Abstract: The gut microbiota plays a crucial role in host physiological function and ecological adaptation. Investigating the impact of different habitat types and seasonal changes on its structure is of significant scientific importance for revealing the host-microbe interaction mechanism. This study collected fecal samples from Brandt’s voles (Lasiopodomys brandtii) under summer field, winter field, and summer indoor conditions, and analyzed the composition, co-occurrence network, assembly mechanism, and predicted metabolic function of the gut microbiota based on 16S rRNA gene amplicon sequencing. The results showed that both seasonal changes and habitat type significantly shaped the gut microbiota of Brandt’s voles, with seasonal factors having a more pronounced effect. In terms of habitat comparison, wild summer individuals, due to highly heterogeneous food intake and complex environmental stimuli, exhibited significantly higher alpha diversity and co-occurrence network complexity of gut microbiota than indoor summer individuals. Their community assembly was primarily driven by deterministic processes (homogeneous selection accounted for 77. 8%), while indoor individuals, living in a constant environment for extended periods, showed a looser network structure, with assembly patterns shifting towards stochastic processes (71. 1%). In terms of seasonal comparison, winter wild individuals showed the lowest microbial diversity, with a dramatic restructuring of the core microbial community. The relative abundance of Bacillota and other phyla decreased significantly, while Bacteroidota (mainly the family Muribaculaceae) experienced an explosive increase, leading to a significant decrease in the Bacillota/Bacteroidota ratio. Although the microbial network shrank in winter, its local aggregation (clustering coefficient) and the importance of key nodes increased significantly, intensifying antagonistic competition. Furthermore, community assembly mechanism analysis revealed that environmental directional selection pressure weakened from summer to winter, while the relative contribution of stochastic processes such as ecological drift increased. Functional predictions indicate that extreme winter cold and food scarcity broadly inhibited the basal metabolism and tricarboxylic acid cycle of the gut microbiota, while activating specific degradation pathways, such as D-arabinose and glycolic acid metabolism, to maintain host energy homeostasis. Furthermore, the outdoor environment, compared to indoor conditions, induced metabolic potential in the gut microbiota for cellular defense and multinutrient utilization, including cell membrane or wall synthesis and specific amino acid degradation. This study systematically reveals the structural reorganization and simultaneous functional remodeling of the gut microbiota of Brandt’s voles under extreme resource and environmental stress, providing important evidence for a deeper understanding of the ecological adaptation strategies of wild animals and host-microbe interactions.

Key words: Brandt’s vole (Lasiopodomys brandtii), Gut microbiota, Habitat type, Seasonal change

摘要： 肠道微生物在宿主生理功能及生态适应中发挥了关键作用，探究不同生境类型及季节变化对其结构的影响，对于揭示宿主-微生物互作机制具有重要科学意义。本研究采集了夏季野外、冬季野外以及夏季室内条件下布氏田鼠（Lasiopodomys brandtii）的粪便样品，并基于16S rRNA基因的扩增子测序分析其肠道微生物的组成、共现网络、组装机制及预测代谢功能。结果表明，季节变化与生境类型均能显著塑造布氏田鼠的肠道微生物，且季节因素的影响更为显著。在生境对比方面，野外夏季个体由于高异质性的食物摄入及复杂的环境刺激，其肠道微生物的α多样性和共现网络复杂度显著高于室内夏季个体，其群落组装主要受确定性过程驱动（同质选择占比77.8%），而长期处于恒定环境下的室内个体其网络结构趋于松散，组装模式向随机性过程（占71.1%）转变。在季节对比方面，冬季野外个体的菌群多样性降至最低，且核心菌群结构发生剧烈重构：芽孢杆菌门（Bac-illota）等菌群相对丰度大幅降低，而拟杆菌门（Bacteroidota，主要为鼠杆菌科Muribaculaceae）暴发式升高，导致芽孢杆菌门/拟杆菌门比值大幅下降。尽管冬季菌群网络规模收缩，但其局部聚集度（聚类系数）和关键节点的重要度显著增加，拮抗竞争加剧。此外，群落组装机制分析显示，从夏季到冬季环境定向选择压力减弱，生态漂变等随机过程的相对贡献有所增加。功能预测表明，冬季极寒和食物匮乏对菌群的基础代谢和三羧酸循环产生了广泛的抑制作用，但靶向激活了D-阿拉伯糖和乙醇酸代谢等特殊降解通路以维持宿主能量稳态；而野外环境相比室内则诱导了菌群在细胞膜/细胞壁合成及特定氨基酸降解等细胞防御与多元营养利用上的代谢潜能。本研究系统揭示了布氏田鼠肠道微生物在极端资源及环境压力下的结构重组与功能同步谱系重塑，为深入理解野生动物的生态适应策略和宿主-微生物互作关系提供了重要依据。

关键词: 布氏田鼠, 肠道微生物, 生境类型, 季节变化