DELAYED OUTCROSSING IN CAENORHABDITIS ELEGANS BY MATING AVOIDANCE BEHAVIOR

The species Caenorhabditis elegans has a mating system of androdioecy, which consists of hermaphrodites and males. The evolutionary pressures on the two sexes are different. C. elegans hermaphrodites make self-sperm during larval development and therefore are self-fertile, whereas the males have to mate with hermaphrodites to reproduce. Behaviors that increase the reproductive success of each sex may evolve to maximize fitness. Prior studies indicate that self-sperm exhausted hermaphrodites are more receptive to mating while a recent study suggests that males have a preference for sperm-depleted hermaphrodites. These observed behaviors are confounded with receptivity of hermaphrodites, male preference, and the effects of age. In this study, I present mating assays that attempt to disentangle the effects of age, receptivity of hermaphrodite, and male preference on mating success. In the mating assays, a higher proportion of sperm-depleted hermaphrodites mate compared to hermaphrodites that have sperm. During their self-fertile period, hermaphrodites actively avoid mating with males by sprinting away, thus, delaying outcrossing by mating avoidance. Hermaphrodites that are paralyzed due to mutations in their genes do not show mating avoidance behavior. Therefore, mating avoidance is an active behavior of hermaphrodites, which requires locomotion. The velocities of older hermaphrodites that are sperm-depleted are significantly higher than velocities of young hermaphrodites that have sperm. Therefore, older hermaphrodites are capable of mating avoidance but do not avoid mating because they are sperm-depleted. I conclude that sperm-status of the hermaphrodite is a strong predictor of mating avoidance behavior. The sperm-sensing pathway of the hermaphrodites mediates the mating avoidance behavior by dynamically changing the behavior of hermaphrodites.