Meeting Abstract

37.1  Wednesday, Jan. 5  Not just a chastity belt: the role of copulatory plugs in Red-sided garter snakes revisited FRIESEN, Chris/R*; MASON, Robert.T; Oregon State University friesenc@science.oregonstate.edu

In promiscuous mating systems, postcopulatory selection and sexual conflict drive male investment in ejaculates. Copulatory plugs (CP) are a gelatinous mass deposited by the male during copulation that can represent a significant proportion of the ejaculate. Passive mate-guarding is the principle function attributed to the CP because it occludes the opening of the female’s reproductive tract and prevents intromission by subsequent males. The CP may also prevent a female from expelling sperm from an “undesirable” male after coerced copulation or when precopulatory choice is otherwise limited. During the spring emergence of Red-sided garter snakes (Thamnophis sirtalis parietalis) in Manitoba, Canada, the operational sex ratio is strongly skewed toward males who scramble to locate and court newly emerged females. Litters usually exhibit multiple paternity suggesting that the females are promiscuous; males deposit copulatory plugs suggesting passive mate-guarding is a wise investment. However, precopulatory female choice is limited in the largest mating aggregations, thus sexual conflict may place a premium on preventing females from ejecting male sperm. In snakes, sperm are produced in the testes and delivered through the ductus deferens, and the copulatory plug is thought to be produced by the renal sexual segment and conveyed through the ureter. We manipulated the delivery of the two fluids separately by ligating the ducts. We found that the CP is not formed in ureter-ligated males and that sperm leaks out immediately after copulation. Further, the CP is analogous to a spermatophore as the protein matrix contains most of the sperm which are liberated over time as the plug dissolves within the female’s vagina.