New phylogenetic information suggests both an increase and at least one loss of cooperative breeding during the evolutionary history of Aphelocoma jays

Efforts to identify ecological and life history factors associated with cooperative breeding have been largely unsuccessful, and interest is growing in the role of phylogenetic history in determining the distribution of this social system among lineages. In birds, cooperative breeding is distributed non-randomly among lineages, suggesting that phylogenetic inertia may play an important role in determining its distribution. The bird genus Aphelocoma has been particularly well studied because, although it is a relatively small genus, it shows broad among-lineage variation in level of cooperation. Previous analyses described an unusual unidirectional pattern of evolutionary loss of cooperation in Aphelocoma. Here, historical reconstructions based on new phylogenetic data suggest that evolutionary changes in cooperation have been bidirectional, with at least one gain and at least one loss over relatively recent timescales. This result emphasizes that, although history plays an important role in determining the incidence of cooperative breeding, cooperative behavior can switch relatively quickly in evolutionary time and may be influenced by the ecological context within which particular populations are distributed.