Résumé
Sexual selection is a potent evolutionary force that has been shown to
vary in strength and direction depending on demographic factors such as
density and sex ratio. However, the effect of other environmental factors
on the mode of sexual selection remains largely unexplored. Here, we
tested experimentally how food restriction affects the potential for
sexual selection in the male and the female sex function of the
simultaneously hermaphroditic freshwater snail Physa acuta. We manipulated
food availability and compared Bateman’s metrics of sexual selection
between groups of five well-fed and five food-restricted snails.
Food-restricted individuals had a reduced female reproductive output,
suggesting that we successfully manipulated the reproductive resources.
Importantly, food restriction reduced the male opportunity for sexual
selection (in terms of a lowered variance in male mating success) and led
to diminishing returns of mating in both sexes (in terms of nonsignificant
Bateman gradients). Furthermore, we observed significant changes in the
relative contribution of different fitness components, suggesting stronger
postcopulatory selection in the male sex role and stronger fecundity
selection in the female sex role under restricted food conditions. This
study highlights the need to incorporate ecological factors to better
understand how sexual selection operates in the wild.