Current Research

Study Species

Since 1991, the Mason Lab has been studying the biology of the red-sided garter snake (Thamnophis sirtalis parietalis) in the northernmost extent of its range in the Interlake Region of Manitoba, Canada. We have also conducted research on two local species of garter snakes (T. s. concinnus, T. ordinoides) which provide us with a rich comparative context for our numerous research areas. Lastly, we have just begun to incorporate a sympatric species of garter snake (T. radix) that overwinters with T. s. parietalis in Manitoba.

Current Research Areas

1. The role of the Harderian gland in the chemical ecology of garter snakes

   We have recently discovered that the Harderian gland (HG), the largest cephalic gland in garter snakes, plays a critical role in the transfer of chemical signals (female pheromones, feeding cues) to the chemosensory epithelium of the vomeronasal organ (VNO). Male garter snakes who have had their HGs removed fail to court females and exhibit no response to female pheromone. The HG ducts to the VNO and thus bathes the VNO epithelium with secretions. We have strong evidence that these HG secretions contain compounds that play perireceptor roles in the snake chemosensory system by enabling the pheromone to travel to the VNO. Sarah Moore, a Ph.D. student in the lab, is studying these putative binding proteins.

2. Pheromones in garter snakes

   Dr. Robert Mason was the first scientist to isolate, identify, and synthesize a pheromone from a reptile, and his discovery fostered several research areas into the role of pheromones in the reproductive biology of garter snakes. Previous work by Dr. Michael LeMaster examined the intrasexual, seasonal, and population-level variation in the sexual attractiveness pheromone produced by female red-sided garter snakes. He has continued to collaborate with Dr. Mason and has involved several undergraduate students from Western Oregon University in projects that aim to describe species differences in pheromone composition from several garter snake species (e.g. Thamnophis ordinoides, Thamnophis radix). In the Mason lab, Rocky Parker (Ph.D. candidate) has recently shown that temperature plays a critical role in the production of the female sexual attractiveness pheromone, and he is currently working on the she-male garter snakes that produce a female-similar pheromone. Emily Uhrig, another graduate student in the lab, is studying the species-level differences in pheromone composition.

3. Comparative and experimental endocrinology

   The red-sided garter snake shows strong patterns of seasonality, which are reflected in their behavior and circulating levels of sex and stress hormones. This species serves as a model dissociated breeder, meaning that their maximal mating behavior is uncoupled from gametogenesis and maximal sex steroid production. Several previous students in the Mason lab have explored different aspects of the endocrinology of this and sister taxa (T. s. concinnus, T. S. sirtalis). Currently, Rocky Parker (Ph.D. candidate) is using classical endocrinology methods (castration/hormone replacement) to describe the relationship between sex steroid hormones and pheromone production in both sexes of the red-sided garter snake.

4. Evolution of mating systems and strategies

   Our focal species has a polygynandrous mating system that is excellent for investigating sperm competition, cryptic female choice, sperm storage, and sexual conflict, as numerous collaborative projects with Dr. Richard Shine have reported. Female red-sided garter snakes use stored sperm from multiple matings, and thus post-copulatory sexual selection and coevolution are likely important factors in this mating system. Previous collaborative work with Dr. Stevan Arnold and Dr. Suzanne Estes shed light on multiple paternity in this species, and Chris Friesen, a current Ph.D. candidate in the lab, is exploring the consequences of limited female pre-copulatory choice. By looking at patterns of paternity, seasonality of mating, and mating frequency of both males and females, we hope to gain insight into the factors that drive sexual selection (e.g. Bateman's gradients) and sexual conflict in this system and how each sex has responded to resolve conflict.

5. Metabolic cost of courtship and mating

   In our system, the sex ratio is skewed, with males greatly outnumbering females during the spring mating season. Thus, males scramble to gain access to females, leading to mating balls of up to one hundred snakes. During the mating season, the snakes do not eat and engage in very robust, stereotypical courtship behavior that involves significant levels of activity. We have recently started a collaboration with Dr. Don Powers to assess the metabolic cost of courtship for these snakes. Chris Friesen (Ph.D. candidate) is working with Dr. Powers on this topic, and he is using two separate approaches (doubly labeled water and respirometry) to address this question.

If you are interested in becoming a part of the Mason lab, please contact Dr. Mason directly (masonr@science.oregonstate.edu) or one of his grad students for more information (Rocky Parker, parkermi@science.oregonstate.edu or Chris Friesen, friesenc@science.oregonstate.edu).