Data from: The index case is not enough: variation among individuals, groups, and social networks modify bacterial transmission dynamics

1.The traits of the index case of an infectious disease outbreak, and the
circumstances for their etiology, potentially influence the trajectory of
transmission dynamics. However, these dynamics likely also depend on the
traits of the individuals with whom the index case interacts. 2.We used
the social spider Stegodyphus dumicola to test how the traits of the index
case, group phenotypic composition, and group size interact to facilitate
the transmission of a GFP-labeled cuticular bacterium. We also compared
bacterial transmission across experimentally generated “daisy-chain”
versus “star” networks of social interactions. Finally, we compared social
network structure across groups of different sizes. 3.Groups of 10 spiders
experienced more bacterial transmission events compared to groups of 30
spiders, regardless of groups’ behavioral composition. Groups containing
only one bold spider experienced the lowest levels of bacterial
transmission regardless of group size. We found no evidence for the traits
of the index case influencing any transmission dynamics. In a second
experiment, bacteria were transmitted to more individuals in
experimentally induced star networks than in daisy-chains, on which
transmission never exceeded three steps. In both experimental network
types, transmission success depended jointly on the behavioral traits of
the interacting individuals, however, the behavioral traits of the index
case were only important for transmission on star networks. 4.Larger
social groups exhibited lower interaction density (i.e. had a low ratio of
observed to possible connections) and were more modular, i.e., they had
more connections between nodes within a sub-group and fewer connections
across sub-groups. Thus, larger groups may restrict transmission by
forming fewer interactions and by isolating sub-groups that interacted
with the index case. 5.These findings suggest that accounting for the
traits of single exposed hosts has less power in predicting transmission
dynamics compared to the larger-scale factors of the social groups in
which they reside. Factors like group size and phenotypic composition
appear to alter social interaction patterns, which leads to differential
transmission of microbes.