Adaptation to chronic malnutrition leads to reduced dependence on microbiota in Drosophila

Numerous studies have shown that animal nutrition is tightly linked to gut microbiota, especially under nutritional stress. In Drosophila, microbiota are known to promote juvenile growth, development and survival on poor diets, mainly through enhanced digestion leading to changes in hormonal signaling. Here we show that this reliance on microbiota is greatly reduced in replicated Drosophila populations that adapted to a poor larval diet in the course of over 170 generations of experimental evolution. Protein and polysaccharide digestion in these malnutrition-adapted populations became much less dependent on colonization with microbiota. This was accompanied by changes in at least some targets of dFOXO transcription factor, which is a key regulator of cell growth and survival. Our study suggests that some metazoans have retained the evolutionary potential to adapt their physiology such that association with microbiota may become optional rather than essential.