Profiles of cuticular hydrocarbons mediate male mate choice and sexual isolation between hybridising Chrysochus (Coleoptera: Chrysomelidae)

Abstract

Chemical signals frequently underlie sexual isolation between insect species. Our understanding of the evolutionary forces influencing these signaling systems is known for very few systems, challenging both our efforts to understand insect speciation, and our ability to predict longterm changes in the chemical communication systems of insects. Thus, we are in need of more systems in which both the chemical signals causing sexual isolation and the evolutionary forces driving sexual isolation are understood. Sexual isolation in the hybrid zone between Chrysochus cobaltinus and C. auratus has apparently increased in response to natural selection against hybridisation (i.e. reinforcement). Previous experiments suggested that this isolation was due, at least in part, to male preferences for conspecific females. Here, we confirm this role of male choice, and document that male mate choice in this system is influenced by cuticular hydrocarbon (CHC) profiles. Specifically, male C. cobaltinus responses to control cadavers and conspecific female cadavers painted with different cuticular hexane extracts, together with analyses of the composition of those extracts, revealed that male mate choice is governed by CHC profiles. Multivariate analyses of GC profiles demonstrated that those profiles are indeed both sex-and species-specific. Although GC-MS enabled identification and quantification of the specific cuticular hydrocarbons, we have not yet determined which individual compounds govern mate choice. Having established that CHCs influence sexual isolation in this system, we can now assess the evolutionary lability of these cues, which will inform both our understanding of speciation, and of the conditions under which the chemical signaling systems that influence mate choice in insects can evolve.

Adaptation to different host plant ages facilitates insect divergence without a host shift

“…We used transformed data to conduct a canonical discriminant analysis with leaving-one-out crossvalidation. A multivariate ANOVA was performed to test whether leaf chemistry differs between elm age classes, sites and the interaction between them [50,51].…”

Composition of cuticular lipids in the pteromalid wasp Lariophagus distinguendus is host dependent

“…While social insects also use CHCs for recognition and interaction with nestmates and as fertility and dominance signals (Singer, 1998;Liebig, 2010), solitary insects mainly use CHCs for the discrimination of conspecifics and enemies, location of mating partners and the elicitation of courtship behaviour (Ruther et al, 2011). Evidence for solitary insects using CHCs as contact sex pheromones comes from several insect orders, for example the Coleoptera (Buprestidae: Lelito et al, 2009;Silk et al, 2009;Cerambycidae: Ginzel, 2010; Chrysomelidae: Sugeno et al, 2006;Peterson et al, 2007;Geiselhardt et al, 2009), Diptera (Drosophilidae, Glossinidae and Muscidae: Wicker- Thomas, 2007;Ferveur & Cobb, 2010) and Hymenoptera (Syvertsen et al, 1995;Schiestl et al, 2000;Sullivan, 2002;Mant et al, 2005;Steiner et al, 2005Steiner et al, , 2006Steiner et al, , 2007. Within the parasitic wasp family Pteromalidae, females of Roptrocerus xylophagorum (Sullivan, 2002), Lariophagus distinguendus (Steiner et al, 2005(Steiner et al, , 2007, Nasonia vitripennis (Steiner et al, 2006) and Dibrachys cavus (Ruther et al, 2011) produce CHCs which act at short-range as contact sex pheromones eliciting courtship behaviour in males.…”

Genetics of cuticular hydrocarbon differences between males of the parasitoid wasps Nasonia giraulti and Nasonia vitripennis

“…Although difficult to demonstrate, several studies provide evidence for CHCs being involved in prezygotic reproductive isolation (for example, Coyne et al, 1994;Peterson et al, 2007). However, what evolutionary forces cause the divergence of CHCs between populations and how many genes with what functions are involved during this process is still largely unknown.…”