Modeling the zebrafish gut microbiome's resistance and sensitivity to climate change and parasite infection

As climate change increases global water temperatures, ecologists expect intestinal helminth infection ranges to expand and increase the health burden on aquatic organisms. However, the gut microbiome can interact with these parasites to influence infection outcomes, raising the possibility that its response to increasing temperatures may help buffer against increased infection burden. To evaluate this hypothesis, we sought to determine if the microbiome is resistant or resilient to the stressors of increased water temperature, helminth exposure, and their combination, and whether this variation linked to infection outcomes. We leveraged the zebrafish (Danio rerio) model organism to measure how these variables relate to the temporal dynamics of the gut microbiome. In particular, we exposed adult zebrafish to the parasitic whipworm Pseudocapillaria tomentosa across three different water temperatures (28{degrees}C, 32{degrees}C, 35{degrees}C), and analyzed fecal microbiome samples at five time points across 42 days. Our findings show that parasite exposure and water temperature independently alter gut microbiome diversity. Moreover, we find that water temperature moderates the association between parasite infection and the gut microbiome. Consistent with this observation, but at odds with current expectations, we find that increasing water temperature reduces parasitic infection in fish. Overall, our results indicate that water temperature alters the contextual landscape of the gut microbiome to impact its response to an exogenous stressor of an intestinal parasite in zebrafish. Furthermore, our findings represent the first report of the effects of elevated temperature on parasitic nematode development in a fish host. Importantly, our study demonstrates that climate change may have unanticipated and environmentally contingent impacts to vertebrate gut microbiomes and health outcomes in response to an exogenous stressor.