Selection on male sex pheromone composition contributes to butterfly reproductive isolation

Abstract

Selection can facilitate diversification by inducing character displacement in mate choice traits that reduce the probability of maladaptive mating between lineages. Although reproductive character displacement (RCD) has been demonstrated in two-taxa case studies, the frequency of this process in nature is still debated. Moreover, studies have focused primarily on visual and acoustic traits, despite the fact that chemical communication is probably the most common means of species recognition. Here, we showed in a large, mostly sympatric, butterfly genus, a strong pattern of recurrent RCD for predicted male sex pheromone composition, but not for visual mate choice traits. Our results suggest that RCD is not anecdotal, and that selection for divergence in male sex pheromone composition contributed to reproductive isolation within the Bicyclus genus. We propose that selection may target olfactory mate choice traits as a more common sensory modality to ensure reproductive isolation among diverging lineages than previously envisaged.

Covariation and phenotypic integration in chemical communication displays: biosynthetic constraints and eco‐evolutionary implications

“…In contrast to the importance of individual compounds in plant communication, information conveyance in animals (insects) often requires multiple compounds in specific ratios (Löfstedt, ; Symonds & Elgar, ; Bacquet et al ., ). For instance, recognition cues or sex pheromones in hymenopterans, where cuticular hydrocarbons have specific ratios, are used to discriminate between friends and foes (in nest mate recognition cues) or to identify mating partners (Kühbandner et al ., ; Leonhardt et al ., ).…”

“…The modularity and integration found in CCDs have implications for the evolution of chemical communication. It has been discussed that the progress of ecological speciation, which often involves changes in CCDs in both plants and animals (Schiestl & Johnson, ; Bacquet et al ., ), is determined by the number of genetically (or in the context of this study biosynthetically) independent traits with no covariation (Nosil & Harmon, ). Modularity of CCDs reduces the number of independent traits and the number of modules may determine the effective number of selectable units.…”

Expanded molecular phylogeny of the genusBicyclus(Lepidoptera: Nymphalidae) shows the importance of increased sampling for detecting semi-cryptic species and highlights potentials for future studies

“…The male sex pheromones differ between B. dorothea and B. jefferyi (Bacquet et al, 2015), but we unfortunately have no such data for B. moyses. Preliminary studies of male genitalia fail to find any discernible differences.…”

“…Androconia were often overlooked in early taxonomic work on Bicyclus, but as species numbers increased and identification became more challenging they gradually gained importance in species descriptions. More recently the pheromonal functions of Bicyclus androconia (Nieberding et al, 2008) and their links to speciation process (Bacquet et al, 2015) have been the focus of new research.…”

Revision of the Bicyclus ignobilis species-group (Lepidoptera: Nymphalidae: Satyrinae) with descriptions of two new species

“…The holotype and some Nigerian paratypes were caught in 2009 during fieldwork for a study of sex pheromones in Bicyclus (Bacquet, Brattström et al 2015). Due to the way sampling for this project was carried out they have had their wings removed from the thorax and one side of the wings has been dissected and used for pheromone analyses.…”