Benefits of multiple mating in a sexually dimorphic polygynandrous insect

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Mating with multiple partners is common across animal taxa. Males mate multiply because reproductive success positively correlates with mating success. In contrast, multiple mating is expected to increase the direct (material) or indirect (genetic) benefits accrued by females but not necessarily increase their reproductive success. Cases in which female reproductive success increases with mating success could be due to females acquiring material resources that directly increase reproductive output. Because multiple mating likely increases reproductive success more in males than in females, males typically experience greater sexual selection. Consequently, males in harem polygynous species, where a few males can monopolize access to several females in a population, are expected to be under stronger sexual selection than females. We field-test these predictions by using the harem polygynous Wellington tree wētā, Hemideina crassidens. Here, we develop microsatellite markers for H. crassidens and use them to genotype females, their offspring and putative sires to estimate the opportunity for selection as well as quantify natural rates of multiple mating and its effect on male and female reproductive success (number of hatchlings). We found that both sexes mate multiply and that reproductive success increases with mating success in both sexes. Males and females have similar total opportunities for selection, and sexual selection comprises approximately 50% of the total selection operating in males. We found that female oviposition rate increases with mating success, but we found no evidence to support the hypothesis that females derive indirect benefits from polyandry. Our study provides strong evidence that male and female H. crassidens derive significant direct fitness benefits from multiple mating under natural conditions.