Proposal (897) to South American Classification Committee
A. Elevate Hylexetastes [p.] uniformis to species rank, and B. Establish English name for H. uniformis
Background: = From our SACC notes:
“The two species of Hylexetastes form a superspecies (Sibley & Monroe 1990); Marantz et al. (2003) suggested that vocal similarities and intermediate plumage of subspecies insignis suggests that they could be considered conspecific, as suspected by Zimmer (1934c). The subspecies uniformis was treated as a species separate from H. perrotii by Ridgely & Tudor (1994). Silva (1995) found no evidence for hybridization among various Hylexetastes taxa in areas where potentially parapatric and thus ranked all four taxa, including newly described brigidai (Silva et al. 1995), as species. Marantz et al. (2003), however, noted that voices of perrotii, uniformis, and brigidai are all quite similar.”
The HBW-BirdLife checklist and Piacentini et al. (2015) treat uniformis and brigidai as full species.
New information: Azuaje-Rodríguez et al. (2020) analyzed mitochondrial and nuclear sequences of 57 specimens representing all taxa in the genus. They found that taxa treated by us as a single species under H. perrotii are not sister because the subspecies from SE Amazonia, uniformis and brigidai, may be either more closely related to stresemanni (nuclear introns) or basal to a perrotii-stresemanni clade (mtDNA). There is no sign of gene flow among these three major groups, and they are reciprocally monophyletic. Azuaje-Rodríguez et al. also revealed that brigidai s nested within uniformis in both mtDNA and nuclear genealogies. Regarding species limits, they concluded that uniformis should be elevated to the species rank (including brigidai as a subspecies).
Fig. 1 of the paper: "From left to right: (a) Hylexetastes stresemanni stresemanni, (b) Hylexetastes stresemanni insignis, (c) Hylexetastes stresemanni undulatus, (d) Hylexetastes perrotii perrotii, (e) Hylexetastes perrotii uniformis, (f) Hylexetastes perrotii brigidai.
H. p. perrotii (note prominent moustachial stripe and light throat):
H.[p.] uniformis (note lack of patterns on head):
H. stresemanni (note throat pattern and black bars on underparts)
Discussion: The new information suggests that this genus is composed of three major lineages: perrotii, stresemanni, and uniformis. These three lineages show diagnostic plumage differences. In particular, uniformis can be easily distinguished from perrotii by its nearly uniform head pattern, lacking the whitish throat and, most notably, the whitish moustachial stripe of perrotii. Songs are reported to be similar across the genus, but a detailed analysis is lacking. For those of you prone to considering divergence time into consideration, the divergence between uniformis and perrotii (and stresemanni) was estimated to have occurred 6 million years ago by Azuaje-Rodríguez et al. (2020). This figure may be overestimated but Harvey et al. (2020) found the divergence between perrotii and stresemanni at 4 million years ago. So, definitely, these Hylexetastes lineages are not young.
Potential further subdivisions include the separation of brigidai from uniformis. However, brigidai is not fully supported as a separate lineage by the new genetic data: the sampled specimens formed a monophyletic group, but they were nested within uniformis. Although Silva et al. (1995) indicated a lack of intermediates or signs of gene flow between uniformis and brigidai, plumage differences are definitely more subtle, and they did not examine specimens from near the potential contact zone in the upper Xingu. There is also a big geographic gap in the genetic sample in the middle of the Xingu-Tocantins interfluvium. and two of the specimens from the southern sector of the interfluvium were found to be uniformis (Azuaje-Rodríguez et al. 2020, Fig. 2). If not wiped out by deforestation already, information from this potential contact zone would be crucial to clarify the status of brigidai.
English name: Because H. perrotii and H. uniformis are not sister lineages and have already been listed as different species with different English names, there is no need to create new names for this split. H. uniformis has been known as Uniform Woodcreeper (or Uniform Woodhewer) at least since Cory & Hellmayr (1925), where listed as a subspecies of H. perrotii, and where H. p. perrotii is listed as the Red-billed Woodhewer. Subsequent authors that treated H. uniformis as a different species, including several modern lists, always used Uniform Woodcreeper for this taxon and Red-billed Woodcreeper for nominate H. perrotii. Therefore, adopting this scheme would preserve stability and facilitate communication.
Part A. I recommend separating uniformis from perrotti as they are clearly phenotypically and genetically differentiated lineages and they are not even closest relatives. Hylexetastes would then be composed by three species in our classification.
