Proposal (619) to South American Classification Committee
Recognize newly described Polioptila attenboroughi and split Polioptila guianensis into three species
Effect on SACC: If adopted, this proposal would add a newly described species of Polioptila to the list and recognize two current subspecies of P. guianensis (paraensis and facilis) as species-level taxa.
Background: Based on several sight records and tape-recordings and three specimens collected of a member of the P. guianensis group west of the Rio Madeira, Whittaker et al. (2013) described a new species of Polioptila, P. attenboroughi, from the west bank of the Madeira and south of the Solimões rivers in the Inambari area of endemism (Silva et at. 2005) in Brazil. Analyzes of the tape-recordings and of the collected specimens indicated that this taxon is phenotypically and genetically distinct from other taxa in the P. guianensis complex.
Newly Published information:
Morphology. - Adult males (no female specimens are available) of the new taxon are readily distinguished from males of all remaining taxa in the P. guianensis complex by decisively darker plumbeous upperparts, chest and lower throat, in these respects approaching P. facilis and P. schistaceigula (Slate-throated Gnatcatcher) further differing from the former by a thin, broken, white eye ring (nearly absent in P. facilis), and from the latter by a significantly longer tail with white on the outer feathers, and lack of any white in the head. In comparison with recently described P. clementsi, it further differs by the greater extent of black basis on outer rectrices. From P. paraensis, with which the new taxon shares the tail pattern, differentiated only by a much darker slate color of the upperparts, throat, and chest (Whittaker et al. 2013).
Voice. - The loudsong of P. attenboroughi is most similar to that of P. paraensis in comprising an evenly paced series of notes at a nearly level frequency, but pace is significantly slower and note shape (and thus, auditory quality) is subtly different. Furthermore, P. attenboroughi possesses a distinctive "rasp" series delivered in the context of a complex song that is lacking, or perhaps only very rare, in P. paraensis but shared with P. schistaceigula (Fig. 2 in Whittaker et al. 2013).
Genetic divergence. - Separated from its sister-species, P. paraensis, by approximately 3.9% sequence divergence, and from the more distantly related P. schistaceigula and P. guianensis, respectively, by 14.3% and 13.6% sequence divergence in the mitochondrial gene NADH subunit 2 (Fig. 3 in Whittaker et al. 2013). The uncorrected p genetic distance between P. attenboroughi and P. paraensis (3.9%) is nearly identical to that reported for a pair of parapatric sister-species of Polioptila in North America (4% for P. californica and P. melanura), and also based on the same gene (Zink and Blackwell 1998).
Analysis/Recommendation: The fact that the phylogenies recovered P. attenboroughi and P. paraensis as reciprocally monophyletic taxa with strong statistical support (Fig. 2 in Whittaker et al. 2013), along with their morphological and vocal differentiation, supports their recognition as valid species-level taxa (De Queiroz 2007). The English name, Inambari Gnatcatcher, reference the center of endemism to which the new taxon is restricted. Also, the molecular phylogeny obtained by Whittaker et al. 2013 showed with strong support that the Polioptila guianensis complex is not monophyletic with respect to Polioptila schistaceigula from west of the Andes, reinforcing the treatment of other taxa currently regarded as subspecies in this complex (paraensis and facilis) as independent species, as supported by Whitney and Alvarez (2005).
De Queiroz, K. (2007). Species concepts and species delimitation. Systematic Biology 56 (6): 879-886.
Silva, J. M. C., S. B. Rylands, and G. A. B. Fonseca. (2005). The fate of the Amazonian areas of endemism. Conservation Biology 19: 689-694.
Whitney, B. M. and J. Alvarez A. (2005). A new species of gnatcatcher from white-sand forests of northern Amazonian Peru with revision of the Polioptila guianensis complex. Wilson Bulletin 117:113-210.
Whittaker, A.; Aleixo, A.; Whitney, B. M.; Smith, B. T., and Klicka, J. (2013) A distinctive new species of gnatcatcher in the Polioptila guianensis complex (Aves: Polioptilidae) from western Amazonian Brazil. In: J. del Hoyo, A. Elliott e D. Christie. (Org.). Handbook of the Birds of the World, Special Volume: New Species and Global Index. 1ed. Barcelona: Lynx Edicions, 301-305.
Zink, R. M. and R. C. Blackwell. (1998). Molecular systematics and biogeography of arid land gnatcatchers (genus Polioptila) and evidence supporting species status of the California Gnatcatcher (Polioptila californica). Molecular Phylogenetics and Evolution 9: 26-32.
Lincoln Carneiro and Alexandre Aleixo
Comments from Remsen: “NO, but based strictly on a technicality, namely the proposal is framed as if paraensis and facilis are treated as species, which SACC does not – see proposal So, we can’t elevate attenboroughi to species rank without also reconsidering the critical taxa in this group. Also, as noted in my comments on similar proposals, discussing “reciprocal monophyly” with such a small N of individuals is completely inappropriate. Further, comparative genetic distances are also an inappropriate way to evaluate species limits, especially when temperate-latitude taxa are compared to isolated tropical ones. That said, the vocal differences portrayed in the sonograms and described in the text, combined with the plumage differences, are consistent with species rank for taxa in this group, given that these differences are comparable to those between taxa treated as species in this genus, in which morphological divergence is slight. What we need is a comprehensive proposal on the group, i.e. a revised 204 combined with the current one.”.
