Résumé
Inbreeding depression has become a central theme in evolutionary biology
and is considered to be a driving force for the evolution of reproductive
morphology, physiology, behavior, and mating systems. Despite the
overwhelming body of empirical work on the reproductive consequences of
inbreeding, relatively little is known on whether inbreeding depresses
male and female fitness to the same extent. However, sex-specific
inbreeding depression has been argued to affect the evolution of selfing
rates in simultaneous hermaphrodites and provides a powerful approach to
test whether selection is stronger in males than in females, which is
predicted to be the consequence of sexual selection. We tested for
sex-specific inbreeding depression in the simultaneously hermaphroditic
freshwater snail Physa acuta by comparing the reproductive performance of
both sex functions between selfed and outcrossed focal individuals under
different levels of male–male competition. We found that inbreeding
impaired both male and female reproductive success and that the magnitude
of male inbreeding depression exceeded female inbreeding depression when
the opportunity for sperm competition was highest. Our study provides the
first evidence for sex-specific inbreeding depression in a hermaphroditic
animal and highlights the importance of considering the level of male–male
competition when assessing sex differences in inbreeding depression.