The primary case is not enough: Variation among individuals, groups and social networks modify bacterial transmission dynamics

Abstract

The traits of the primary case of an infectious disease outbreak, and the circumstances for their aetiology, potentially influence the trajectory of transmission dynamics. However, these dynamics likely also depend on the traits of the individuals with whom the primary case interacts.We used the social spider Stegodyphus dumicola to test how the traits of the primary case, group phenotypic composition and group size interact to facilitate the transmission of a GFP-labelled cuticular bacterium. We also compared bacterial transmission across experimentally generated “daisy-chain” vs. “star” networks of social interactions. Finally, we compared social network structure across groups of different sizes.Groups of 10 spiders experienced more bacterial transmission events compared to groups of 30 spiders, regardless of groups’ behavioural 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 primary 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 behavioural traits of the interacting individuals; however, the behavioural traits of the primary case were only important for transmission on star networks.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 subgroup and fewer connections across subgroups. Thus, larger groups may restrict transmission by forming fewer interactions and by isolating subgroups that interacted with the primary case.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.

Using multilayer network analysis to explore the temporal dynamics of collective behavior

“…(2019) . These data were previously used by Keiser et al. (2017) to examine global network structures (density and modularity) and Hunt et al.…”

“… Hunt et al. (2019) defined an interaction as a physical contact between any body parts of 2 spiders while stationary in the retreat web (see also Keiser et al. 2017 ; Hunt et al.…”

Social interactions shape individual and collective personality in social spiders

“…Each spider's boldness was measured once a week using an established assay that recorded the recovery of a spider from exposure to air puffs, which mimic the approach of an avian predator [33]. After placing spiders individually in a plastic container (15 Â 15 cm), we waited for 30 s until the spiders were acclimated and stopped moving around the arena, as in recent studies [38,[42][43][44]. We then administered two puffs of air to the anterior prosoma using an infant nose-cleaning bulb.…”

Animal host–microbe interactions

“…Mihaljevic, Hoye, and Johnson () extended this to also consider the role of alternate host species, in conjunction with environmental factors, in shaping symbiont communities across populations of a focal host species. Within a host species, the spatial and hierarchical structure of social interactions was also shown to shape the transmission of individual microbes (and disease susceptibility) in populations (Keiser, Pinter‐Wollman, Ziemba, Kothamasu, & Pruitt, ; Keiser et al., ; Raulo, ), as were several different types of indirect interactions. For instance, parents were found to play a role in shaping the gut microbiota of their offspring even when they were separated from them in space and time, through diapause (Mushegian, Walser, Sullam, & Ebert, ), and to play an active role in modifying the microbiota on the external surface of other (dead) animals in preparing a carcass for their larval offspring (Duarte, Welch, Swannack, Wagner, & Kilner, ).…”