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.

动物肠道微生物组通常是宿主营养获取、消化与免疫功能的关键必要条件，且会随宿主所处的地理环境与各类环境因子发生变化。然而，针对大地理尺度范围内微生物群落组装的生态驱动因子，无脊椎动物类群的相关研究尚属罕见。Oreohelix strigosa（Rocky Mountainsnail，落基山蜗牛）是一种广布性陆生蜗牛，栖息于美国西部山区各类异质环境中。该物种因分布范围广泛、迁移能力较弱且极少通过其他动物进行被动传播，非常适合生物地理学相关研究。本研究通过对其原生分布范围内的所有采样样本进行16S rRNA基因测序，旨在揭示O. strigosa肠道微生物组组成的大尺度地理变化规律。此外，本研究还利用仅在科罗拉多州境内采集的样本，解析了该物种肠道微生物组的小尺度变异特征。研究结果表明，肠道微生物组在大地理尺度上存在显著差异。包括土壤与植被组成、生境复杂度、生境类型以及人类活动影响在内的多项潜在生态驱动因子，共同解释了科罗拉多州境内O. strigosa肠道微生物组27%的变异来源。蜗牛肠道微生物组与植被微生物组的相似性高于其与土壤微生物组的相似性。肠道微生物群落丰富度在岩石生境中最高，而在受干扰程度最高的生境（复杂度低、人类活动影响强）中则显著升高，这或提示蜗牛肠道微生物组存在菌群失调迹象。这些小尺度环境因子，或正是驱动O. strigosa肠道微生物组组成在大地理尺度上发生变化的核心因素。本研究成果还有助于我们进一步理解微生物共生关系如何影响物种在多样环境中的存活能力，并为野生动物保护工作提供理论支撑。