Role of gut microbiota in driving adaptation to changing and polluted environments: the case of Daphnia adaptation to cyanobacterial harmful algal blooms.

The gut microbiota is an important source of metabolic innovations for animal hosts, and is increasingly considered as a key factor that may drive adaptation to the fast and drastic environmental changes imposed by human activities and global warming. This emerging hypothesis, however, lacks strong empirical support. Predicting how, and to what extent, the gut microbiota may drive adaptation requires to understand how gut symbionts affect host phenotype, and to decipher the functional mechanisms that recruit and organize this microbial community. Here, I propose to address these questions, using the freshwater crustacean Daphnia and its adaptation to toxic cyanobacteria harmful algal blooms (cyanoHABs) as a model system. CyanoHABs have strongly increased in frequency and intensity as a result of eutrophication and climate change, and pose severe threat on aquatic ecosystems. I have previously shown, through gut microbiota transplants, that resistance to cyanobacteria in Daphnia is mediated by genotypedependent gut microbiota. Capitalizing on this unique system, I propose here to unravel the functional mechanisms underlying both the establishment of these mutualistic gut symbionts (focusing on the immune factors that structure the microbiota) and their ability to drive adaptation to cyanobacteria. This project will provide key novel insights into the understanding of host-microbiota interactions, and impact diverse fields, from ecology and evolutionary biology to medicine.