Proposal (603.1) to South American Classification Committee

Split Sclerurus mexicanus into four species

Results of the voting on 603 (see below) were that 7 of 9 votes favored option B, i.e. a four-way split of S. mexicanus.

Therefore 603.1 becomes a YES/NO proposal on treating broadly defined S. mexicanus as four species:

B) Split mexicanus into four species. Recognize S. obscurior, and S. andinus as above, but tentatively treat peruvianus as a subspecies of its closest relative, S. macconnelli, pending a better understanding of their range boundaries, abutting ranges in southern Peru and Bolivia, and conclusive evidence of their evolutionary isolation, and phenotypic and behavioral distinctiveness (e.g., voices). Thus, this subproposal would remove S. mexicanus from the list and add three species. Sclerurus macconnelli would include the subspecies bahiae and peruvianus in addition to the nominate form.

(Van Remsen, Jan. 2015)

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Comments from Remsen: “NO. I am convinced that S. mexicanus consists of two or more species. The problem is that published data on this are minimal. See my original comments below. We need sonograms on the relevant taxa as well as full data on whether they are actually parapatric. I think Cuervo and Cooper are working on this, so we will see it eventually … thus I think it is unwise to proceed hastily.”

Comments from Pérez-Emán: NO – see my comments on the first version.”

Comments from Areta: “I would recommend a NO for the reasons clearly outlined by Van.”

Comments from Stiles: “I agree with Van that 3-4 species are hiding in S. mexicanus, but as work on voices and morphometrics is apparently proceeding, I am amenable to waiting a bit longer for publication of same and can change my vote to NO (for now). Certainly the birds that I have heard in Costa Rica sound different from anything I have heard in Colombia.”

Comments from Jaramillo: “YES – sticking to my original vote on this one.”

Comments from Pacheco: “NO. Changing my original vote. Waiting for more information (especially analysis of vocal repertoire of the implicated taxa) that allow better supported decision.”

Comments from Stotz: “NO. I previously voted for a 2 species solution.  Recognizing that there might be more species, I felt the case had not been sufficiently made for more than 2 species. So I voted to recognize obscurior as separate from mexicanus, but nothing more.  My question procedurally is what the consequence of a NO vote is.  Do we go to a single species recognized, just mexicanus, or does that lead to us recognizing mexicanus plus obscurior since all but 1 person voted for at least a 2 species treatment.  I would favor the result of a NO vote being a 2 species treatment, since I think everybody (except 1) voted for at least that.

“The original 603 proposal probably should have been structured as a set of contingent proposals.  First split mexicanus from obscurior, 2nd split obscurior into 3 species, third further split peruvianus from macconnelli.”

Response from Remsen: “In response to Doug’s query on the consequence of NO vote, S. mexicanus remains as a single species, for now. However, forthcoming publications on the group will likely make this only a temporary treatment.”

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Proposal (603) to South American Classification Committee

Split Sclerurus mexicanus into 2 to 5 species

Effect on SACC: Sclerurus mexicanus would be split into various species. One to three “mexicanus” subspecies from South America would be elevated to species rank. Because S. mexicanus sensu stricto has no confirmed records in Colombia (known as far as eastern Panama in Darién), it would be removed from the SACC list.

Background: Six species are currently recognized in the genus Sclerurus, but the relatively low diversity in this clade is probably a result of taxonomic bias from their relatively homogeneous drab coloration, size, and shape. Phylogeographic analyses showed an impressive genetic structure within all six Sclerurus leaftossers that suggested overlooked species diversity (d’Horta et al., 2013). Most differentiated populations within Sclerurus species are allopatric, with a few exceptions: S. scansor and S. mexicanus. Although a thorough revision of species limits in Sclerurus was beyond the scope of d’Horta et al. (2013) study, it demonstrated that S. mexicanus is not monophyletic as currently defined. Three major clades form a polytomy in the rufous-throated Sclerurus group: (1) S. mexicanus of Mexico and Central America, (2) S. rufigularis, and (3) S. mexicanus of South America. That is, the phylogenetic position of S. rufigularis with respect to the two large “mexicanus” clades was highly uncertain in their analyses using DNA sequences of mitochondrial genes and one nuclear locus.

