Unravelling the ecological radiation of the capuchinos: systematics of Dark-throated Seedeater Sporophila ruficollis and description of a new dark-collared form

ARETA JI; PAGANO LG; NORIEGA JI; ROESLER I

BULLETIN OF THE BRITISH ORNITHOLOGISTS4 CLUB

BOU

Año: 2011 vol. 131 p. 4 - 23

0007-1595

The diverse genus Sporophila has a complex systematic history. A newdark-collared form of Sporophila seedeater, herein described on the basis of threeadult males, resembles male S. ruficollis but has a dark nape and rufous back. Weinformally name the new form ‘caraguata’ for its preferred habitat. We testedfour hypotheses regarding the systematic situation of the ‘caraguata’ form: validspecies, hybrid S. ruficollis × S. cinnamomea, colour morph of S. cinnamomea, andcolour morph of S. ruficollis. Vocally and ecologically, the ‘caraguata’ form cannotbe 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 andcannot be discarded. Sporophila ruficollis differs in preferred habitat, plumageand vocalisations from the rest of the capuchinos, and must be considered avalid species. The pattern of morphological variation exhibited by dark-throatedand grey-backed S. ruficollis and dark-collared and rufous-backed ‘caraguata’ isrepeated in the white-throated and grey-backed Marsh Seedeater S. palustris andwhite-collared and rufous-backed Entre Ríos Seedeater S. zelichi; moreover, themembers of each pair are indistinguishable ecologically and vocally. The ‘fuzzy’species borders and complicated taxonomy of the ruficollis group could stemfrom an ongoing evolutionary radiation in the capuchinos. This radiation hasapparently proceeded with little genetic divergence, simple changes in colour ofmale plumage, virtually no differences in females, and little morphological changein size and shape, but marked divergence in habitat use and voices of the involvedforms.