favors the early emergence of fit and fertile adult upon chronic undernutrition.

Animals are naturally surrounded by a variety of microorganisms with which they constantly interact. Among these microbes, some live in close association with a host and form its microbiota. These communities are being extensively studied, owing to their contributions to shaping various aspects of animal physiology. One of these commensal species, , and in particular the strain, has been shown to promote the growth of larvae upon nutrient scarcity, allowing earlier metamorphosis and adult emergence compared with axenic individuals. As for many insects, conditions surrounding the post-embryonic development dictate key adult life history traits in , and adjusting developmental timing according to the environment is essential for adult fitness. Thus, we wondered whether the growth acceleration induced by in a context of poor nutrition could adversely impact the fitness of adults. Here, we show that the -mediated acceleration of growth is not deleterious; adults emerging after an accelerated development are as fit as their axenic siblings. Additionally, the presence of even leads to a lifespan extension in nutritionally challenged males. These results demonstrate that is a beneficial partner for through its entire life cycle. Thus, commensal bacteria allow the earlier emergence and longer survival of fit and fertile individuals and might represent one of the factors contributing to the ecological success of .