No abstract

This study is the first to reveal the differential effects of different species of planktonic bacteria on fish kairomone-induced defense traits and energy redistribution in Daphnia . Our results not only help deepen the understanding of Daphnia ’s inducible defenses in environments containing a variety of bacteria but also provide insights into the energy reallocation involved in anti-predator defenses.

Background: Gut microbiota plays an important role in host physiology and fitness. The gut microbiota can promote host health by influencing life history traits, especially in arthropods. However, it is not clear whether the performance of host defense traits in response to predator pressure in natural food webs is related to their gut microbiota composition. In this study, we used Daphnia magna as a model organism to investigate the relationship of D. magna life history traits and gut microbiota alterations under predator kairomone based on 16S rRNA amplicon sequencing.Result: We showed that the microbiota composition of D. magna was significantly affected by their predator risk and development stage. The relative abundance of Comamonadaceae (mainly Limnohabitans sp.) significantly decreased in the presence of predator kairomone. Furthermore, the presence of predator kairomone significantly reduced the α diversity of gut microbiota in D. magna with the increase of instar. Among them, the OTUs belonged to Epsilonbacteraeota and Firmicutes in the presence of predator kairomone were significantly higher than those in the control group. The results of functional predictions showed that predation pressure promote the metabolic function of gut microbiota, such as metabolism of energy, cofactors, and vitamins. By analyzing the correlation between the induced defense traits of D. magna and the relative abundance of bacteria, we found that the increased abundance of Comamonadaceae, Moraxellaceae, and Flavobacteriaceae were linearly correlated with the partial defense traits of D. magna. Specifically speaking, body size was positively correlated with an increased abundance of Comamonadaceae, whereas spine length was negatively correlated with an increased abundance of Comamonadaceae but was positively correlated with increased Flavobacteriaceae abundance. Conclusions: Our results suggested that predation risk can affect the composition of the gut microbiota in D. magna, which may indirectly induce the production of defensive traits in D. magna. The results of this study revealed an important role of gut microbiota in the development of defensive traits of Daphnia in response to fish predators. The correlation between microbial abundance and defense traits is of great significance for further understanding the effect of host-microbiota interaction on individual anti-predation defense.