December 2024
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Evolutionary Ecology
Despite their individual reproductive flexibility, populations of many facultatively parthenogenetic animals vary in sex ratio and reproductive mode. Sex-specific dispersal could contribute to such spatial variation. We asked if sex-specific dispersal by adults or nymphs occurs in the facultatively parthenogenetic phasmid Megacrania batesii, which forms a geographical mosaic of mixed-sex (mostly sexually reproducing) and all-female (parthenogenetic) populations. If sex-specific dispersal contributes to sex-ratio variation in this species, we would expect to observe greater dispersal by females than by males. We carried out a mark-resighting field study over three years to investigate adult dispersal in mixed-sex and all-female populations. To better understand how males affect female behaviour, we also investigated pairing and mate-guarding. In addition, we investigated dispersal by hatchling nymphs in a semi-natural enclosure. Mean nightly movement distances did not differ between unpaired (single) females and males in the mixed-sex population. However, unpaired females moved further in mixed-sex than in all-female populations. Many adult females in the mixed-sex population continually carried guarding males on their dorsum. Pairs often remained together for multiple days, and few females or males were observed pairing with multiple partners. Paired females moved shorter distances than unpaired females, and such females’ movement increased following experimental removal of males. Hatchling nymphs rarely moved between plants. Our findings suggest that guarding males affect females’ movement patterns, but nymph and adult dispersal is unlikely to shape spatial variation in sex ratio in Megacrania batesii.