Species status of the red-shouldered blackbird (Agelaius assimilis): Implications for ecological, morphological, and behavioral evolution in agelaius

Populations of the Red-winged Blackbird (Agelaius phoeniceus) endemic to Cuba, which are distinct from continental forms in a number of important morphological and behavioral traits, have been recognized as a separate species, the Red-shouldered Blackbird (A. assimilis). We provide the first genetic evidence for species status of A. assimilis, by comparison of mitochondrial DNA sequence from this taxon with variation across the range of A. phoeniceus. The characteristics and phylogenetic placement of A. assimilis significantly complicate previously completed ancestral-state reconstructions for traits associated with mating-system evolution, including the mating system itself, as well as sexual dimorphism and male parental care. Although comparative data are nearly equally consistent with retention of the ancestral states of monogamy and associated characteristics in A. assimilis and with reversal from polygyny back to monogamy in this lineage, we currently favor the reversal scenario on the basis of biogeographic plausibility. Closer study of species-specific behavioral repertoires in this and related species, as well as studies of habitat characteristics and species interactions, should provide additional insights into the factors promoting the evolution of polygyny in this genus.