title: Infectious disease and group size: more than just a numbers game.
abstract: Increased risk of infectious disease is assumed to be a major cost of group living, yet empirical evidence for this effect is mixed. We studied whether larger social groups are more subdivided structurally. If so, the social subdivisions that form in larger groups may act as barriers to the spread of infection, weakening the association between group size and infectious disease. To investigate this 'social bottleneck' hypothesis, we examined the association between group size and four network structure metrics in 43 vertebrate and invertebrate species. We focused on metrics involving modularity, clustering, distance and centralization. In a meta-analysis of intraspecific variation in social networks, modularity showed positive associations with network size, with a weaker but still positive effect in cross-species analyses. Network distance also showed a positive association with group size when using intraspecific variation. We then used a theoretical model to explore the effects of subgrouping relative to other effects that influence disease spread in socially structured populations. Outbreaks reached higher prevalence when groups were larger, but subgrouping reduced prevalence. Subgrouping also acted as a 'brake' on disease spread between groups. We suggest research directions to understand the conditions under which larger groups become more subdivided, and to devise new metrics that account for subgrouping when investigating the links between sociality and infectious disease risk.
authors: Department of Evolutionary Anthropology, Duke University, Box 90383, Durham, NC 27708, USA Duke Global Health Institute, Duke University, 310 Trent Drive, Durham, NC 27710, USA charleslnunn@gmail.com.
authors: Charles L
authors: CL
authors: Nunn
authors: The Microsoft Research-University of Trento COSBI, Piazza Manifattura 1, 38068 Rovereto, Italy Balaton Limnological Institute, Centre for Ecological Research HAS, Klebelsberg K. u. 3, 8237 Tihany, Hungary.
authors: Ferenc
authors: F
authors: Jordán
authors: Department of Human Evolutionary Biology, Harvard University, Cambridge, MA 01238, USA.
authors: Collin M
authors: CM
authors: McCabe
authors: National Evolutionary Synthesis Center, Duke University, Durham, NC 27705, USA.
authors: Jennifer L
authors: JL
authors: Verdolin
authors: School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
authors: Jennifer H
authors: JH
authors: Fewell
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D003141:Communicable Diseases / Q000209:etiology* / Q000635:transmission; D007448:Invertebrates; D008954:Models, Biological; D011156:Population Density; D012307:Risk Factors; D012919:Social Behavior; D013045:Species Specificity; D014714:Vertebrates
keywords: comparative analysis; infectious disease; meta-analysis; social network; social structure; sociality