Microbial symbionts can modulate host interactions with biotic and abiotic factors. Such interactions may affect the evolutionary trajectories of both host and symbiont. Wolbachia protects Drosophila melanogaster against several viral infections and the strength of the protection varies between variants of this endosymbiont. Since Wolbachia is maternally transmitted, its fitness depends on the fitness of its host. Therefore, Wolbachia populations may be under selection when Drosophila is subjected to viral infection. Here we show that in D . melanogaster populations selected for increased survival upon infection with Drosophila C virus there is a strong selection coefficient for specific Wolbachia variants, leading to their fixation. Flies carrying these selected Wolbachia variants have higher survival and fertility upon viral infection when compared to flies with the other variants. These findings demonstrate how the interaction of a host with pathogens shapes the genetic composition of symbiont populations. Furthermore, host adaptation can result from the evolution of its symbionts, with host and symbiont functioning as a single evolutionary unit. Author Summary Animals live in close association with microbial partners that can shape many aspects of their lives. For instance, several insects carry bacteria that defend them against parasites and infectious diseases. The intracellular bacterium Wolbachia protects the fruit fly Drosophila melanogaster against viral infection. Natural populations of Drosophila carry different variants of Wolbachia , which differ from one another in the strength of this protection. Here we show that a population of Drosophila infected with viruses during several generations adapts to this challenge through turnover in Wolbachia composition. The Wolbachia variants that give higher protection to viruses, by increasing fly survival and fecundity upon infection, are strongly selected. This work demonstrates that the interaction of an animal with a pathogen can shape its associated microbial populations. We show that adaptation to pathogens can be achieved not only through selection of resistance on the host proper but also through the evolutionary shaping of its microbial community.
【초록키워드】 viruses, Evolution, viral infection, Infectious diseases, Diseases, Genetic, variant, Infection, parasites, virus, viral infections, variants, Population, survival, Viral, pathogen, animal, Factors, trajectory, Pathogens, Bacteria, Fertility, host adaptation, fitness, adaptation, microbial community, association, Interaction, fixation, microbial, natural population, Drosophila melanogaster, natural populations, strength, Drosophila, other variants, increased survival, insect, parasite, Wolbachia, turnover, fecundity, Drosophila C virus, symbiont, Host, Affect, populations, PROTECT, selected, virus, transmitted, modulate, defend, Fly, 【제목키워드】 Viral,