LAST-MALE SPERM PRECEDENCE BREAKS DOWN WHEN FEMALES MATE WITH 3 MALES

Females of many species commonly mate with several males, yet our know ledge of sperm precedence patterns is based almost exclusively on labo ratory experiments in which females were mated to only two males. In b oth birds and insects, these investigations have generally shown stron g mating order effects, usually with the second male to mate siring mo st of the offspring. In the harlequin beetle-riding pseudoscorpion, si ngle-locus minisatellite DNA profiling has recently revealed extensive multiple paternity within the broods of field-inseminated females. He re, we report the findings of a sperm precedence experiment in which w e investigated this unusual absence of mating order effects. By allowi ng females to mate with only two males, we were able experimentally to induce the pattern of strong last-male sperm precedence typical of ot her two-male mating studies. By contrast, females mated to three males produced broods exhibiting the same highly mixed paternity detected i n this species in nature. The elimination of mating order constraints on sperm utilization when females mate with several males suggests tha t the opportunity for post-copulatory sexual selection may be much gre ater in nature than is evident from two-male mating experiments.