Effects of repeated mating and polyandry on the fecundity, fertility and maternal behaviour of female earwigs, Euborellia plebeja

I examined multiple mating and its function in female earwigs, Euborellia plebeja (Dermaptera: Anisolabididae). Like other earwigs, females of this species care for their eggs and intermittently lay eggs in clutches (iteroparity). Analysis of two polymorphic allozyme loci revealed that wild-caught adult females laid clutches with low within-brood genetic relatedness (0.210), indicating that females were promiscuous under natural conditions. Rearing experiments in the laboratory revealed that: (1) repeated mating with a single male increased female fecundity (number of clutches laid) and hence the number of hatchlings produced; (2) estimated sperm number was positively correlated with hatchability; (3) when frequency of mating was controlled, polyandry enhanced hatchability, although this effect was not statistically significant; (4) duration of maternal care varied for clutches with low hatchability, and sometimes exceeded the mean interclutch interval. Thus, although a possible benefit of polyandry is suggested, the greater beneficial effect of repeated mating on female fecundity can explain polyandrous mating in this species. Because female earwigs invest considerable effort in brooding their clutches, it may be adaptive to suppress oviposition unless stored sperm ensures high fertility.