Polyandry increases male offspring production in the quasi-gregarious egg parasitoid Anaphes nitens

Abstract

In this work we explored the female mating frequency of the quasi-gregarious egg parasitoid Anaphes nitens and its consequences on offspring sex-ratio. In a previous study we have shown that sex-ratio (proportion of males) increases with maternal age, suggesting that sperm depletion could occur if females mate only once. Here, we tested: (1) whether A. nitens females are polyandrous; (2) whether polyandry increases daughter production; and (3) the relationship between polyandry, fecundity and longevity. Virgin females were mated and provided with host egg-capsules and drops of honey as food. Afterward, they had the opportunity to re-mate daily during the rest of their life. About 55% of females were polyandrous, but multiple mating significantly increased the proportion of males in the offspring. In particular, daughter production of multi-mated females crashed at the 9th day of life, despite having obtained 2–3 matings. Hence, this suggests that females did not replenish their spermatheca by additional mating additional and that the amount of sperm received in a single copulation could be enough to produce an unconstrained offspring sex allocation. It is possible that the observed sex-ratio could depend on a limited storage capacity of the spermatheca or on the onset of physiological problems such as difficulty of sperm transfer, sperm plugs or displacement. Up to 52% of the multi-mated females did not produce any progeny after the first copulation. This suggests that a second mating was useful to obtain viable sperm. Furthermore, polyandry did not affect fecundity or longevity. Polyandry may be adopted to prevent matings with sperm depleted or incompatible males or to reduce the male harassment frequently experienced under laboratory conditions.