Part B. I recommend adopting Uniform Woodcreeper for H. uniformis and retaining Red-billed Woodcreeper for H. perrotii.
Azuaje-Rodríguez, R. A., J. D. Weckstein, J. H. Dispoto, S. Patel, J. A. Cacioppo, J. M. Bates, S. M. Silva & A. Aleixo. 2020. Molecular systematics of the Amazonian endemic genus Hylexetastes (Aves: Dendrocolaptidae): taxonomic and conservation implications. Ibis 162(1):119-136.
Harvey, M.G., Bravo, G.A., Claramunt, S., Cuervo, A.M., Derryberry, G.E., Battilana, J., Seeholzer, G.F., McKay, J.S., O’Meara, B.C., Faircloth, B.C. and Edwards, S.V., 2020. The evolution of a tropical biodiversity hotspot. Science 370 (6522):1343-1348.
Piacentini, V.Q., Aleixo, A., Agne, C.E., Maurício, G.N., Pacheco, J.F., Bravo, G.A., Brito, G.R., Naka, L.N., Olmos, F., Posso, S. and Silveira, L.F., 2015. Annotated checklist of the birds of Brazil. Ornithology Research 23(2):91-298.
Santiago Claramunt, January 2021
Comments solicited from Curtis Marantz: “The proposal looks fine to me. I suspect they are reasonably good species, or at the very least, I am not sure any of the three Hylexetastes (H. stresemanni, H. perrotii, and H. uniformis) is any better or worse than any of the others. We treated H. uniformis as a subspecies mostly because there were no data to support its treatment as separate. Provided that there are now at least some data, I am okay with this one. I nevertheless suspect vocal data will show them to all have similar vocalizations, which is probably not ideal for taxa such as these. I suppose the other option would be to treat all Hylexetastes as one species, an option that can probably also be supported.
“I likewise agree with the treatment of H. brigidai as a subspecies of H. uniformis that shows plumage variation comparable with that of the members of the Dendrocolaptes certhia complex occurring in the same areas.”
Comments from Zimmer: “YES. As luck would have it, I just dealt with the writing of the species accounts of Hylexetastes for the forthcoming Birds of Brazil this past week, and had to wrestle with species-limits in the genus, so this topic is fresh in my mind. I had included a brief taxonomic note in the account of H. perrotii stating that species-limits were controversial, with anywhere from one to four species recognized, and had decided, even without the genetic data cited in this proposal, that neither the 4 species treatment followed by the Brazilian committee, nor our current 2-species treatment (which is also the one followed in HBW Volume 8) made the most sense from the standpoint of biogeography, nor did either of these treatments correspond to morphological or vocal differences/similarities based on my own field experience with each of the 4 primary units involved (I do not have field experience with nominate stresemanni, or insignis, but have examined specimens and photos of the latter). Although I would agree that nominate perrotii, stresemanni, undulatus, uniformis, and brigidai have similar songs (as noted by Marantz, et al. 2003), to my knowledge, no one has ever conducted a thorough vocal analysis, as Santiago notes in the Proposal. Prior to publication of HBW Volume 8, I spoke with Curtis (Marantz) about the species-limits that he was going to recognize for Hylexetastes in HBW, and shared my suspicion that the songs of perrotii might prove diagnosable from those of uniformis/brigidai, based upon my own field impressions. I believe that I also mentioned a particular agonistic call (one which I had noted only in response to audio playback) that was shared between brigidai and uniformis, that I had not heard from either stresemanni, undulatus, or perrotii. Nominate perrotii really stands out as phenotypically distinct, based upon not only the broad white moustachial stripe bordered by a broad, brown malar stripe, and the white median chin/throat, but also by virtue of its longer, heavier and more obviously red bill. By contrast, H. stresemanni has a relatively weak facial pattern (strongest in nominate, intermediate in insignis, and weakest in undulatus); but the pale chin and throat are distinctly dark-streaked; the breast is obviously pale-streaked; and the belly and crissum are conspicuously barred dusky (bold and wavy in S Bank undulatus). Compared to both perrotii and stresemanni, the SE Amazonian taxa uniformis and brigidai are notable mainly for their absence of distinctive markings – both taxa are remarkably plain-faced; the color of the upperparts and underparts are more nearly identical; the chin and throat are buffy and not white (like perrotii) nor conspicuously dark-streaked (as in the 3 subspecies of stresemanni); and the bill is shorter and duskier red. Setting vocal differences aside, in my experience, both uniformis and brigidai would be much more likely to be confused (in the field) with the sympatric subspecies concolor of Dendrocolaptes certhia than either would be with any other named taxon in the genus Hylexetastes. Now, with the addition of the genetic data of Azuaie-Rodríguez et al (2020), the status quo 2-species treatment would seem to be untenable, and supports recognition of the SE Amazonian clade (uniformis + brigidai) as a species distinct from both perrotii and stresemanni. Such a 3-species treatment fits nicely with the obvious phenotypic differences, as well as with my own anecdotal observations of vocal differences. The genetic data, as Santiago notes in the Proposal, are less strongly supportive of recognizing brigidai as specifically distinct from uniformis, and given collecting gaps and lack of knowledge from potential contact/intergrade zones in the Xingu-Tocantins interfluve, the subtle phenotypic differences, and my own anecdotal observations regarding vocal similarities (including a shared call type that may be otherwise unique within the genus), I think it most prudent to recognize brigidai as a subspecies of uniformis, at least until such time as we get broader sampling from contact zones, and/or until a thorough vocal analysis is conducted.”
