The phylogeny of jays in the genus Aphelocoma describes the evolutionary appearance or disappearance of helping and other social behaviors that have been much studied in this genus. Using published allozyme data and new behavioral characters we reexamine the phylogeny of Aphelocoma. The best-fitting hypothesis is that the complex social system of the Mexican Jay (Aphelocoma ultramarina), including delayed maturation, helping, plural breeding, and loss of the rattle call, arose from a simpler state in a jay ancestor, perhaps one that already had occasional nonbreeding associates. The interpretation of phylogeny in eastern populations of the Mexican Jay may be complicated by hybridization with the Scrub Jay (A. coerulescens), suggesting the possibility of reticulate evolution in the genus. The Florida Scrub Jay (A. c. coerulescens) appears to be closely related to the population of Scrub Jays in southern Mexico, and together the two constitute a distinct clade within the Scrub Jay superspecies.
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