Does ecological drift explain variation in microbiome composition among groups in a social host species?

Area of Science:

• Ecology
• Microbiology
• Evolutionary Biology

Background:

• Host microbiome composition varies significantly within species.
• Social interactions can homogenize microbiomes within groups, but divergence occurs between groups.
• Microbiome variation arises from deterministic and stochastic processes, including ecological drift.

Purpose of the Study:

• To investigate if ecological drift during group formation causes microbiome divergence in the social spider *Stegodyphus dumicola*.
• To test the prediction that ecological drift increases with decreasing group size.
• To understand the role of dispersal and new group foundation in shaping host microbiomes.

Main Methods:

• Simulated new group formation by splitting field-collected spider nests into groups of 1, 3, and 10 individuals.
• Analyzed microbiome composition after 6 weeks using 16S rRNA gene sequencing.
• Compared microbiome variation among and within newly formed groups.

Main Results:

• Microbiome composition was more dissimilar among single founders than among individuals in larger groups, supporting the ecological drift hypothesis.
• Divergence from natal nest microbiomes was primarily driven by an increase in non-core symbionts.
• Individual founders harbored higher relative abundances of non-core symbionts, including potential pathogens, compared to founders in small groups.

Conclusions:

• Stochastic divergence in host microbiomes occurs during group formation by individual founders.
• Ecological drift can explain among-group variation in host microbiome composition observed in natural populations.
• Group size and dynamics differentially influence the abundance and composition of core and non-core symbionts.