Résumé
Sex allocation theory predicts that simultaneous hermaphrodites evolve to
an evolutionary stable resource allocation, whereby any increase in
investment to male reproduction leads to a disproportionate cost on female
reproduction and vice-versa. However, empirical evidence for sexual
trade-offs in hermaphroditic animals is still limited. Here, we tested how
male and female reproductive traits evolved under conditions of reduced
selection on either male or female reproduction for 40 generations in a
hermaphroditic snail. This selection favors a reinvestment of resources
from the sex function under relaxed selection towards the other function.
We found no such evolutionary response. Instead, juvenile survival and
male reproductive success significantly decreased in lines where selection
on the male function (i. e., sexual selection) was relaxed, while relaxing
selection on the female function had no effect. Our results suggest that
most polymorphisms under selection in these lines were not
sex-antagonistic. Rather, they were deleterious mutations affecting
juvenile survival (thus reducing both male and female fitness) with strong
pleiotropic effects on male success in a sexual selection context. These
mutations accumulated when sexual selection was relaxed, which supports
the idea that sexual selection in hermaphrodites contributes to purge the
mutation load from the genome as in separate-sex organisms.