Figure 1 - Phylogenetic relationships in the rufous-throated group of Sclerurus (based on d'Horta et al 2013). Vertical bars indicate species limits according to subproposals A, B and C. The black bar is for Sclerurus mexicanus.

Elevational parapatry of “S. mexicanus” lineages between lowland and Andean slopes, and their time of evolutionary isolation suggested that additional taxa should be elevated to species rank in South America. These elevational replacements involve at least: obscurior-andinus, and a pair of lineages of macconnelli-peruvianus.

From d’Horta et al (2013): “Along the continuum of humid forests from the Chocó lowlands to the slopes of the western Andes, two lineages seem to be segregated elevationally: S. obscurior [in red], and S. andinus found locally from about 1000 m (often up to 2000 m) [in blue]. The two lineages are potentially syntopic at an intermediate point of the elevational and ecological gradient, where no obvious physical barrier is in place… the lowland Chocó (i.e. S. obscurior) and the Andean foothill species (i.e. S. andinus)…[last] shared a common ancestor in the Early Pliocene, between 3.6 and 6.0 Ma”.

“In addition, S. macconnelli [in green] and S. peruvianus [in yellow]…are in close geographical proximity in southern Peru and Bolivia but seem to occupy different elevations along the cis-Andean foothills”.

Fig. 2 – Approximate geographic distribution of S. mexicanus taxa in South America, and point locality records of genetic samples from d’Horta et al. (2013) supplemented with new unpublished sequences. Stars indicate type localities.

Sclerurus mexicanus mexicanus (Sclater 1856). Suggested English name: Tawny-throated Leaftosser. Type locality: Córdoba, Veracruz, Mexico. This subspecies ranges from eastern Mexico to northern Nicaragua. Includes certus (Chubb 1919) from Guatemala, synonymized with mexicanus (Hellmayr, 1925, p. 248).

Sclerurus mexicanus pullus (Bangs 1902). Suggested English name: Isthmian Leaftosser. Type locality: Boquete, Panama. Occurs from Costa Rica through Darién in eastern Panama. There are no known verifiable Colombian records, hence not officially recorded in South America, but might extent to the Colombian Darién and Urabá regions. The subspecies anomalus (Bangs & Barbour 1922) described from Mt. Sapo, Panama, should be considered a junior synonym of pullus, not andinus (Peters 1951).

Sclerurus mexicanus obscurior (Hartert 1901). Suggested English name: Dusky Leaftosser (but this was used for pullus by Cory & Hellmayr). Type locality: Lita, Esmeraldas, Ecuador (ca. 600 m). Found in the Chocó lowlands of Ecuador and SW Colombia. This population consistently occurs at lower elevations than the adjacent andinus; however, it could extend locally to intermediate elevations (800-1200 m) where S. andinus occurs. The northern range boundary of obscurior is unclear. Specimens of S. obscurior are distinct from any other taxon by being decidedly darker overall, and having a more restricted rufous throat.

Sclerurus mexicanus andinus (Chapman 1914). Suggested English name: Andean Leaftosser. Type locality: Buenavista, above Villavicencio, Colombia, in the E slope of the Eastern Andes (ca. 1370 m). A subspecies of the humid Andean slopes in the three Andean ranges of Colombia, western Ecuador, the Venezuelan Andean foothills east to Lara, and Serranía de Perijá. It may range locally to the adjacent lowlands in NW Colombia and the Magdalena Valley. Hellmayr (1925, p. 249) included birds from Frontino, La Frijolera and Valdivia (in the Andes of NW Colombia) with anomalus (see pullus above), but Griscom (1932) and then Zimmer (1934) and Peters (1951) synonymized anomalus with andinus leading to the confusing distribution of interspaced andinus and anomalus/pullus in Eastern Panama (see Zimmer 1934, p.18). However, phylogeographic results and comparisons of more recent specimens from Antioquia (NW Colombia), E Panama, and S. m. obscurior, indicate an affiliation of Antioquia specimens to andinus (also see Meyer de Schauensee 1950, p. 690), and that the Panamanian pullus specimens exhibit greater variation in coloration. The assignment to andinus of populations from the tepuis in southern Venezuela and Guyana is most probably an error. Specimens of andinus are generally paler than not only obscurior but also most pullus and peruvianus; they have a brighter rufous rump, and the rufous throat is more uniform than in peruvianus in which it often has a whitish tint (more white at base of feathers).

