Unravelling the ecological radiation of the capuchinos: systematics of Dark-throated Seedeater Sporophila

ARETA, JUAN I.; NORIEGA, JORGE I.; PAGANO, LUIS; ROESLER, IGNACIO

BULLETIN OF THE BRITISH ORNITHOLOGISTS4 CLUB

British Ornithologists' Club

Lugar: Londres; Año: 2011 vol. 131 p. 4 - 23

0007-1595

The diverse genus Sporophila has a complex systematic history. A new dark-collared form of Sporophila seedeater, herein described on the basis of three adult males, resembles male S. ruficollis but has a dark nape and rufous back. We informally name the new form ?caraguata? for its preferred habitat. We tested four hypotheses regarding the systematic situation of the ?caraguata? form: valid species, hybrid S. ruficollis × S. cinnamomea, colour morph of S. cinnamomea, and colour morph of S. ruficollis. Vocally and ecologically, the ?caraguata? form cannot be diagnosed from S. ruficollis. This evidence strongly suggests that S. ?caraguata´is a colour morph of S. ruficollis, although a hybrid origin is hard to assess and cannot be discarded. Sporophila ruficollis differs in preferred habitat, plumage and vocalisations from the rest of the capuchinos, and must be considered a valid species. The pattern of morphological variation exhibited by dark-throated and grey-backed S. ruficollis and dark-collared and rufous-backed ?caraguata? is repeated in the white-throated and grey-backed Marsh Seedeater S. palustris and white-collared and rufous-backed Entre Ríos Seedeater S. zelichi; moreover, the members of each pair are indistinguishable ecologically and vocally. The ?fuzzy? species borders and complicated taxonomy of the ruficollis group could stem from an ongoing evolutionary radiation in the capuchinos. This radiation has apparently proceeded with little genetic divergence, simple changes in colour of male plumage, virtually no differences in females, and little morphological change in size and shape, but marked divergence in habitat use and voices of the involved forms.