Meeting Abstract
Reproductive activities and immune functions are energetically costly and frequently exhibit tradeoffs. When a pathogen is encountered, immune activity may increase at the expense of reproduction, or reproductive investment may be maintained at the expense of immunity. As the endocrine system influences both reproduction and immunity, tradeoffs are often hormonally-mediated. While immune-reproductive tradeoffs have been widely studied in taxa with associated breeding patterns, few studies have investigated such tradeoffs in dissociated breeders where gametogenesis and peak sex steroid hormone levels occur outside the breeding season. In the current study, we investigated immune-reproductive tradeoffs in a dissociated breeder with well-studied reproductive behaviors and physiology: the red-sided garter snake (Thamnophis sirtalis parietalis). During the breeding season, we injected male snakes with lipopolysaccharide (LPS) or saline. LPS, a bacterial endotoxin, elicits an immune response, but is non-pathogenic. Following treatment, we conducted mating trials and collected blood samples for hormone analyses. Our results indicate that LPS-treated males substantially reduce reproductive investment as indicated by decreased courtship and mating success. LPS-treated males that mated produced smaller copulatory plugs than control males, but sperm counts where unaffected by treatment. The immune-reproductive tradeoff appears to be hormonally-mediated as LPS-treated males had elevated corticosterone and depressed androgen levels. Our results show that dissociated breeders are not free from tradeoffs, although the nature of the tradeoff may be influenced by their breeding pattern.