Comments from Stiles: “NO. The evidence presented could be sufficient for recognizing attenboroughi, but whether as a subspecies or species is uncertain without more data from all forms of this gnatcatcher complex: in effect, in order to justify splitting all these forms as species requires more comprehensive data (morphometrics, voice, genetics) from all of them; also, the painting of attenboroughi fails to show the supposedly diagnostic difference in tail pattern; photos of representative specimens of all forms showing this (as well as other characters mentioned) should also be included.”
Comments from Nores: “NO, for the reasons given by Van and Gary. We can’t elevate attenboroughi to species rank without also reconsidering the critical taxa in this group. The evidence presented may be sufficient for recognizing attenboroughi, but whether as a subspecies or species is uncertain. Discussing “reciprocal monophyly” with such a small number of individuals is inappropriate.”
Comments from Zimmer: “YES, although with more than a little hesitation. I spearheaded the rejection of Proposal 204 (splitting guianensis into 3 species), largely on the grounds that I felt the sample sizes of audio recordings were tiny (and with virtually no geographic breadth) for nominate guianensis and facilis, and, because I felt that the described vocal differences between the three taxa were subtle relative to those between subspecies-pairs in the plumbea and dumicola complexes (and, because we are dealing with oscine passerines whose vocal repertoire is at least shaped by learning). The description of attenboroughi has the added advantage of genetic data (but see caveats by Van, Gary and Manuel in their comments on this proposal), revealing some pretty large sequence divergences between north-bank guianensis and the clade containing paraensis and attenboroughi. Also, Whittaker et al (2013) fleshes out the vocal comparison, at least for attenboroughi and paraensis, although it does little to make the case for guianensis and facilis beyond presenting the genetic data. I have seen and tape-recorded all four taxa (including attenboroughi), and I continue to be underwhelmed by the relatively subtle vocal differences among the 4 taxa in the guianensis complex, at least when these are placed in the context of vocal differences between populations of P. plumbea and P. dumicola that are still considered subspecies despite having dramatically different songs. As I stated in my remarks on Proposal 204, this may be less an indictment of recognizing attenboroughi and splitting guianensis than it is an argument for splitting up plumbea and dumicola, but it does mean that the yardstick approach cannot be used in making the present case. I think that the qualitative (= note shape and call structure) differences between attenboroughi and paraensis noted by Bret in his vocal analysis in Whittaker et al 2013 are likely more significant than the pace differences in the primary songs, especially given that the songs in these birds are learned. I am not bothered by the relatively minor plumage distinctions between the four taxa – plumage variation within the genus is highly conservative. [Just as an aside, Whittaker et al 2013 describe the plumage of attenboroughi as being very saturated, dark gray, “approaching schistaceigula”. This does not square with my experience with schistaceigula from Panama, which is nearly blackish-gray, and much darker than any of the attenboroughi that I’ve seen (6-8 individuals, including what appeared to be a family group of 4). It is possible that the schistaceigula at the western limit of their range are darker than the South American populations – if so, then schistaceigula may also exhibit some geographic structure in vocalizations, making everything in the complex more complicated than previously thought.] Anyway, I think that Whittaker et al 2013 makes a strong case for recognition of attenboroughi as a distinct taxon in the guianensis/schistaceigula complex – it should be recognized at some taxonomic level. I’m on the fence as to whether that level should be as a distinct species versus a subspecies of a polytypic guianensis, but biogeographic considerations and the genetic data suggest to me that treating each of the populations as separate species that are part of a superspecies is probably the correct course. So, again, a tepid YES.”
Comments from Robbins: “YES. Van makes the point that given how we haven’t recognized paraensis and facilis (I was on the fence on whether they should be recognized as a species) that we shouldn’t make a decision on the status of attenboroughi until we address the entire guianensis complex. As at least a couple of us pointed out in our evaluation of proposal 204, plumage morphology is so subtle and plastic in this family that in my opinion it has little utility. Moreover, having analyzed literally dozens of songs both within and across Polioptila taxa, I would submit that this character also has limited utility in defining species limits. Thus, given those limitations, I do consider the genetic data to be very important in assessing species limits. The fact that attenboroughi is so different from purported relatives leaves no doubt that at a minimum paraensis and attenboroughi together should be considered a distinct species from other taxa within guianensis. However, I would go one step further and now would support recognizing both paraensis and attenboroughi as species. Of course, if we take that path then I presume that we should treat clementsi and facilis as species.”
Comments from Pacheco: “YES. Considerando as ressalvas feitas pelo Van e a necessidade de se reavaliar os táxons adicionais do complexo, considero a ponderação de Kevin como justificável razão para optar por um SIM.”
Comments from Jaramillo: “YES – this is a tough one, marginal, yet the little information that is out there seems to be borderline positive to make some decisions. I see the point made by Van on structure of the proposal (it is not the best argument made there in my opinion, a bit messy and confusing), but I am following the thoughts by Mark Robbins. There are characters mentioned in the proposal that are perhaps not all that useful, but even with the small sample size and limitations the sequence divergence is large. Adding things up, primarily basing on sequence divergence, but adding in the morphology and song, I do think that this newly described species is a good one.”
Comments from Stotz: “YES I understand that this only makes sense if facilis and paraensis are split from guianensis, but I think they should be. If this were still in question, I might be a little more concerned about the niceties of doing a proper proposal for facilis and paraensis. I would encourage a new proposal to split all of these personally, although reading the comments makes it unclear to me that with the current data, enough of the committee would be convinced.”