Genotype specific and microbiome effects of hypoxia in Daphnia magna phenotypes.

The fitness of the host is highly influenced by the interplay between hosts and their microbiota. The flexivle nature of these microbiota enables them to respond swiftly to shifts in the environment, which plays a key role in the host its capacity to withstand environmental stresses. To understand the role of the microbiome in host tolerance to hypoxia, one of the most significantly chemical changes occurring in water ecosystems due to climate change, we performed a reciprocal gut transplant experiment with the freshwater crustacean Daphnia magna. In a microbiome transplant experiment, two genotypes of germ-free recipients were inoculated with gut microbiota from Daphnia donors of their own genotype or from the other genotype, that had been either pre-exposed to normoxic or hypoxic conditions. Here we found that Daphnia magna individuals have a higher survival probability in hypoxia if their microbiome has been pre-exposed to hypoxia and that the bacterial communities of the recipients change over time with a reduction in alpha diversity, which seems to be stronger when donors were pre-exposed to a hypoxic environment. While donor genotype had no influence on longer term survival probability in hypoxia, donor genotypes is the most influential factor of the microbial community three days after the transplantation. Our results indicate that microbiome influencing factors mediate host fitness in a hypoxic environment in a time depending way.