Very short mountings are enough for sperm transfer in Littorina saxatilis

Conflict over reproduction between females and males exists because of anisogamy and promiscuity. Together they generate differences in fitness optima between the sexes and result in antagonistic coevolution of female and male reproductive traits. Mounting duration is likely to be a compromise between male and female interests whose outcome depends on the intensity of sexual selection. The timing of sperm transfer during mounting is critical. For example, mountings may be interrupted before sperm is transferred as a consequence of female or male choice, or they may be prolonged to function as mate guarding. In the highly promiscuous intertidal snail Littorina saxatilis, mountings vary substantially in duration, from less than a minute to more than an hour, and it has been assumed that mountings of a few minutes do not result in any sperm being transferred. Here, we examined the timing of sperm transfer, a reproductive trait that is likely affected by sexual conflict. We performed time-controlled mounting trials using L. saxatilis males and virgin females, aiming to examine indirectly when the transfer of sperm starts. We observed the relationship between mounting duration and the proportion of developing embryos out of all eggs and embryos in the brood pouch. Developing embryos were observed in similar proportions in all treatments (i.e. 1, 5 and 10 or more minutes at which mountings were artificially interrupted), suggesting that sperm transfer begins rapidly (within 1 min) in L. saxatilis and very short matings do not result in sperm shortage in the females. We discuss how the observed pattern can be influenced by predation risk, population density, and female status and receptivity.