Does ecology shape geographical parthenogenesis? Evidence from the facultatively parthenogenetic stick insectMegacrania batesii

Abstract

Closely related sexual and parthenogenetic species often show distinct distribution patterns, known as geographical parthenogenesis. These patterns, characterized by a mosaic of separate sexual and parthenogenetic populations across their natural range, can also be found in facultative parthenogens – species in which every female is capable of both sexual and parthenogenetic reproduction. The underlying mechanisms driving this phenomenon in nature remain unclear. Features of the habitat, such as differences in host plant phenotypes or niche breadth, could favour sexual or asexual reproductive modes and thus help to explain geographical parthenogenesis in natural insect populations.Megacrania batesiiis a facultatively parthenogenetic stick insect that displays geographical parthenogenesis in the wild. We aimed to explore whether sexual and parthenogenetic populations ofM. batesiidisplayed niche differentiation or variations in niche breadth that could explain the separation of the two population types. To do this, we sampled host plants from across the range ofM. batesiiand quantified phenotypic traits that might affect palatability or accessibility forM. batesii, including leaf thickness, toughness, spike size and density, height, and chemical composition. We also quantified host plant density, which could affectM. batesiidispersal. We found little evidence of phenotypic differences between host plants supporting sexual versus asexualM. batesiipopulations, and no difference in host-plant density or niche breadth between the two population types. Our results suggest that habitat parameters do not play a substantial role in shaping patterns of geographical parthenogenesis in wild populations ofM. batesii. Instead, population sex ratio variation could result from interactions between the sexes or dispersal dynamics.