Variation in the gut microbiota of wild Eurasian otter (Lutra lutra) likely reflects diet shifts between snow-free and snow seasons

The gut microbiota plays an important role in mediating the physiology, immunity, growth and development of animals. The composition of animals’ gut microbiota can be used to make a reasonable assessment of their state of health. The Eurasian otter (Lutra lutra) is a semi-aquatic freshwater top predator. In recent years, its population has declined sharply due to human disturbance, and many populations are on the verge of extinction. Conducting research on the gut microbiota of Eurasian otters in their native environment can reveal the composition and function of their intestinal microorganisms, and provide comparative data for future assessment of the impact of disturbance on otters. Based on this, we collected fecal samples in a national park in northeast China where human interference was absent. A total of 32 and 36 otter feces were collected systematically during the snow season and snow-free season, respectively. We used high-throughput sequencing technology to sequence the V3-V4 region of the 16S rRNA gene and compared the microbial communities. The composition of the otter gut microbiota varied significantly between the two seasons, and alpha diversity of the microbiota in the snow-free season was higher than that in the snow season. In the snow-free season, Firmicutes was identified as the dominant phylum and Romboutsia as the dominant genus, similar to the microbiota of fish, which is the otters’ primary prey. In the snow season, the Proteobacteria and Pseudomonas were identified as the dominant phylum and genus, respectively, likely attributable to the shift toward high-fat diet induced by cold stress. These results indicate that seasonal variations in otter diet and related factors are important causes of changes in otter gut microbiota. The variations in the gut microbiota of wild Eurasian otters may reflect changes in nutritional composition of seasonal prey. Moreover, our findings function as a reference for the protection of gut microbial health in Eurasian otters. Aberrations in the gut microbial composition of urban-dwelling otters may serve as indicators of waterway pollution (such as chemical and microplastic contamination) and nutritional challenges in the future. Against this backdrop, investigations into the gut microbiota of otters living in regions affected by human activities can offer deeper insights into their microbial communities and the molecular mechanisms underlying their environmental adaptation.