Polyandry increases offspring fecundity in the bulb mite

The common occurrence of polyandry continues to puzzle evolutionary biologi sts, as female reproductive success is thought to be limited mostly by her fecundity. Here we test whether females of the bulb mite, a species in whic h the females are highly promiscuous, benefit from polyandry in terms of in creased fitness of their progeny. Females were given opportunity to mate wi th either one or six males, but the experiment was designed to allow the sa me number of matings per female in both groups, that is, irrespective of th e number of males. We found that daughters of females mated to six males ha d significantly higher fecundity than daughters of females mated to one mal e, whereas other fitness components of progeny (male virility and longevity of both sexes) were not affected. These findings appear to support hypothe ses proposing that multi-male mating enables females to exercise postcopula tory mate-choice (direct or indirect, via sperm competition) and thus accru e genetic benefits.