Sclerurus mexicanus macconnelli (Chubb 1919). Suggested English names: MacConnell’s (or McConnell’s?)/Amazonian/Long-billed/Guianan (used by Cory & Hellmayr) Leaftosser. Type locality: Ituribisci River, Guyana. This taxon comprises populations of the Guiana Shield and most of Amazonia, with the exception of the western portion at the base of the Andes. However, range boundaries in this taxon are poorly understood, particularly in Central Amazonia. D’Horta et al. (2013) found population structure within macconnelli (three subclades), one of these subclades might come into contact with peruvianus locally in southern Peru and northern Bolivia.

Sclerurus mexicanus peruvianus (Chubb 1919). Suggested English name: Peruvian Leaftosser (as in Cory & Hellmayr). Type locality: Yurimaguas, Loreto, Peru. This taxon generally replaces macconnelli in NW Amazonia and at higher elevations in the Andean foothills of southern Peru and Bolivia. It also occurs in the lowlands and outlining ridges of NW Amazonia including both sides of the Napo/Amazon rivers in Ecuador and Colombia.

Sclerurus mexicanus bahiae (Chubb 1919). Suggested English name: Bahian Leaftosser. Type locality: Bahía, Brazil. This population, endemic of the Atlantic forest of eastern South America, is allopatric with respect to all other mexicanus subspecies. It was not sampled by d’Horta et al. (2013).

Sub-proposals: Although it is clear that Sclerurus mexicanus should be split, there is no single straightforward solution. We present three taxonomic alternatives considering the genetic results and current understanding of range distributions. Further studies may indicate that additional changes are necessary, such as moving pullus and bahiae to species rank, or describing additional taxa within the widespread Amazonian lineages (e.g., within peruvianus and macconnelli). See Fig. 1 above.

A) Split mexicanus into five species following d’Horta et al. (2013). This would result in the recognition of S. mexicanus (with two subspecies: mexicanus and pullus), S. obscurior, S. andinus; S. macconnelli (with two subspecies: macconnelli and bahiae); and S. peruvianus. If adopted, this proposal would remove S. mexicanus from the list and add four other species.

B) Split mexicanus into four species. Recognize S. obscurior, and S. andinus as above, but tentatively treat peruvianus as a subspecies of its closest relative, S. macconnelli, pending a better understanding of their range boundaries, abutting ranges in southern Peru and Bolivia, and conclusive evidence of their evolutionary isolation, and phenotypic and behavioral distinctiveness (e.g., voices). Thus, this subproposal would remove S. mexicanus from the list and add three species. Sclerurus macconnelli would include the subspecies bahiae and peruvianus in addition to the nominate form.

C) Split mexicanus into two species. Recognize S. obscurior, as a widespread, polytypic South American Sclerurus (the name obscurior has priority). This conservative scheme is the minimum change due on the basis of the paraphyly with S. rufigularis.

Recommendation: Although adopting sub-proposal C is a straightforward decision, various lines of evidence indicate multiple species-level taxa within the South American mexicanus group. Pending more information on the geographic distribution of peruvianus and macconnelli, we would recommend a vote for proposal B, which put both in the same species. We are convinced that obscurior and andinus are distinct lineages that merit species rank based on the data summarized herein and unpublished vocal analysis (J. Cooper in prep.). Transferring obscurior (Hartert 1901) and andinus (Chapman 1914) to species rank will not cause nomenclatural instability from future decisions regarding peruvianus, macconnelli or bahiae because the latter were named thereafter by Charles Chubb (1919).

Literature cited

d’Horta, F. M., A. M. Cuervo, C. C. Ribas, R. T. Brumfield & C. Y. Miyaki. 2013. Phylogeny and comparative phylogeography of Sclerurus (Aves: Furnariidae) reveal constant and cryptic diversification in an old radiation of rain forest understory specialists. Journal of Biogeography 40:37-49. PDF

Other references in the SACC bibliography.

Jacob C. Cooper and Andrés Cuervo

November 2013

Note from Remsen: Vote for A, B. or C, and the winner will be presented as a Yes/No proposal unless one of the three gets 7 or more votes on this round. We will deal with English names in a separate proposal.

