Recently mated males of a lek-mating insect intensify precopulatory mate guarding under male competition

Precopulatory mate guarding is often observed when the availability of female gametes is limited. However, in the lek-mating lesser wax moth, Achroia grisella, this behaviour would result from a constraint on the release of male ejaculate. After a recent mating, males can quickly take hold of, and thereby monopolize, a female until they are able to transfer a new spermatophore. In the present study, we investigated how perceived male competition and female mass affected precopulatory mate guarding as well as eupyrene sperm allocation in this species. In our first experiment, both males and females of a pair were exposed to the playback of either a courtship song (competitive environment) or a silent environment (control) prior to and during the second mating of the male with a virgin female of varying body mass. To disentangle male versus female contributions to the observed behaviours, we conducted a second experiment where either the male only or the female only was exposed to the playback. In both experiments, pairs involving males exposed to playback showed shorter mating latencies and longer copulation durations than control pairs, while the sum of both durations was statistically indistinguishable between groups. Differential mating latencies in both experiments demonstrate a male, not a female, response to perceived male competition. Similar total durations across treatments suggest similar spermatophore production times and the differences in copulation durations probably represent a by-product of differential mating latencies. We found no difference in the number or proportion of sperm transferred during second copulations between treatments or according to female size. Together, these results suggest that plastic precopulatory mate guarding may be adaptive, as it allows males to maximize their reproductive success by securing mates under intense male competition and simultaneous sperm depletion, a combination particularly prevalent in lek mating systems.