Dispersal and foraging rates of the facultatively parthenogenetic stick insect Megacrania batesii

Abstract

Sexual conflict could play an important role in shaping spatial variation in sex ratio in facultatively parthenogenetic species. This is because if females of such species avoid mating, they can establish all-female populations via parthenogenetic reproduction. By contrast, if females cannot avoid mating (i.e., males), they reproduce offspring of both sexes and establish mixed-sex populations in the wild. In Australia, natural populations of Megacrania batesii exhibit extreme spatial variation in sex ratio, with all-female and mixed-sex populations occurring over a small scale. However, it is unclear how facultatively parthenogenetic females avoid mating and establish all-female populations. Sex-specific patterns of dispersal could play a role because, depending on whether females are mated or unmated, they could establish mixed-sex and all-female populations if they successfully disperse to new areas. However, if males invade all-female populations, they could convert these populations into mixed-sex populations via mating. In chapter one, I therefore investigated dispersal rate of females and males from a mixed-sex population and single females from an all-female population. I found that females from the all-female population were less dispersive than females and males from the mixed-sex population. I also found that dispersal was limited to movement within habitat patches. Additionally, in chapter two, I examined whether costs associated with mate guarding (which is widespread and long-lasting in M. batesii) imposes energetic costs on females (i.e., reduction in foraging rate) because guarded females carry males. If females’ foraging rates were impacted by guarding males, mate guarding could be a manifestation of sexual conflict in M. batesii. However, I found little evidence that laboratory-reared females from mixed-sex populations fed more while unpaired than while paired with males. Overall, these studies contribute insights into how sex-specific dispersal and costs of mating and guarding might contribute to sexual conflict and variation in sex ratio in natural populations of the facultative parthenogenetic species, M. batesii.