Between- and within-individual variation in moth sexual signals: causes and consequences

Sexual signals are an important driving force in the origin of new species. However, many species-specific sexual signals are under stabilizing selection, which limits variation, the raw material for evolutionary change. How then is variation maintained under stabilizing selection? By using the model moth species Chloridea virescens and Chloridea subflexa we identified three potential mechanisms by which variation can be maintained. First, we showed that pairs of C. virescens females, comprising of one attractive and one unattractive signaller, can increase the mating rate of both females, whereas mono-phenotypic pairings appear to compete and have a lower mating rate. In this way, unattractive pheromone variants could be mated due to male mistakes, thereby maintaining variation. Furthermore, we found covariation between fitness and pheromone signal and stability in C. subflexa. We quantified “stability” by sampling pheromone of individual females twice within their lifetime. Females with high fitness showed a more stable signal compared to females with a lower fitness. This trade-off provides a second mechanism for generating variation in sexual communication. We also found that most DNA methylation patterns C. virescens were inherited, although some sites were subject to spontaneous de novo DNA methylation across generations. Thus, DNA methylation in C. virescens could potentially also play a role in generating heritable pheromone variation. Together, these three newly identified mechanisms can help explain the existence of the immense variation in chemical communication signals on which selection can act, which may be the starting point of the emergence of novel sexual communication channels.