Proposal (604) to South American Classification Committee
Merge Oryzoborus and Dolospingus into Sporophila
Effect on SACC: This proposal would merge the genera Oryzoborus and Dolospingus into a broadly defined Sporophila.
Background: The genera Sporophila, Oryzoborus, and Dolospingus comprise a group of small-bodied, thick-billed oscines that are widely distributed in open and semi-open habitats throughout the Neotropics (Meyer de Schauensee 1952; Ridgely and Tudor 2009). These genera appear together in all current classifications, such as Clements et al. (2013), who recognize 39 species within these genera. Based on similarities in nests, eggs, plumage sequences, and songs, authorities have long suspected that these genera are closely related (Olson 1981; Sick 1963; Stiles 1996). Recent molecular phylogenies have confirmed that Sporophila, Oryzoborus, and Dolospingus form a clade (Burns, Hackett, and Klein 2002; Lijtmaer et al. 2004; Robbins et al. 2005) that does not include any other thraupid genera (Barker et al. 2012); however, limited taxonomic sampling has restricted our ability to evaluate the reciprocal monophyly and taxonomic validity of these genera.
New information: Mason and Burns (2013) sampled 33 out of the 39 species currently recognized by Clements et al. (2013) in their study of phylogenetic relationships within this group, and included the type species: S. falcirostris Temminck 1820. Based on Bayesian and maximum likelihood inferences using the mitochondrial gene regions ND2 and cyt b, Mason and Burns (2013) found that Sporophila is paraphyletic as currently defined (Figure 1). More specifically, S. lineola is sister to the remaining taxa sampled; therefore, other species of Sporophila are more closely related to members of Oryzoborus and Dolospingus than they are to S. lineola. Mason and Burns (2013) also found that a constrained topology, wherein each genus was forced into monophyly, was decisively worse than an unconstrained topology (2ln Bayes Factor = 18.9). Moreover, many of the strongly supported nodes in Mason and Burns (2013) represent novel relationships that are not reflected in the current linear sequence of this group.
Analysis: Although the phylogeny from Mason and Burns (2013) is missing six taxa (S. americana, S. ardesiaca, S. bouvronides, S. frontalis, S. murallae, and S. nigrorufa) and relies solely on mtDNA, they found strong evidence that Oryzoborus and Dolospingus are embedded within Sporophila. Based on this finding, Mason and Burns (2013) suggested merging the genera Oryzoborus and Dolospingus into a broadly defined Sporophila, which has taxonomic priority over the other two genera (Cabanis 1844; Cabanis 1851; Elliot 1871). This revision has already been suggested by other studies that recovered similar topologies with fewer in-group taxa (Burns, Hackett, and Klein 2002; Lijtmaer et al. 2004; Olson 1981). Although some previous investigators have favored retaining these genera to recognize differences in morphology (Stiles 1996; Webster and Webster 1999), we note that bill size and shape, as well as body size, can be extremely labile in passerines (Remsen 2003). Furthermore, similar levels of bill diversity already exist in other granivorous oscine genera, such as Passerina (Klicka et al. 2001).
Figure 1: Maximum clade credibility tree of Neotropical seedeaters and seed-finches inferred using BEAST with posterior probabilities above each node and bootstrap support values below each node. The phylogeny is rooted with 21 species from 18 genera representing each of the major clades of tanagers.
Recommendation: We recommend a “YES” vote to merge Oryzoborus and Dolospingus into a broadly defined Sporophila.
Note: A separate proposal will follow for the linear sequence of species.
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Burns, K. J., S. J. Hackett, and N. K. Klein. 2002. Phylogenetic relationships and morphological diversity in Darwin’s finches and their relatives. Evolution 56: 1240–52.
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Nicholas A. Mason, November 2013
Comments from Stiles: “YES. I see no reasonable alternative although some nuclear DNA would be nice to substantiate the lumping of Oryzoborus and Dolospingus into Sporophila. However, the Galápagos finches also provide a good example of how bill morphology can be very plastic in relation to the seed sizes a taxon encounters, so I’m willing to forego my bill morphology-based defense of a separate Oryzoborus.”
Comments from Zimmer: “YES. The evidence seems pretty compelling, and bill morphology (the primary distinction between the three genera as currently recognized) is clearly a plastic evolutionary character among seed-eating birds. I do find it a little painful to sink Dolospingus, which somehow “feels” more different, but the genetic data say otherwise.”
Comments from Nores: “YES. Note: based on the molecular analysis of Lijtmaer et al., I proposed (proposal 264) the merger Oryzoborus into Sporophila, but the proposal did not pass.”
Comments from Pacheco: “YES. A filogenia de Mason & Burns encontrou fortes indícios que os dois gźneros estčo claramente embutidos dentro do que conhecemos por Sporophila, corroborando mais uma vez o encontrado em estudos independentes.”
Comments from Robbins: “YES, the mitochondrial data clearly indicate that Oryzoborus and Dolospingus should be subsumed within Sporophila.”
Comments from Stotz: “YES, weakly. I part of me wants to go the other way, retain Oryzoborus and split up Sporophila, with lineola, the little guys at the top, and the big complex at the bottom. So we’d have 4 genera. Problems with that are the topology might be unstable to the addition of the missing species or additional molecules, and I have no idea whether there are available names.”