Biased parasitoid sex ratios: Wolbachia, functional traits, local and landscape effects

Adult sex ratio (ASR) is a key demographic parameter, being essential for the survival and dynamics of populations. Biased ASRs are adaptations to the environment on different scales, resulting from different mechanisms such as inbreeding, mating behaviour, resource limitations, endosymbionts such as Wolbachia, and changes in density or spatial distribution. Parasitoid ASRs are known to be strongly biased, but little information is available on how they are affected by large-scale variables such as landscape composition or fragmentation. We examined whether landscape scale variables affect the ASR of several parasitoid species belonging to the same tritrophic gall inducer community. We examined the effects of various explanatory variables on parasitoid ASR: the ovipositor length (a species level functional trait), resource amount (gall size) and density (local scale) as well as habitat amount, land use and landscape history (landscape scale). We controlled for the incidence and prevalence of Wolbachia infections. We found that parasitoid ASR is best explained by and positively correlated with ovipositor length and gall diameter. The interaction of functional traits with habitat availability also significantly explained parasitoid ASRs. Our results support the hypothesis that large-scale environmental characteristics affect parasitoid ASRs in addition to intrinsic and local characteristics.