Fig 2 -

Map of the Rocky Mountain region of the United States, with collection points across the native range of Oreohelix strigosa and their corresponding institution of origin indicated: SBMNH (Santa Barbara Museum of Natural History), UCM (University of Colorado Museum of Natural History), or FMNH (Florida Museum of Natural History).</p

Fig 8 -

(A) Average microbial richness in varying levels of human impact. High human impact populations had significantly higher microbial richness lower levels. Letters indicate significant differences. Error bars indicate standard error. (B) Non-metric multidimensional scaling analysis by site habitat type (PERMANOVA: p-value 2 = 0.09).</p

Alpha-diversity metrics significantly differ by sample types (gut, soil, or vegetation) based on the results of Kruskal-Wallis tests.

Alpha-diversity metrics significantly differ by sample types (gut, soil, or vegetation) based on the results of Kruskal-Wallis tests.</p

Fig 7 -

(A) Average microbial richness in varying habitat complexities. Low habitat complexity had significantly higher richness than high habitat complexity. Letters indicate significant differences. Error bars indicate standard error. (B) Non-metric multidimensional scaling analysis by site habitat complexity level (PERMANOVA: p-value 2 = 0.06).</p

Metadata of all specimens used in this study.

The animal gut microbiome is often a key requirement for host nutrition, digestion, and immunity, and can shift in relation to host geography and environmental factors. However, ecological drivers of microbiome community assembly across large geographic ranges have rarely been examined in invertebrates. Oreohelix strigosa (Rocky Mountainsnail) is a widespread land snail found in heterogeneous environments across the mountainous western United States. It is ideally suited for biogeography studies due to its broad distribution, low migration, and low likelihood of passive transport via other animals. This study aims to uncover large-scale geographic shifts in the composition of O. strigosa gut microbiomes by using 16S rRNA gene sequencing on samples from across its native range. Additionally, we elucidate smaller-scale microbiome variation using samples collected only within Colorado. Results show that gut microbiomes vary significantly across broad geographic ranges. Several possible ecological drivers, including soil and vegetation composition, habitat complexity, habitat type, and human impact, collectively explained 27% of the variation across Coloradan O. strigosa gut microbiomes. Snail gut microbiomes show more similarity to vegetation than soil microbiomes. Gut microbial richness was highest in the rocky habitats and increased significantly in the most disturbed habitats (low complexity, high human impact), potentially indicating signs of dysbiosis in the snails’ gut microbiomes. These small-scale environmental factors may be driving changes in O. strigosa gut microbiome composition seen across large-scale geography. This knowledge will also help us better understand how microbial associations influence species survival in diverse environments and aid wildlife conservation efforts.</div

Fig 4 -

Gut microbiome differences within Colorado by locality: (A) Map of all O. strigosa sampling locations in Colorado (B) Non-metric multidimensional scaling analysis based on collecting locality (PERMANOVA: p-value 2 = 0.31).</p

Relevant metadata from Colorado <i>O</i>. <i>strigosa</i> snail population localities.

Relevant metadata from Colorado O. strigosa snail population localities.</p

Fig 3 -

Gut microbiome differences by state: (A) Relative abundances of the top ten bacterial families contributing to each snail sample set collected from all sampled states (B) Non-metric multidimensional scaling analysis based on state of origin (PERMANOVA: p-value 2 = 0.09). NA refers to taxa that were unresolved at the family level, but were derived from a variety of orders. DEV007 refers to a family within the order Verrucomicrobiales.</p

Differing factors explain gut microbiome variation across <i>O</i>. <i>strigosa</i> samples collected across their native range and within Colorado.

R2 and p-values calculated using Permutational Multivariate Analysis of Variance, with left column as the explanatory variable. Gut microbiome composition is significantly associated with all variables, but most explained by location.</p