The troublesome gift: The spermatophylax as a purveyor of sexual conflict and coercion in crickets

Abstract Nuptial food gifts are an integral feature of the mating systems of a wide variety of insects. A pervasive feature of the majority of these gifts is that they afford the male direct access to the female's physiology. Although in some cases such gifts may represent a form of nutritional investment in females, an alternative hypothesis posits that nuptial food gifts may allow males to manipulate female physiology in favor of male interests. This hypothesis predicts that the chemical composition of nuptial food gifts should be driven by a sexual conflict over offspring paternity. We evaluate this hypothesis by reviewing our accumulated studies on decorated crickets, Gryllodes sigillatus , a species that has illuminated key elements of this evolutionary arms race. Here, nuptial food gifts take the form of a spermatophylax, a gelatinous mass forming part of the male's spermatophore and consumed by the female after mating. We first review the evidence for the two principal sexual conflicts arising from the provision of the spermatophylax: (i) a sexual conflict over female acceptance of gifts, and (ii) a conflict over female remating that appears to be mediated by refractory-inducing substances contained in gifts. We then consider the mechanisms by which these conflicts are mediated, focusing specifically on: (i) multivariate selection analyses of the free amino acid composition of the spermatophylax; (ii) proteomic studies identifying candidate proteins that alter female behavior; and (iii) comparative transcriptomic studies showing how gene expression is altered through nuptial feeding.