Male–female chemical interactions in a facultatively parthenogenetic stick insect

Abstract

Facultative parthenogenesis is a form of reproduction in which females can either lay unfertilised eggs that typically develop into female offspring only or mate and lay fertilised eggs that develop into male and female offspring. Intriguingly, facultative parthenogens often occur in mixed-sex populations where reproduction is mostly sexual and all-female populations where reproduction is asexual. How all-female populations avoid invasion by males remains unknown. Here, we explored the use of pheromones in male–female communication in a facultatively parthenogenetic stick insect, the peppermint stick insect (Megacrania batesii), and compared chemical signals between females descended from sexually versus parthenogenetically reproducing populations. If parthenogenetic females release less attractive pheromones, this could help explain the persistence of all-female populations. We found that M. batesii exhibits slight sexual dimorphism in antenna morphology, and behavioural assays provided little evidence that males could locate females solely by volatile pheromones. However, CHC profiles differed substantially between different types of females. Analysis of CHC components indicated a clear genetic difference between females descended from all-female versus mixed-sex populations, as well as a maternal effect of female parthenogenetic versus sexual development. Together, our results suggest that males might rely more on close-range chemical cues to differentiate females, and chemical communication could play a role in the persistence of all-female populations.