The red-sided garter snakes (Thamnophis sirtalis parietalis) of Manitoba, Canada, have been extensively studied for decades with little investigation into their immune system. These animals live very close to the arctic circle and spend over half of the year underground brumating. The annual cycle of the red-sided garter snakes make for an interesting model for investigating the impact of life at extreme latitudes on immune function. Such ecoimmunological investigations have, as of yet, included few ectothermic vertebrates.
Seasonal and sexual variation of the immune response has been found across vertebrate taxa. It is also understood that a trade-off exists between reproduction and the constructive immune response. The research in Chapter 2 of this thesis aims to explore the sexual and seasonal variation of the antimicrobial capabilities of blood plasma as a measure of variation in the innate immune response in red-sided garter snakes. Our results support the hypothesis that the reproduction and immune function trade-off is facultative as antimicrobial capabilities of plasma were greatest during seasons of active foraging and lowest during seasons where foraging was not taking place. The only sexual variation detected was found in reproductive animals; with reproductive animals demonstrating reduced antimicrobial capabilities during some seasons.
In Chapter 3, the antimicrobial capabilities of plasma from naturally injured individuals were compared to healthy individuals. In this study, we found that injured individuals had reduced antimicrobial abilities but neither sex of the animal nor severity of the injury had any correlation with this difference. This study suggests that either prioritization on reproduction or prioritization within the immune system is occurring in injured animals.
The research in this thesis is setting the groundwork for ecoimmunological investigations utilizing the red-sided garter snake as a model. The immense amount of research that has taken place with this population over the past five decades has given us a wealth of information regarding physiological systems and behaviors that are involved with or related to immune function. This makes the red-sided garter snake a compelling model for further ecoimmunological investigations and the work in this thesis provides the foundation necessary for these further investigations.