The effect of hypoxia on Daphnia magna performance and its associated microbial and bacterioplankton community: A scope for phenotypic plasticity and microbiome community interactions upon environmental stress?

The depletion of oxygen as a result of increased stratification and decreased oxygen solubility is one of the most significant chemical changes occurring in aquatic ecosystems as a result of global environmental change. Hence, more aquatic organisms will be exposed to hypoxic conditions over time. Deciphering the effects of hypoxia on strong ecological interactors in this ecosystem's food web is critical for predicting how aquatic communities can respond to such an environmental disturbance. Here (sub-)lethal effects of hypoxia and whether these are genotype specific in Daphnia, a keystone species of freshwater ecosystems, are studied. This is especially relevant upon studying genetic responses with respect to phenotypic switches upon environmental stress. Further, we investigated the effect of hypoxia on the Daphnia microbial community to test if the microbiome plays a role in the phenotypic switch and tolerance to hypoxia. For this, two Daphnia genotypes were exposed for two weeks to either hypoxia or normoxia and host performance was monitored together with changes in the host associated and free-living microbial community after this period. We detected phenotypic plasticity for some of the tested Daphnia performance traits. The microbial community of the bacterioplankton and Daphnia associated microbial community responded via changes in species richness and community composition and structure. The latter response was different for the two genotypes suggesting that the microbiome plays an important role in phenotypic plasticity with respect to hypoxia tolerance in Daphnia, but further testing (e.g., through microbiome transplants) is needed to confirm this.

Automated summary

The depletion of oxygen due to increased stratification and decreased solubility is a significant chemical change in aquatic ecosystems under global environmental change, leading to increased exposure of aquatic organisms to hypoxic conditions. Understanding the effects of hypoxia on key ecological species and their microbial communities is crucial for predicting the response of aquatic communities to this environmental disturbance. In this study, the (sub-)lethal effects of hypoxia on Daphnia, a keystone species in freshwater ecosystems, were examined, along with the potential role of the microbial community in the phenotypic switch and tolerance to hypoxia. The results showed phenotypic plasticity in Daphnia performance traits, as well as changes in species richness and community composition of the microbial community, suggesting the importance of the microbiome in phenotypic plasticity and hypoxia tolerance in Daphnia.