Microbiome-mediated resilience and cross-generational consequences in male Drosophila exposed to combined environmental stressors

Climate change exposes organisms to multiple, interacting stressors, yet their joint effects on reproduction and inheritance remain poorly understood. This study investigated the interactive effects of acute heat stress and sublethal imidacloprid exposure on the reproductive success of male Drosophila melanogaster and the subsequent fitness of their offspring. We manipulated the gut microbiome of male flies (germ-free or colonized with one or five bacterial species) and subjected them to individual or combined stress. We show that combined stressors act synergistically to reduce male fitness traits, an effect that is partially buffered by higher microbiome diversity. Paternal stress exposure further reduced offspring fertility, demonstrating cross-generational fitness costs largely independent of microbial transmission. Our results underscore the gut microbiome as an important, but stress-sensitive, contributor to host resilience, and demonstrate how multi-stressor interactions can amplify reproductive failure, with broad implications for population persistence and biodiversity loss in a warming, chemically altered world.