Evolution of polygyny in the ancestors of red-winged blackbirds

We map behavioral characters related to mating system onto a phylogeny of t he New World blackbirds (family Icteridae) in order to test hypotheses on t he evolution of polygyny in Red-winged Blackbirds (Agelaius phoeniceus). Th e two hypotheses we test are "long-term models" in the sense that, unlike m ost polygyny hypotheses, they allow the ancestral mating system to differ f rom the present one in characters other than female preferences for mated v ersus unmated males. In one model, polygyny evolves from the typical territ orial monogamy system of most terrestrial passerines; in the second model, polygyny evolves from a system resembling that of monogamous Agelaius speci es, with marsh breeding and without male territoriality. Both hypotheses as sume that female-biased parental care coevolves with polygyny. Our reconstr uction suggests that the closest non-polygynous ancestor of Red-winged Blac kbirds was characterized by monogamy, male territoriality, equal sharing of parental care between the sexes, and terrestrial breeding. Further, polygy ny and female-biased care are suggested to have evolved on the same branch as marsh nesting. These results refute our second hypothesis in which polyg yny evolves from "Agelaius monogamy," while providing provisional support f or the first model in which polygyny evolves from territorial monogamy.