The diverse Hawaiian Drosophila and their gut microbes – the role of bacteria and fungi in fly phenotype

A well-functioning gut microbiome provides a number of benefits for many organisms that include enhanced immune defense, digestion, detoxification, and reproduction. The role of bacterial communities in host physiological functions is well-documented. However, much less is known about the contributions of fungi and their interactions with bacteria even though fungi are significant components of many microbiomes, including those of humans and insects. Here, we used antibacterial and antifungal drugs to manipulate the gut microbiome of a Hawaiian picture-wing Drosophila species, D. grimshawi, and identified distinct, sex-specific roles for the bacterial and fungal components of the microbiome in reproduction and lipid composition. Whilst fly lifespan was not affected by any of the antimicrobial treatments, female mating, egg laying, and fecundity were significantly diminished when fungal communities were suppressed. By contrast, male fecundity was more strongly affected by bacterial but not fungal populations. For males and females, suppression of both bacteria and fungi almost completely eliminated fecundity, implicating the importance of interkingdom interactions on reproduction. Overall, our results reveal the importance of interkingdom dynamics in maintaining microbiome community stability and facilitating reproductive function and uncover the differential use of microbes by males and females. Considering the rapid diversification of Hawaiian flies across the archipelago, distinct microbial communities may facilitate species diversification.