Female‐biased sex allocation in wild populations of the eriosomatine aphid Prociphilus oriens: local mate competition or transgenerational effects of maternal investment?

Abstract

AbstractSeveral aphid species exhibit female‐biased sex allocation. Local mate competition (LMC) has been postulated to be the evolutionary factor of the female‐biased sex allocation. We estimated individual sex allocation in the eriosomatine aphid Prociphilus oriens and explained the observed pattern of sex allocation based on a hypothesis other than LMC. On the basis of the relationship between maternal body size and brood size, we estimated the cost of producing a female to be 1.85 times the cost of producing a male. The population‐wide allocation to males was 22–24 %. Winged mothers exhibited a large variation in the number of male and female embryos they had, including 23–30 % of winged mothers producing only female embryos. There was polymorphism in the sex‐ratio expression. Thus, the constant male hypothesis assuming LMC was not supported. Winged mothers that produced an all‐female brood contained larger female embryos than did mothers that produced a bisexual brood. Previous studies have indicated that a large sexual female produces a single large egg, which hatches into a first‐instar larva containing a larger amount of gonads. Thus, in eriosomatine aphids, maternal investment in daughters directly affects the potential fecundity of granddaughters, whereas investment in sons does not. We propose a hypothesis that higher fitness returns from maternal investment in daughters than in sons may have primarily led to the evolution of highly female‐biased sex allocation in P. oriens.