The Male Sex Pheromone of the Butterfly Bicyclus anynana: Towards an Evolutionary Analysis

Abstract

BackgroundFemale sex pheromones attracting mating partners over long distances are a major determinant of reproductive isolation and speciation in Lepidoptera. Males can also produce sex pheromones but their study, particularly in butterflies, has received little attention. A detailed comparison of sex pheromones in male butterflies with those of female moths would reveal patterns of conservation versus novelty in the associated behaviours, biosynthetic pathways, compounds, scent-releasing structures and receiving systems. Here we assess whether the African butterfly Bicyclus anynana, for which genetic, genomic, phylogenetic, ecological and ethological tools are available, represents a relevant model to contribute to such comparative studies.Methodology/Principal FindingsUsing a multidisciplinary approach, we determined the chemical composition of the male sex pheromone (MSP) in the African butterfly B. anynana, and demonstrated its behavioural activity. First, we identified three compounds forming the presumptive MSP, namely (Z)-9-tetradecenol (Z9-14:OH), hexadecanal (16:Ald ) and 6,10,14-trimethylpentadecan-2-ol (6,10,14-trime-15-2-ol), and produced by the male secondary sexual structures, the androconia. Second, we described the male courtship sequence and found that males with artificially reduced amounts of MSP have a reduced mating success in semi-field conditions. Finally, we could restore the mating success of these males by perfuming them with the synthetic MSP.Conclusions/SignificanceThis study provides one of the first integrative analyses of a MSP in butterflies. The toolkit it has developed will enable the investigation of the type of information about male quality that is conveyed by the MSP in intraspecific communication. Interestingly, the chemical structure of B. anynana MSP is similar to some sex pheromones of female moths making a direct comparison of pheromone biosynthesis between male butterflies and female moths relevant to future research. Such a comparison will in turn contribute to understanding the evolution of sex pheromone production and reception in butterflies.

Biased learning affects mate choice in a butterfly

“…Alternatively, premating social experience could alter signal weighting. B. anynana, like many animals, uses both olfactory and visual signals to assess mate quality (16,17,34,35). Sex pheromone production is variable in male B. anynana and changes with age (35,36).…”

Selection on male sex pheromone composition contributes to butterfly reproductive isolation

“…We first removed any peak smaller than 10 ng, to homogenize the detectability of compounds between samples and to permit the identification of all selected peaks. Despite the ability of GC-EAD to detect the presence of olfactory receptors for chemicals present in minute amounts, the B. anynana MSP was shown to be formed by the most abundant, male-specific and repeatable compounds [25]. We thus selected the compounds on average more than five times more abundant in males than in females and present in at least two out of three sampled males.…”

“…Furthermore, it has been demonstrated that male sex pheromone (MSP) plays a key role in mate choice in the model species Bicyclus anynana [25][26][27]. After landing behind a female, B. anynana males flicker their wings and erect their androconial hair, probably favouring the dissemination of MSP at short range [25]. Therefore, we postulated that selection on differentiation in the sex pheromone composition has produced recurrent RCD in this butterfly genus.…”

“…Interestingly, the key taxonomic trait used to distinguish Bicyclus species is the number and position of androconia [24], the wing structures thought to be involved in the production and emission of male sex pheromone. Furthermore, it has been demonstrated that male sex pheromone (MSP) plays a key role in mate choice in the model species Bicyclus anynana [25][26][27]. After landing behind a female, B. anynana males flicker their wings and erect their androconial hair, probably favouring the dissemination of MSP at short range [25].…”

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

“…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.…”