Sexual dimorphism in epicuticular compounds despite similar sexual selection in sex role‐reversed seed beetles

Abstract

Sexual selection imposed by mating preferences is often implicated in the evolution of both sexual dimorphism and divergence between species in signalling traits. Epicuticular compounds (ECs) are important signalling traits in insects and show extensive variability among and within taxa. Here, we investigate whether variation in the multivariate EC profiles of two sex role-reversed beetle species, Megabruchidius dorsalis and Megabruchidius tonkineus, predicts mate attractiveness and mating success in males and females. The two species had highly distinct EC profiles and both showed significant sexual dimorphism in ECs. Age and mating status in both species were also distinguishable by EC profile. Males and females of both species showed significant association between their EC profile and attractiveness, measured both as latency to mating and as success in mate-choice trials. Remarkably, the major multivariate vector describing attractiveness was correlated in both species, both sexes, and in both choice and no-choice experiments such that increased attractiveness was in all cases associated with a similar multivariate modification of EC composition. Furthermore, in both sexes this vector of attractiveness was associated with more male-like EC profiles, as well as those characterizing younger and nonvirgin individuals, which might reflect a general preference for individuals of high condition in both sexes. Despite significant sexual selection on EC composition, however, we found no support for the proposition that sexual selection is responsible for divergence in ECs between these species.

Epicuticular Compounds of Protopiophila litigata (Diptera: Piophilidae): Identification and Sexual Selection Across Two Years in the Wild

“…Such quantitative sexual dimorphism in EC abundances is prevalent in insects (e.g. Bartelt et al 1986, Jallon and David 1987, Curtis et al 2013, Booksmythe et al 2017.…”

“…ECs play an important role in desiccation resistance by waterproofing the cuticle with a waxy coating (Beament 1945, Wigglesworth 1945), but in multiple species ECs also function as pheromones used as a means of chemical communication. ECs have variously been implicated in species recognition (Martin et al 2008, Dyer et al 2014, kin recognition (Lihoreau and Rivault 2009), group recognition (Fang et al 2002, Vásquez et al 2009, and mate choice , Steiger et al 2013, Booksmythe et al 2017 in diverse insect taxa. Extensive work characterizing ECs in several species of Drosophila has determined that they are plastic in response to aspects of the physical (Stinziano et al 2015) and social environment (Petfield et al 2005, Gershman et al 2014, Gershman and Rundle 2017, and can evolve rapidly in response to altered natural and sexual selection (Blows 2002, Kwan and Rundle 2009, Sharma et al 2012.…”