Table_1_Elevation Correlates With Significant Changes in Relative Abundance in Hummingbird Fecal Microbiota, but Composition Changes Little.docx

The microbial communities living on and in vertebrate hosts have myriad effects on their hosts, potentially including fitness and speciation. Microbiomes are influenced by both intrinsic (from the host) and extrinsic (from the environment) factors, but the relative contributions of each are unknown for most non-model species. Abiotic environmental factors can influence the microbiome directly but it is less clear how abiotic gradients shape microbiome communities in the wild. Here, we captured eight wild Anna’s hummingbirds from three different elevations along their elevational distribution in California and moved them directly to a middle (“Within Range”) elevation. After some time at this elevation, the birds were moved in captivity to an “Above Range” elevation, and two birds were later moved back to the Within Range elevation. Fecal and food samples were collected longitudinally and the V4 region of the 16S rRNA gene analyzed. The most abundant phyla in all samples were Fusobacteria, Firmicutes, Actinobacteria, and Proteobacteria. Individual Bird ID explained the greatest amount of microbiome variation at 27.5%, signifying some amount of stability in the Anna’s hummingbird fecal microbiome. Sample elevation explained 19.6% (p = 0.001) of the variation using weighted UniFrac, but only 2.0% (p = 0.047) using unweighted UniFrac, implying a change in abundance of bacterial lineages in the microbiome but not in the presence or absence of the microbes. Additionally, Fusobacteria were 7.0x more abundant in the Above Range elevation samples while Firmicutes were 0.3x lower. A thorough understanding of how the environment can shape the microbiome may assist in conservation efforts and a general understanding of host-microbiome relationships in an era of rapid and global environmental change.

栖息于脊椎动物宿主体表与体内的微生物群落，对宿主存在诸多影响，涵盖宿主适合度与物种形成等潜在效应。微生物组（Microbiome）的组成同时受宿主内在因素与环境外在因素共同调控，但针对多数非模式物种而言，二者的相对贡献仍未明确。非生物环境因子可直接作用于微生物组，但目前尚不清楚非生物环境梯度在野生环境中如何塑造微生物群落结构。本研究从加利福尼亚州境内安娜氏蜂鸟（Anna’s hummingbirds）的海拔分布梯度中选取3个点位，捕获8只野生个体，并将其直接转移至该物种分布范围内的中等海拔（"分布范围内"）区域。待蜂鸟适应该海拔环境一段时间后，将其人工转移至高于其分布范围上限的海拔（"分布范围以上"）区域，后续又将其中2只蜂鸟重新转移回中等海拔（"分布范围内"）点位。研究人员纵向收集粪便与食物样本，并对16S核糖体RNA基因（16S rRNA gene）的V4可变区进行扩增子测序分析。所有样本中丰度最高的菌门依次为梭杆菌门（Fusobacteria）、厚壁菌门（Firmicutes）、放线菌门（Actinobacteria）与变形菌门（Proteobacteria）。个体蜂鸟的ID可解释27.5%的微生物组变异，为所有影响因素中占比最高者，这表明安娜氏蜂鸟粪便微生物组存在一定程度的稳定性。基于加权UniFrac距离，采样点海拔可解释19.6%的微生物组变异（p=0.001）；而基于非加权UniFrac距离，该比例仅为2.0%（p=0.047），这意味着环境海拔变化主要引发微生物组中细菌类群的丰度改变，而非类群的有无变化。此外，"分布范围以上"海拔的样本中，梭杆菌门的丰度是中等海拔样本的7.0倍，而厚壁菌门的丰度则仅为中等海拔样本的0.3倍。深入阐明环境如何塑造微生物组，或可为生物保护工作提供理论支撑，亦有助于在全球环境快速变化的当下，进一步理解宿主与微生物组之间的互作关系。