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Comments from Stiles: “YES to proposal B; more data are required to justify proposal C, and proposal A clearly is oversimplified.”

Comments from Zimmer: “YES for Sub-Proposal B. As noted in the proposal, a two-way split of Central American mexicanus from all of the populations in South America is the minimum change dictated by the genetic data (Sub-Proposal C). This is too simplistic, and doesn’t reflect real differences in vocalizations and morphology within the various South American “subspecies”. At the same time, I don’t think we know enough about observed vocal differences or similarities, or the nature of potential contact zones between taxa (peruvianus and macconnelli) in Amazonia and the Guianan shield, or about possible geographic structure within those taxa, to justify further splitting (Sub-Proposal A) within those regions. It is tempting to view the isolation of bahiae as evidence for species-level recognition (from the macconnelli group), but, off the top of my head (without having actually sat down and compared recordings), the vocalizations of bahiae strike me as pretty similar to those of macconnelli from the southeastern part of the Basin. Regardless, I think the situation in the lowlands and foothills east of the Andes to the Atlantic Forest is complex enough as to require a thorough analysis, with, minimally, robust vocal samples spanning the ranges of all named taxa, before we attempt to resolve these relationships further than the treatment advocated in Sub-Proposal B.”

Comments from Pacheco: “[YES to proposal B] O recorte em quatro espécies, em minha opinião, é o mais apropriado em vista dos resultados da filogeografia disponível. Concordo com Kevin e suponho, igualmente, que novos estudos possam suportar mais desmembramentos. “

Comments from Robbins: “Clearly, multiple species are presently included under mexicanus. Until there is more information, proposal B seems the best course of action. So, a yes for proposal B.”

Comments from Remsen: “YES to proposal C. Although I agree with the sentiments of Kevin and others concerning the likelihood that at least 4 species are involved, these are weakly justified in terms of what is published, not only in terms of a minimal analysis of vocalizations but also even in terms of establishing the parapatry of the taxa. I think we should maintain rigorous standards in terms of requiring publication of critical data rather than lapsing into citing what are currently only slightly better than anecdotal information. What is now needed is a publication that documents parapatry using specific, mapped localities, not general range maps. What is also needed are some sonograms.”

Comments from Jaramillo: “Yes on B – I think that currently there is enough information to warrant a change up to this level, and I will not be surprised if further splits come in the future. Like in the related Miners (Geositta), I think there is a great number of cryptic species awaiting analysis.”

Comments from Stotz: “YES to Proposal C (two species split).  Likely that we will eventually split more species off, but I am not comfortable yet with more than the two species split.”

Comments from Pérez-Emán: “NO. This is an interesting proposal aiming to split Sclerurus mexicanus in different ways, from two up to five species. I think the phylogenetic hypothesis, together with information on plumage, distribution and vocal characters all suggest there is a higher diversity in this taxon than previously recognized. However, as Van has pointed out, there are no formal analyses on these variables to help selecting the potential alternatives delineated here in this proposal. I will go a step beyond and point out that the basis of the proposal is the paraphyly of S. mexicanus, a pattern that is not really shown in d’Horta et al (2013). Results of this study didn’t resolve the phylogenetic relationship between S. mexicanus y S. rufigularis, which were grouped together into a polytomy. This polytomy could disappear (or not) with more data showing that S. mexicanus is a monophyletic taxon. Monophyly cannot be discarded with present data. As such, splitting mexicanus into mexicanus and obscurior still needs support from morphological, ecological, distribution and vocal characters. Until such data are available, and with the idea to be consistent with our previous proposals, we will be able to make taxonomic decisions.

Comments from Areta: “I recommend YES to sub-proposal C. I agree with others in that multiple splits might be justified in the obscurior group, but until distribution patterns have been clarified and vocalizations have been shown to differ, I am reluctant to split species based just on branching patterns and levels of genetic divergence. Kevin's impressions on the lack of vocal distinction between the widely allopatric bahiae and macconelli make me wonder how much vocally distinctive other taxa in the complex are.

“This being said, I see that several proposals of species-level taxonomic changes are based on papers that are focused mostly on phylogenetic relationships, which per se do not necessarily provide definite evidence on the biological species status of the taxa. These phylogenetic works are complicated to discuss and assess because of the lack of biologically relevant information in them.”