Proposal (1028) to South American Classification Committee

Treat Synallaxis cinerea as conspecific with S. ruficapilla

The Synallaxis ruficapilla complex currently includes three species taxa: the Rufous-capped Spinetail (S. ruficapilla), Bahia Spinetail (S. cinerea), and Pinto’s Spinetail (S. infuscata). Also part of the complex is a geographically isolated population in the Brazilian state of Mato Grosso, often cited as a possibly undescribed taxon (Whitney and Cohn-Haft 2013, Batalha-Filho et al. 2013) but which may merely represent a range extension of ruficapilla. For a more in-depth overview of the complex, the reader is referred to the work of Stopiglia et al. (2013).

Phenotype

Stopiglia et al. (2013) examined geographic variation in plumage, morphometrics, and vocalizations. They found that only two populations in the complex are phenotypically diagnosable: one corresponding to infuscata and the other comprising the rest of the complex.

Genotype

Genetic research identified five mitochondrial lineages within the complex: one corresponding to infuscata, one to cinerea, one to the Mato Grosso population, and two lineages within ruficapilla (Batalha-Filho et al. 2013, 2019). All have very shallow nuclear divergence (Batalha-Filho et al. 2013, 2019; Harvey et al. 2020).

Recently, Batalha-Filho et al. (2019) analyzed two mitochondrial genes, two autosomal nuclear introns, and three Z-linked genes from many individuals of cinerea and ruficapilla. They discovered a wide hybrid zone between the two near the Jequitinhonha River. One Z-linked locus showed a narrow cline (~ 28 km), while all other loci showed wide clines (~ 179–529 km).

In summary, all taxa, including those that are phenotypically indistinguishable, are diagnosable units with respect to mtDNA. Additionally, there are other populations with equivalent levels of mtDNA divergence that are unnamed within the complex, namely the Mato Grosso population and one population within ruficapilla. The narrow cline for one Z-linked locus suggests some selection on the hybrid zone between cinerea and ruficapilla, although there is extensive gene flow on the rest of the genome.

How many taxa?

The S. ruficapilla complex presents a challenging situation for classification. The geographic phenotypic variation in the S. ruficapilla complex is similar to that of several other bird species complexes along the Atlantic rainforest, with a phenotypically diagnosable populations restricted to north of the São Francisco River and two somewhat differentiated, but not diagnosable, populations south of that river (e.g., Lima et al. 2024). In this broader context, S. cinerea seems to be another example of an avian taxon originally described from a small sample (Pacheco and Gonzaga 1995) that eventually proved undiagnosable with a greater sample (Stopiglia et al. 2013).

Given that cinerea and ruficapilla are phenotypically undistinguishable (Stopiglia et al. 2013), the only currently available basis for recognizing cinerea as a valid taxon (regardless of rank) is diagnosability on the basis of mtDNA and some Z-linked loci (Batalha-Filho et al. 2019). Regarding rank, extensive hybridization between cinerea and ruficapilla suggests that the current treatment of the two as separate biological species may be in error.

I recommend a YES vote to recognize as cinerea and ruficapilla as conspecific, based on the recent evidence of extensive gene flow and the lack of phenotypic diagnosability between the two.

References:

Batalha-Filho, H., M. Irestedt, J. Fjeldså, P. G. P. Ericson, L. F. Silveira, and C. Y. Miyaki (2013). Molecular systematics and evolution of the Synallaxis ruficapilla complex (Aves: Furnariidae) in the Atlantic Forest. Molecular Phylogenetics and Evolution 67:86–94.

Batalha-Filho, H., M. Maldonado-Coelho, and C. Y. Miyaki (2019). Historical climate changes and hybridization shaped the evolution of Atlantic Forest spinetails (Aves: Furnariidae). Heredity 123:675–693.

Harvey, M. G., G. A. Bravo, S. Claramunt, A. M. Cuervo, G. E. Derryberry, J. Battilana, G. F. Seeholzer, J. S. McKay, B. C. O’Meara, B. C. Faircloth, S. V Edwards, et al. (2020). The evolution of a tropical biodiversity hotspot. Science 370:1343–1348.

Lima, R. D., A. C. Fazza, M. Maldonado-Coelho, C. Y. Miyaki, and V. Q. Piacentini (2024). Taxonomic revision of the Scaled Antbird Drymophila squamata (Aves: Thamnophilidae) reveals a new and critically endangered taxon from northeastern Brazil. Zootaxa 5410:573–585.

Pacheco, J. F., and L. P. Gonzaga (1995). A new species of Synallaxis of the ruficapilla/infuscata complex from eastern Brazil (Passeriformes: Furnariidae). Ararajuba 3:3–11.

Stopiglia, R., M. A. Raposo, and D. M. Teixeira (2013). Taxonomy and geographic variation of the Synallaxis ruficapilla Vieillot, 1819 species-complex (Aves: Passeriformes: Furnariidae). Journal of Ornithology 154:191–207.

Whitney, B. M., and M. Cohn-Haft (2013). Fifteen new species of Amazonian birds. In Handbook of the birds of the world. Special volume: new species and global index (J. del Hoyo, A. Elliot, J. Sargatal and D. A. Christie, Editors). Lynx Edicions, pp. 225–239.

Rafael D. Lima, July 2024

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Comments from Claramunt: “YES. I studied the type series of cinerea at the AMNH myself, and I could not find any consistent difference with specimens of ruficapilla. The polymorphism in the song is intriguing, but it is not separating two taxonomic groups, as demonstrated by Stopiglia et al. (2012). My impression is that cinerea should not be recognized even at the subspecies level; it’s a full synonym of ruficapilla.”

Comments from Robbins: “YES for reasons outlined in the proposal.”

Comments from Stiles: “YES: the proposal seems clear and logical given the evidence adduced.”

Comments from Zimmer: “YES, for reasons nicely summarized in the Proposal. I do wonder as to whether Stopiglia et al. (2013) included specimens of the still-undescribed Mato Grosso birds in their study, and, if so, how many specimens of said population they examined. Hard for me to imagine that those birds are not diagnosable, or, that they represent merely a range extension of ruficapilla – if so, it would not represent just a significant range extension, but it would also mean that a bird that occupies Atlantic Forest, including montane forest, over most of its rather wide range, has a string of isolated populations occupying lowland Amazonian forest-edge between the Xingu basin and Alta Floresta.”

Comments from Josh Beck: “Despite not having had time to do an exhaustive analysis I spent quite some time listening to vocalizations on XC based upon my memory of the voice of these two taxa being distinctive. I am surprised by the fact that the vocalizations were not discussed in the proposal and haven’t been mentioned yet. They are instantly diagnosable by voice. My initial investigation in Xeno Canto of recordings along the species boundaries didn’t reveal any intermediate or out of place vocalizations, at least initially suggesting a clean boundary between the two species based on voice.”