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.
Photos:
H. p. perrotii (note prominent
moustachial stripe and light throat):
https://macaulaylibrary.org/asset/111141401#_ga=2.64124015.1933494220.1611929127-73344533.1611929127
H.[p.] uniformis (note lack
of patterns on head):
https://macaulaylibrary.org/asset/240090881#_ga=2.173595619.1933494220.1611929127-73344533.1611929127 and H.[p] brigidai
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.
Recommendation:
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.
New References:
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.”