Last-male sperm precedence breaks down when females mate with three males

Abstract

Females of many species commonly mate with several males, yet our knowledge of sperm precedence patterns is based almost exclusively on laboratory experiments in which females were mated to only two males. In both birds and insects, these investigations have generally shown strong mating order effects, usually with the second male to mate siring most of the offspring. In the harlequin beetle-riding pseudoscorpion, single-locus minisatellite DNA profiling has recently revealed extensive multiple paternity within the broods of field-inseminated females. Here, we report the findings of a sperm precedence experiment in which we investigated this unusual absence of mating order effects. By allowing females to mate with only two males, we were able experimentally to induce the pattern of strong last-male sperm precedence typical of other two-male mating studies. By contrast, females mated to three males produced broods exhibiting the same highly mixed paternity detected in this species in nature. The elimination of mating order constraints on sperm utilization when females mate with several males suggests that the opportunity for post-copulatory sexual selection may be much greater in nature than is evident from two-male mating experiments.