Marmot mass gain rates relate to their group’s social structure

Mass gain is an important fitness correlate for survival in highly
seasonal species. While many physiological, genetic, life history, and
environmental factors can influence mass gain, more recent work suggests
the specific nature of an individual’s own social relationships also
influences mass gain. However, less is known about consequences of social
structure for individuals. We studied the association between social
structure, quantified via social network analysis, and annual mass gain in
yellow-bellied marmots (Marmota flaviventer). Social networks were
constructed from 31,738 social interactions between 671
individuals in 125 social groups from 2002 to 2018. Using a refined
dataset of 1,022 observations across 587 individuals in 81 social groups,
we fitted linear mixed models to analyze the relationship between
attributes of social structure and individual mass gain. We found that
individuals residing in more connected and unbreakable social groups
tended to gain proportionally less mass. However, these results were
largely age dependent. Adults, who form the core of marmot social groups,
residing in more spread apart networks had greater mass gain than those in
tighter networks. Yearlings, involved in a majority of social
interactions, and those who resided in socially homogeneous and stable
groups had greater mass gain. These results show how the structure of the
social group an individual resides in may have consequences for a key
fitness correlate. But, importantly, this relationship was age-dependent.