Food stress causes sex-specific maternal effects in mites

Life history theory predicts that females should produce few large eggs under food stress and many small eggs at abundant food. We tested this prediction in three female-biased size dimorphic predatory mites feeding on herbivorous spider mite prey: Phytoseiulus persimilis, a specialized spider mite predator; Neoseiulus californicus, a generalist preferring spider mites; Amblyseius andersoni, a broad diet generalist. Irrespective of predator species and offspring sex, most females laid only one small egg under severe food stress. Irrespective of predator species, the number of female but not male eggs decreased with increasing maternal food stress. This sex-specific effect was likely due to the higher production costs of large female than small male eggs. The complexity of response to varying spider mite prey availabilities correlated with the predators' degree of adaptation to this prey. Most A. andersoni females did not oviposit under severe food stress, whereas N. californicus and P. persimilis did oviposit. Under moderate food stress, only P. persimilis increased its investment per offspring, at the expense of egg number, and produced few large female eggs. At abundant prey, P. persimilis decreased the female egg sizes at the expense of increased egg numbers resulting in a sex-specific egg size/number tradeoff. Maternal effects manifested only in N. californicus and P. persimilis. Small egg size correlated with the body size of daughters but not sons. Overall, our study provides a key example for sex-specific maternal effects, i.e. food stress during egg production more strongly affected the large than small offspring sex.