The Proposal does not mention the issue of English names in the event that we adopt the recommended split, but I would note that Ridgley & Tudor (Volume II, Birds of South America), treated uniformis as distinct (this was prior to the formal description of brigidai), and gave it the English name of “Uniform Woodcreeper”, which would seem an appropriate extension of the specific epithet, and would be descriptive not only for nominate uniformis, but also for brigidai if included (as recommended) as a subspecies.
Comments from Robbins: “YES. After reading Santiago’s proposal and Kevin's comments, I vote yes for elevating Hylexetastes uniformis to species rank. Thanks to both for providing so much detail that makes this a straightforward decision.”
Comments from Piacentini: “Just for the record, CBRO has approved the lump of brigidai with uniformis for its forthcoming list, as a result of the recent paper.
“I have collected couple “brigidai” with MZUSP team at Fartura, in the border between Para and Mato Grosso states, near the Araguaia river. Both birds differ from each other as much as either differ from uniformis. Perhaps age has an important role here.”
Comments from Remsen: “YES. At this point the genetic data require removal of uniformis from H. perrotii (although if it were just mtDNA, all we would have is a gene tree, not necessarily a species tree).
“However, I am queasy about multiple species designations in the group. If they sound so similar, why not just treat all the parapatric taxa as a single species? How problematic are playback trials in woodcreepers? Just looking a current species limits in woodcreepers, without a doing a refresher course on the evidence for species limits in each, my perception is that there are major inconsistencies in what we know about voice and plumage in the group and how we have/haven’t applied that to species limits in so many cases, e.g. Xiphocolaptes, Dendrocolaptes, Xiphorhynchus spixii-elegans, X. ocellatus group, X. guttatus group, Sittasomus (insufficient published data so far, but maybe Peter Boesman could assemble enough if he hasn’t already), X. picus-kienerii, etc. etc. Marantz’s HBW chapter (2003) covered a lot of this complexity. What I’d like to see is a compilation and synthesis of what we know about the taxa that have contact zones to see if voice and plumage data show patterns of concordance with free gene flow or absence of it. Then, for better or worse but at least scientifically defensible, we could apply those results, if indeed there are patterns, to the taxa without contact zones, i.e. much like the Isler-Whitney system. If there are no patterns, then we’re stuck.”
“Although the sampling in Harvey et al. (2020) is weak within the genus, here’s that part of the tree:
“It also shows the paraphyly of H. perrotii. The Mato Grosso sample is H. p. uniformis by range, and the Pará sample I think is H. p. brigidai.
“Also, is brigidai a valid subspecies? Is it phenotypically diagnosable?”
Comments from Bonaccorso: “A. YES. Both mitochondrial and nuclear data support elevating Hylexetastes [p.] uniformis to species rank, with H. u. brigidai as a subspecies, at least for now.”
Comments from Stiles: “YES, including the recommended E-name of Uniform and the inclusion of brigidai as a subspecies, based on extensive commentary by Marantz and Piacentini. This brings this proposal to 6-0 for passing, but the E-name is less voted (3- or 4-0 YES).”
Comments from Pacheco: “YES. The data gathered by Santiago and those in Kevin's comments, allow a yes vote to treat Hylexetastes uniformis in the species level.”