Within a given species, considerable inter-individual, spatial, and temporal variation in the composition of the host microbiome exists. In group-living animals, social interactions homogenize microbiome composition among group members, nevertheless divergence in microbiome composition among related groups arise. Such variation can result from deterministic and stochastic processes. Stochastic changes, or ecological drift, can occur among symbionts with potential for colonizing a host and within individual hosts, and drive divergence in microbiome composition among hosts or host groups. We tested whether ecological drift associated with dispersal and foundation of new groups cause divergence in microbiome composition between natal and newly formed groups in the social spider Stegodyphus dumicola. We simulated the initiation of new groups by splitting field-collected nests into groups of 1, 3, and 10 individuals respectively, and compared variation in microbiome composition among and within groups after 6 weeks using 16S rRNA gene sequencing. Theory predicts that ecological drift increases with decreasing group size. We found that microbiome composition among single founders was more dissimilar than among individuals kept in groups, supporting this prediction. Divergence in microbiome composition from the natal nest was mainly driven by a higher number of non-core symbionts. This suggests that stochastic divergence in host microbiomes can arise during the process of group formation by individual founders, which could explain the existence of among-group variation in microbiome composition in the wild. Individual founders appear to harbour higher relative abundances of non-core symbionts compared with founders in small groups, some of which are possible pathogens. These symbionts vary in occurrence with group size, indicating that group dynamics influence various core and non-core symbionts differently.

中文翻译：

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生态漂变能否解释社会宿主物种群体中微生物组组成的变化？

在给定物种内，宿主微生物组的组成存在相当大的个体间、空间和时间差异。在群体生活的动物中，社会互动使群体成员之间的微生物组组成趋于同质化，但相关群体之间的微生物组组成却出现了差异。这种变化可能是由确定性和随机过程引起的。随机变化或生态漂移可能发生在具有定殖宿主潜力的共生体之间以及单个宿主内部，并导致宿主或宿主群体之间微生物组组成的差异。我们测试了与新群体的扩散和建立相关的生态漂移是否会导致社交蜘蛛Stegodyphus dumicola中出生群体和新形成群体之间微生物组组成的差异。我们通过将现场收集的巢穴分别分成 1 个、3 个和 10 个个体的组来模拟新群体的形成，并使用 16S rRNA 基因测序比较 6 周后组间和组内微生物组组成的变化。理论预测，生态漂变随着群体规模的减小而增加。我们发现，单个创始人之间的微生物组组成比群体中的个体之间的微生物组组成更加不同，这支持了这一预测。微生物组组成与出生巢的差异主要是由更多数量的非核心共生体造成的。这表明宿主微生物组的随机分化可能在个体创始人形成群体的过程中出现，这可以解释野生环境中微生物组组成存在组间变异的原因。与小群体的创始人相比，个体创始人似乎拥有相对丰度更高的非核心共生体，其中一些可能是病原体。这些共生体的出现情况随群体规模的大小而变化，表明群体动态对各种核心和非核心共生体的影响不同。