Rana temporaria gut microbiome - temperature and nitrate effects
Nitrate pollution and increased temperatures due to climate change are ubiquitous stressors likely to interact and affect the health and survival of wildlife, particularly aquatic ectotherms. Commensal/symbiotic microorganisms (microbiome) that inhabit animal bodies may contribute to the maintenance of their health under such stressful circumstances. We conducted a common-garden experiment crossing three nitrate levels (0, 50, 100 mg/L) and five temperature treatments (18 °C, 22 °C, 26 °C, 28 °C, and a temperature fluctuation regime: 17–26.5 °C) to investigate the interactive and individual effects of these stressors on health biomarkers (water-borne corticosterone, body condition, and developmental rate) of an aquatic ectotherm and on its gut microbiome diversity and composition, using amphibian larvae as model organisms. All biomarkers reflected levels of pollution and thermal stress imposed on larvae, the outcomes being more likely explained by changes in microbiome composition than diversity. Based on detected OTUs, we predicted an increase in the nitrate reduction pathway and decrease in several nucleotide biosynthesis pathways with increasing nitrate pollution, and alterations in several degradation pathways with increasing temperature. We urge for studies investigating the effects of different environmental conditions on microbiome composition and consequences for host health in a world threatened by biodiversity loss.