Abstract and Keywords
The high level of genetic relatedness between parents and offspring is a key feature of family groups and is thought to be a major factor stabilizing social interactions within families. However, these families are only one type of persistent animal social group that strikes a balance between conflict and cooperation. In many species, males aggregate to court females; in a fascinating subset of species, these aggregations also include stable male alliances, and male partners perform elaborate and cooperative courtship displays. These complex social groups provide interesting systems for understanding the costs and benefits of group membership and how group formation occurs. Kinship, a central aspect of traditionally defined families, also exerts an influence in some male–male assemblages, yet the fitness consequences of nepotistic interactions are likely minor in most cases. In many other lekking birds, groupmates are not genetic relatives, and subordinates join male groups to obtain direct or delayed fitness benefits. The manner in which reproduction is shared, and the benefits accruing to subordinates in the group may help to determine how groups form. When kin-selected benefits drive reproductive coalitions, those coalitions can form early in animals’ lives, when exposure to related potential partners is most frequent. However, when subordinate reproductive success is based on other benefits, males seem to choose among groups, sometimes delaying reproduction for years, apparently to find the best available display opportunity. Male display alliances offer an opportunity to investigate the factors stabilizing social interactions outside of a predetermined family structure, and the extent to which similar forces influence family and nonfamily groups. Clearly, leks in general and cooperative male alliances in particular have much to offer as laboratories for studying intrasexual behavior in addition to their well-established utility as model systems for understanding intersexual signaling and mate choice.
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