Fish predation risk alters the microbiota of Daphnia in the process of inducing its life-history defence traits

1. Host-associated microbiota is an essential mediator of host adaptation to changeable environmental conditions. However, whether fish predation risk alters the gut microbiota composition of Daphnia while also of inducing Daphnia's life-history defence traits remains unclear. Examination of the effect of predation risk on prey-associated microbiota may help in improving our understanding of induced anti-predation defence from a microbial perspective. 2. In this study, Daphnia magna was used as the model organism to investigate the changes in the microbiota in the gut of Daphnia as well as in the whole Daphnia and the culture medium during D. magna life-history anti-predation defence. The relationship of these changes with the development stage was also assessed. 3. The results showed that predation risk can simultaneously induce anti-predation defences and reshape the associated microbiota composition of Daphnia. The gut microbiota of D. magna responded to both developmental stages and predation risk. The Shannon diversity of gut microbiota under predation risk decreased significantly with developmental stage. The abundance of dominant bacteria such as Burkholderiaceae and Flavobacteriaceae decreased under predation risk and was further reduced with developmental stage. Functional prediction results showed that the presence of predation risk mainly weakened overall microbial function, especially metabolic function, in the gut of D. magna. The weakening of microbial function was most obvious during sexual maturity. In addition, the number of unique operational taxonomic units in the whole Daphnia and dissected guts under predation risk was significantly higher than those in control. Based on the screening results, the Pantoea genus (Erwiniaceae family) can clearly distinguish dissected gut samples with or without predation risk. 4. The present study provided more insights into the structural features and functional roles of the Daphnia microbiota and improved our understanding of induced anti-predation defence from a microbial perspective. Furthermore, this study highlights the possible complex correlations that exist between induced defensive traits and altered microbiota, which warrants further investigation.