Phylogeny and Historical Biogeography of Steamer-Ducks (Anatidae: Tachyeres)

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Abstract
An earlier phylogenetic analysis of morphological characters (Livezey, 1986a) indicates that Tachyeres is a member of a specialized clade of Southern Hemisphere shelducks (Tadorninae). Within Tachyeres, the three flightless species appear to be monophyletic, with the two Atlantic species.sbd.T. leucocephalus and T. brachypterus.sbd.being closest relatives. This phylogenetic hypothesis mirrors the pattern of morphometric similarities among the four species. Speciation in the genus is explainable by the isolation caused by two major glaciations in southern South America and related fluctuations in sea level, and intervening dispersals. The biogeographic model is compared to a morphometric assessment of populations of T. patachonicus and electrophoretic analyses of the four species of Tachyeres.