MICHIELS, N. K.; BRAUER, B.; University of Muenster, Germany; University of Groningen, Netherlands: The transition from hermaphroditism to dioecy: is sexual conflict important?

Hermaphroditism can outcompete gonochorism when mating opportunities are unpredictable and rare, resulting in diminishing returns for the male function. But what happens to hermaphrodites with frequent mating chances? Empirical data from frequently mating, internally fertilising hermaphrodites suggest that such systems often show copulatory mechanisms that are very costly for the sperm-receiver. Here, I ask whether hermaphrodites are inherently prone to escalations of this kind, and whether costly matings make a transition to gonochorism more likely. Analytical and individual-based models reveal four effects. (1) The chance of obtaining male fitness makes hermaphrodites “mate like males”. As a result, mating rates are generally higher in hermaphrodites than in gonochorists under comparable conditions because in the latter females usually limit male mating rates. (2) Higher willingness to mate makes hermaphrodites accept higher mating costs. (3) If higher paternity can be obtained by harming a sperm-receiving partner, hermaphrodites develop higher levels of harm than males do. (4) Increased male harm suppresses mating rates in both hermaphrodites and gonochorists. In hermaphrodites it leads to a female biased sex allocation. As a result, hermaphrodites may still produce more eggs than gonochorists, despite higher losses of resources due to male harm. These results can explain escalated mating mechanisms in various hermaphroditic systems, but also suggest that the effect of male harm on the transition to gonochorism may be weak. I shall present results in which transitions between hermaphrodites and gonochorists are simulated with and without male harm under various mating scenarios.