Portal de Periódicos da CAPES

A phylogenetic reassessment of the tadornine-anatine divergence (Aves: Anseriformes: Anatidae)

1996; Volume: 65; Issue: 1 Linguagem: Inglês

10.5962/p.215133

1943-6300

Bradley C. Livezey,

Morphological variations and asymmetry

Phylogenetic analysis of eight problematic genera of waterfowl {Stictonetta Plectropterus, Sarkidiornis, Hymenolaimus, Tachyeres, Merganetta, Malacorhynchus, and Salvadorina) and representatives of other tadornine genera and anatine tribes was undertaken using 114 morphological characters (39 skeletal, four tracheal, 1 1 natal, and 60 of the definitive integument) and a variety of weighting schemes, in an attempt to clarify relationships in the most poorly understood segment of the phylogeny of Anseriformes (Livezey, 1986<3).Under equal weighting of characters, 40 equally parsimonious trees were found that shared the following findings: (1) a sister-group relationship of Stictonetta to a clade comprising the Tadorninae and Anatinae; (2) a sister-relationship between Plectropterus and Sarkidiomis; (3) monophyly of the typical shelducks and sheldgeese (Tadorna, Cyanochen, Alopochen, Neochen, and Chloephaga); (4) monophyly of Hymenolaimus, Tachyeres, and Merganetta-, and (5) a sister-relationship between Salvadorina and Malacorhynchus.An analysis wherein skeletal characters were given twice the weight of other character groups resulted in four shortest trees which, in addition to the findings under equal weighting, indicated that: (1) Plectropterus + Sarkidiornis represent the sister-group of the typical shelducks and sheldgeese; (2) a sister-relationship between the clade comprising Hymenolaimus, Tachyeres, and Merganetta and the preceding clade, collectively constituting the "tadornine" clade; and (3) a sister-relationship between Malacorhynchus P Salvadorina and an "anatine" clade comprising the remaining tribes and subtribes (Cairineae, Nettapodeae, Anateae, Aythyini, Mergini, and Oxyurini).An analysis in which skeletal, tracheal, natal, and definitive characters were assigned weights of four, three, two, and one, respectively, produced identical results to the preceding weighting scheme.Successive weighting by rescaled consistency indices produced two shortest trees that resembled those found under the two preceding protocols except: (1) the Mergini were placed as the sister-group of the "tadornine" clade defined above; and (2) the Cairineae (Cairina, Pteronetta, and Aix) were placed as the sister-group to Plectropterus + Sarkidiornis.Based on the comparative strengths of hypothesized homologies of skeletal characters and assessments of topological support (including bootstrapping, decay indices, and near-shortest trees) for all weighting schemes, a conservative classification was based on the a priori weighting schemes favoring skeletal characters.Maps of selected ecomorphological attributes on this phylogenetic tree revealed several distinct evolutionary trends, but incompletely resolved relationships among these diverse genera and within suprageneric taxa limited inferences.Additional promising areas for anatomically based systematic study are identified, and the need for continued cladistic study of this poorly resolved but topologically critical segment of the phylogeny of Anseriformes is emphasized.