Sex-dependent effects of Wolbachia on antifungal immunity in Drosophila melanogaster.

Wolbachia can enhance dipteran resistance to fungal infections, yet the effects of this symbiont on antifungal defense mechanisms remain poorly understood. We studied immune parameters in male and female Drosophila melanogaster with (W+) and without (W-) Wolbachia. We assessed the constitutive expression of Toll pathway genes and several components of the melanization cascade, including expression of prophenoloxidase genes, phenoloxidase activity, levels of reactive oxygen species, and concentrations of tyrosine, dopamine, and N-acetyldopamine. In addition, we analyzed the induction of Toll signaling components and Toll-related antimicrobial peptides in males and females of the W+ and W- flies following natural infection with the fungus Beauveria bassiana. We show that increased female survival following infection is associated with a Wolbachia-dependent constitutive shift toward catecholamine-dependent melanization.In males, by contrast, the effect of the symbiont is primarily reflected in stronger infection-induced expression of Toll pathway components, particularly spaetzle, dorsal, and Drosomycin. A common feature in both sexes was constitutively elevated expression of Metchnikowin. Together, these results demonstrate that Wolbachia modifies antifungal immunity in a sex-specific manner and highlight new directions for investigating the molecular mechanisms by which Wolbachia influences immune-signaling cascades.