Host-symbiotic microbial community interaction and adaptation to environmental stress in the water flea Daphnia

Every organism is host to a diverse and dynamic symbiotic microbial community (SMC). The wide array of genotypes presented by SMCs and their ability to adapt rapidly to novel conditions combined with host control over the microbiota could help to maximize host fitness. Further, the nature and outcome of these symbiotic interactions are often context-dependent. Using exposure to toxic substances of natural and anthropogenic origin as key environmental stressor and the water flea Daphnia, we here want to investigate the interaction between host genotype (G), environmental (E) stress and GxE interactions on SMCs. Via standardized cohort life table experiments, we will expose clone sets of axenic Daphnia to diverse naturally occurring microbial communities and to toxic stress to unravel what the role of the SMC is in host adaptation to these stressors. We further aim to investigate what the impact is of the SMC and stress-induced changes in the SMC on host-parasite interactions. It is currently not known how environmental stress affects symbiotic microbiota and host-SMC interactions or what the consequences of SMCs are for adaptation in natural ecosystems. If our study reveals strong associations between SMCs and the investigated stressors, it may change evolutionary paradigms, in the sense that the unit of selection may not be the host genome only. The unique perspective of our study is that we can investigate this in vivo and in real-time. In this way, we will be able to obtain insight into how hosts and their SMCs may function in natural ecosystems. Understanding how environmental change and host genotype affect SMCs, and ultimately host performance, is essential for different fields ranging from ecology and evolution to ecotoxicology, conservation biology and medicine.