, field observations, courtship trials, and controlled matings to determine when and why females ‘choose’ to mate. Further, I am collaborating with Dave Froman here at Oregon State University to assess within population variation in sperm mobility, a proxy for sperm competitive ability. I am also interested in how the sperm from different males are stored within the female’s reproductive tract in an effort to understand potential mechanisms of CFC or at the very least what determines sperm precedence.

My graduate work here in the Mason Lab began with a study of the metabolic costs of courtship in male red-sided garter snakes using doubly labeled water and respirometry. An extension of that work compliments my work on female choice. In a collaboration with Don Powers from George Fox University, we are using respirometry to test whether females are induced to mate by the physiological stress of courtship. If so, this would support the hypothesis that sexual conflict occurs in this mating system in the form of coercive matings.

Courtship Trials. Chatfield Field Station, Manitoba, Canada

Field Observations. Inwood, Manitoba, Canada.

Female moving through a mass of males with three males aligned with her head.

Male chin-rubbing and tongue flicking to pick up female sex pheromone.

Mass of snakes. Inwood, Manitoba.

Measuring male courtship costs in a metabolic chamber. Chatfield Field Station.