Social structure and close contact between individuals may influence gut microbiome composition, according to a study of a wild bird population that examined how microbes are shared within social groups.
Researchers studied the Seychelles warbler, a cooperatively breeding species in which individuals live in small, stable groups and interact at different levels of intensity. Using fecal samples from more than 300 birds, the team performed 16S rRNA sequencing to assess how gut microbiomes vary with social behavior.
The results showed that individuals within the same social group had more similar gut microbiome composition than those from different groups. This pattern remained after accounting for relatedness, suggesting that both shared environment and direct interaction contribute to microbial similarity.
To better understand transmission pathways, the investigators separated bacteria into two groups: aerotolerant organisms, which can survive outside the host, and anaerobic organisms, which are more sensitive to oxygen.
Both bacterial types were more similar within groups than between groups. However, only anaerobic bacteria showed a clear association with the degree of social interaction. Birds that had closer contact – such as breeding pairs and helpers that share nest duties – had more similar anaerobic microbiomes than individuals that interacted less frequently.
In contrast, aerotolerant bacteria did not vary significantly with interaction strength, consistent with environmental acquisition, such as through shared diet or habitat.
The study also found that overall microbial diversity was not strongly associated with social structure. Instead, differences were seen in the composition of microbial communities. This distinction may be relevant when interpreting microbiome data, as similar diversity measures do not necessarily indicate similar microbial profiles.
The findings highlight that microbiome composition can reflect patterns of host interaction and exposure. Variation in microbial profiles may not be solely related to host biology or disease but may also be influenced by social and environmental factors.
Although conducted in a non-human model, the study provides insight into how microbes – particularly anaerobic organisms – may be transmitted through close contact. The authors note that further studies are needed to determine how these findings translate to human populations and clinical settings.
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