Deviations from an individual’s average sociality have fitness consequences

Social relationships are consequential and affect survival, longevity and reproductive success in many species. Prior studies have successfully identified the fitness consequences of variation in sociality relative to other individuals. However, we have yet to quantify the fitness consequences of social variation within an individual over time. By using a within-individual centering approach, we can identify the consequences of deviations from an individual’s ‘average’ sociality. This approach has not been applied to the study of animal sociality. We used 20 years of data from a population of yellow-bellied marmots ( Marmota flaviventer ) to understand the fitness consequences of an individual’s average affiliative social network position over their lifetime, and of individuals’ annual deviations from their average social position. We found that an individual’s deviation from its average sociality was very strongly associated with both winter and summer survival. Deviations from some average measures of sociality were also associated with the likelihood of reproducing, but not in a consistent direction. Lifetime average social network positions had limited associations with survival and reproduction. Interestingly, litter size results varied between males to females; neither lifetime averages of social network traits nor deviations from these averages were associated with litter size in females, but deviations in sociality were associated with larger numbers of weaned offspring in males. Future studies of the consequences of social relationships may benefit from the use of an individual-centering approach, and further work is required to understand the environmental and social drivers of this intra-individual adaptive plasticity.