Inbreeding depression of mating behavior and its reproductive consequences in a freshwater snail

Theoretical work predicts that the magnitude of inbreeding depression is particularly high in traits that are closely related to fitness. Despite the extensive work on inbreeding depression of male and female reproductive performance, relatively little is known on how inbreeding impairs male and female mating behavior. We studied inbreeding depression of male and female mating behavior in the simultaneously hermaphroditic freshwater snail Physa acuta to test 1) whether there is inbreeding depression of mating behavior, 2) whether the potential of mate competition and mate choice has an effect on the strength of inbreeding depression, 3) whether the magnitude of inbreeding depression differs between both sex functions, and 4) how inbreeding depression of mating behavior translates into inbreeding depression of reproductive success. For this, we compared the mating behavior between selfed (inbred) and outcrossed (outbred) focal snails in a series of mating trials, in which we manipulated experimentally the potential of mate competition and mate choice. Our results provide evidence for moderate inbreeding depression of the number of copulatory encounters, the number of copulations, and the total time spent mating in both sex functions. The magnitude of inbreeding depression did not differ between the levels of competition and between both sex functions. Finally, our results suggest that inbreeding depression of mating behavior only explains a small fraction of the observed inbreeding depression of reproductive success. We discuss the implications of these findings with respect to precopulatory sexual selection and sex-specific inbreeding depression.