Phylogeny and Biogeography of Dabbling Ducks (genus: Anas): a Comparison of Molecular and Morphological Evidence

--We constructed a phylogeny for the dabbling ducks (tribe Anatini) based on cytochrome-b and ND2 mitochondrial gene DNA sequences. This phylogeny differed in several important respects from a morphological phylogeny developed by Livezey (1991), including the distinctiveness ofthe blue-winged ucks from other dabbling ducks, the inclusion of the genus Tachyeres and exclusion of Callonetta from the subtribe Anateae, and the lack of support for Mareca s a genus separate from Anas. Characters from three other data sets showed greater consistency with the molecular topology than with the morphological topology. The molecular phylogeny divides the dabbling ducks into four distinct groups: (1) four South American genera, including Amazonetta, Lophonetta, Speculanas, nd Tachyeres; (2) the Baikal Teal (Anas formosa); (3) the blue-winged ducks and allies; and (4) a large clade including wigeons, pintails, mallards, and several teal lineages. An examination of the distributions of species in light of the phylogeny indicates relatively little biogeographic structure. Geographic origin for most internal branches is ambiguous using several reconstruction methods. We suggest that the high dispersal ability of birds (especially dabbling ducks) has important implications for recovery of branches using molecular systematics. Received 26 January 1998, accepted 27 January 1999. THE DISTRIBUTION OF DABBLING DUCKS (genus Anas) on all continents except Antarctica is unusual for a genus of birds. In addition, many taxa of dabbling ducks are isolated on oceanic islands (Lack 1970, Weller 1980). This pattern of geographic distribution suggests that members of this genus are capable of long-distance dispersal. Chesser and Zink (1994) suggest hat the generally high dispersal ability of birds resuits in different biogeographic patterns than those commonly observed in other organisms. This high dispersal ability may result in speciation being driven by dispersal and allopatric speciation rather than classical vicariance (Wiley 1988, Chesser and Zink 1994, Ronquist 1997). The widespread distribution of dabbling ducks suggests that dispersal-driven speciation has been common in this group of birds. To fully interpret this biogeographic pattern, it is important to place species distributions in a phylogenetic ontext. • Present address: Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA. E-mail: [email protected] 4 Present address: Department of Biology, Boston University, Boston, Massachusetts 02215, USA. Phylogenetic relationships of the dabbling ducks remain controversial despite intensive study (see Livezey 1991). Livezey (1991) recognized the tribe Anatini in which he included all of the dabbling ducks and many of the "perching ducks." He classified the genus Anas and a few other closely related genera (Amazonetta, Callonetta, Lophonetta, Speculanas, and Mareca) within the subtribe Anateae. Livezey's (1991) detailed cladistic analysis of morphological characters contained several unresolved nodes and differed from previous taxonomic work on this group. We sought to further investigate the systematic relationships among species of Anas and within Livezey's subtribe Anateae using other genera within Anatini as well as additional members of the subfamily Anatinae as outgroup taxa. Molecular characters, in the form of DNA sequences, have incredible potential to provide new characters for phylogenetic analysis (Avise 1994, Hillis et al. 1996). To reevaluate phylogenetic relationships in the dabbling ducks, we first determined DNA sequences for two mitochondrial protein-coding genes: 1,047 base pairs (bp) of the cytochrome-b (cyt b) gene and the complete (1,041 bp) NADH dehydrogenase