Brown bear gut microbiomes: micro-ecological perspectives in wildlife conservation

Sarah Trujillo and Diana J. R. Lafferty, Biology, Northern Michigan University, Marquette, MI, Grant Hilderbrand, National Park Service, Anchorage, AK, Lindsey Mangipane, US Fish and Wildlife Service, Anchorage, AK, Erin McKenney, North Carolina State University, NC, Matthew Rogers, National Oceanic and Atmospheric Administration

Background/Question/Methods
Gut microbiomes (GMBs), complex communities of microorganisms inhabiting the gastrointestinal tracts of their hosts, perform countless micro-ecosystem services such as facilitating energy uptake and modulating immune responses. While scientists increasingly recognize the role GMBs play in host health, the role of GMBs in wildlife ecology and conservation have yet to be realized fully. Using brown bears (Ursus arctos) as an ecological model, we sought to a) assess variation in brown bear GMBs across Alaska and b) evaluate the role that extrinsic factors (e.g., location, diet, and season) play in brown bear GMBs. To achieve these aims, we subsampled brown bear fecal samples collected during United States Geological Survey and National Park Service research activities at three National Parks and Preserves (Gates of the Arctic, Lake Clark, and Katmai). From these fecal samples, we extracted microbial DNA for 16S rRNA amplicon sequencing and microbial taxonomic classification. We analyzed GMB communities using alpha and beta diversity indices (e.g., Faith’s Phylogenetic and Shannon; Bray-Curtis and weighted/unweighted UniFrac). We then used linear mixed models to examine the relationship between alpha diversity and extrinsic factors and Non-metric Multidimensional Scaling (NMDS) to visualize the strength of factors driving variation in GMB diversity.
Results/Conclusions
We found seven major bacterial phyla (i.e., taxa with more than 1% relative abundances) across the study populations, with four phyla (Firmicutes, Proteobacteria, Epsilonbacteraeota, and Actinobacteria) occurring in brown bears in all three National Parks and Preserves. Our results indicate that both location and diet drive GMB variation with bears hosting less phylogenetic diversity as park distance inland increases. Furthermore, Bray-Curtis NMDS plots show distinct clustering at the park level and perMANOVA results show significant differences in GMBs among parks (R2=0.114, p=0.008). Results indicate that brown bears with access to marine resources host more variable and diverse GMB communities. Recognizing which brown bear populations have lower GMB diversity will allow managers to identify populations which may be more sensitive to perturbations (i.e., less resilient) and, subsequently, GMB imbalance that can lead to negative health implications. By integrating macro and micro-ecological perspectives we hope to inform local and landscape-level management decisions to promote long-term brown bear conservation and management.