Phylogenetic and ecological aspects of cooperative breeding in the bee-eaters (Aves: Meropidae)

Abstract

Cooperative breeding (CB) is found in a wide diversity of avian lineages and can be explained at several levels of analysis. After a brief introduction to the theory explaining CB, I take an historical approach to examine CB evolution in the bee-eaters (Family Meropidae). Parsimony analyses of plumage color and shape characters yielded a number of phylogenetic hypotheses. The best supported phylogenies are six fully resolved trees from three analyses and a strict consensus tree from another analysis. These trees are used to examine the possible patterns of evolution in CB and how transition correspond to transitions in other ecological and behavioral traits. Bee-eaters were also studied in Thailand. Little green bee-eaters, Merops orientalis, breed cooperatively and predation pressure may be high in this species. Blue-tailed bee-eaters, M. philippinus, breed cooperatively in dense colonies and show signs of potential extra-pair copulation and intraspecific brood parasitism. Observations of the bay-headed bee-eater, M. leschenaulti, and the blue-bearded bee-eater, Nyctyornis athertoni, document CB in the former and support non-CB designation for the latter. Cooperative breeding is either primitive in bee-eaters or evolved early in the family. Reversals to non-CB occurred in one to three lineages. Transitions in breeding systems are not generally correlated with the transitions in nesting requirements, habitat utilization, migratory behavior, or diet. Evidence suggests correlated evolution between CB and both foraging mode (weak evidence) and social systems (stronger support). This study does not support any single hypothesis for the adaptive basis of CB across the family. Social system evolutionary patterns do suggest the importance of kin selection in several lineages. Lack of change in breeding systems, given diverse ecological and behavioral circumstances, means either cooperative breeding is malleable (selectively advantageous in a variety of ecological conditions) or represents phylogenetic inertia. A final analysis demonstrates that phylogenetic confidence indices fail to express the degree to which characters in a matrix are non-conflicting and congruent (for a given level of noise) and show only limited abilities to distinguish among probabilities of analyses making type II errors.