Applying the coalitionary-traits metric: sociality without cooperation in male yellow-bellied marmots

Mammalian sociality varies both within and between species. We developed a trait-based method to quantify sociality in a continuous way to study the adaptive utility and evolution of male social behavior. The metric is based on 3 key traits--mutual tolerance, collaboration, and partner preference; males with no traits are not social, whereas those with all 3 traits are described as forming coalitions. We applied this framework to systematically describe sociality in the yellow-bellied marmot (Marmota flaviventris). Male marmot sociality varies: social groups contain one to several adult males, who may or may not monopolize reproduction. Through a series of experiments and demographic analyses, we found that male marmots do not appear to discriminate among individuals and thus do not show evidence of partner preference, males do not adjust alarm-calling behavior in a way consistent with male--male collaboration (but may alarm call to preferentially warn kin), and males do not increase their reproductive success by forming multiple-male groups. We conclude that yellow-bellied marmots show rudimentary sociality, with multiple-male groups maintained mainly by an environmental constraint and possible kin selection. The coalitionary-traits metric allowed us to systematically and objectively evaluate the degree of sociality in a socially plastic species. Copyright 2010, Oxford University Press.