Disentangling precopulatory and postcopulatory sexual selection in polyandrous species

Sexual selection operates on a sequence of events, from mating to offspring production. Which stages in this sequence undergo stronger selection, especially the relative importance of pre- versus postcopulatory processes, are intensely debated issues. Unequal siring success among mates of polyandrous females is classically taken as evidence for a large contribution of postcopulatory processes to the variance in male reproductive success (var(RSm)). However paternity skews also depend on the timing and number of copulations, a source of variation that should be considered precopulatory rather than postcopulatory. We develop a method for decomposing var(RSm) accounting for copulatory activity and apply it to experimental mating groups of the snail Physa acuta. In our experiment, 40% of var(RSm) emerges at the precopulatory stage, only half of which depends on variation in mating success (number of partners). Ignoring copulation characteristics can therefore lead to severe underestimation ...