This study investigated symbiont transmission in the social spider *Stegodyphus dumicola*, focusing on the role of social interactions. The researchers hypothesized that horizontal transmission, enhanced by social interactions, plays a significant role in maintaining stable host-symbiont associations. Three experiments using 16S rRNA gene amplicon sequencing were conducted: (i) life cycle analysis to determine symbiont acquisition timing; (ii) cross-fostering to assess transmission from natal or foster nests; and (iii) mixing adults with different microbiome compositions to observe homogenization. Results show offspring hatch symbiont-free, acquiring symbionts vertically through regurgitation feeding. Social transmission homogenizes microbiome composition among nest mates. The study concludes that high-fidelity social transmission facilitates and maintains stable host-symbiont associations.

Clémence Rose, Marie B. Lund, Andrea M. Søgård, Mette M. Busck, Jesper S. Bechsgaard, Andreas Schramm, Trine Bilde