Proposal (751.1) to South American Classification Committee
Revise species limits in Polioptila guianensis complex
This proposal supersedes SACC proposal 751.0 based on new information from Smith et al (2018). Van and I agree with Stiles’ comment on proposal 751.0 that it might be best to reset the voting here. The earlier version and associated comments are included below the revised version, 751.1
SACC currently recognizes three species in the Polioptila guianensis complex (P. guianensis, P. schistaceigula, and P. clementsi). In SACC’s current arrangement, P. guianensis is polytypic, with three subspecies in addition to the nominate (paraensis, facilis, and attenboroughi). These taxa have ranges as follows:
· P. guianensis guianensis: Guiana shield south to Manaus
· P. schistaceigula: Trans-Andes including southern Mesoamerica.
· paraensis: South of the Amazon and east of the Madeira
· facilis: North of the Amazon and west of the lower Rio Negro; both banks of the upper Rio Negro
· P. clementsi: Lower Nanay Basin near Iquitos, Peru.
· attenboroughi: South of the Amazon and west of the Madeira
In proposal , SACC voted to recognize P. clementsi at the species level on the basis of its distinctive loudsong as well as minor plumage differences from the other members of the complex (Whitney and Alvarez 2005). In proposal , SACC voted not follow Whitney and Alvarez’s (2005) recommendation to split paraensis and facilis from guianensis. In proposal , SACC voted not to recognize attenboroughi (Whittaker et al 2013) at the species level, but some committee members expressed interest in an expanded proposal with separate opportunities to consider the status of paraensis and facilis. At the time, attenboroughi was assumed to be sister to paraensis based on similarities noted in the description of attenboroughi (Whittaker et al 2013).
Smith et al (2018) published a molecular phylogeny for all of Polioptila. This proposal focuses narrowly on the P. guianensis complex (including schistaceigula). A narrow focus is appropriate because the complex is monophyletic, and all possible changes fall strictly under the purview of SACC (provided that SACC does not choose to lump schistaceigula). Moreover, this focus is timely given HBW’s decision to lump clementsi with guianensis.
Smith et al (2018) provided two main products. The first is a gene tree for the mitochondrial ND2 gene that includes all relevant taxa (sample sizes 4 guianensis; 2 schistaceigula; 1 clementsi; 2 attenboroughi; 1 facilis; 1 paraensis). The second is a phylogeny using combined nuclear and mitochondrial markers (ND2 and six nuclear markers) that includes all taxa except for facilis. Three results are of particular importance for the present proposal. Of course, molecular phylogenies are not the be-all end-all of species delineation in weakly diverged complexes).
1) In the mitochondrial gene tree, Polioptila guianensis (sensu stricto) is basal to a clade containing P. schistaceigula and the remainder of the complex. This is surprising based on phenotypic characters; Whitney and Alvarez (2005) strongly suspected that the cis-Andean portion of the complex was monophyletic. However, the molecular data presented by Whittaker et al (2014) already suggested this arrangement. The combined nuclear/mitochondrial tree of Smith et al (2018) recovers the same topology, but with lower statistical confidence regarding the branching order of guianensis and schistaceigula. In both phylogenies, clementsi is unambiguously nested inside SACC’s concept of guianensis sensu lato.
2) Relationships between Polioptila attenboroughi, clementsi, and paraensis are poorly resolved. The weakest evidence for speciation/divergence is between clementsi and attenboroughi.
3) The position of facilis is not well resolved. The mitochondrial gene tree places it sister to paraensis, but with low statistical support.
Part A: lump the entire complex
A1 Lump guianensis and clementsi into an expanded Polioptila schistaceigula.
I recommend a NO vote.
A2 Lump clementsi into Polioptila guianensis while maintaining schistaceigula as distinct.
I recommend a NO vote.
If you voted YES on either A1 or A2, congratulations—you’re done! If not…
Part B: split the paraensis group from guianensis
B Split paraensis, including facilis and attenboroughi, from guianensis.
I recommend a YES vote. P. guianensis is not particularly close to the remainder of the complex. Note that facilis and guianensis presumably come into contact (or nearly so) somewhere east of the upper Rio Negro.
Part C: where to allocate attenboroughi and clementsi
C1 Treat attenboroughi as a subspecies of clementsi
I recommend a NO vote. The models used by Smith et al (2018) to delimit species were agnostic about whether attenboroughi and clementsi should be lumped or split. But this is a situation where phenotypic characters are informative. In fact, clementsi has perhaps the most distinctive loudsong in the complex, and there is no indication that attenboroughi ever gives a similar song. Neither Whitney and Alvarez (2005) nor Whittaker et al (2013) suspected a sister relationship between attenboroughi and clementsi.
C2 Treat attenboroughi as a subspecies of paraensis.
I weakly recommend a NO vote, for the reasons outlined by Zimmer in comments on proposals 751 and 619.
C3 Treat attenboroughi as a valid species. Proposed English name: Inambari Gnatcatcher, conforming to the original description, IOC, and eBird subspecies groups.
I weakly recommend a YES vote here. A YES on this question was the consensus of six out of seven committee members who voted on 751. It seems to me that the results of Smith et al (2018) only strengthen this viewpoint. The phenotypic characters separating attenboroughi from clementsi are substantial, and we now know that attenboroughi is perhaps as closely related to clementsi as it is to paraensis.
C4 Lump clementsi with paraensis
I recommend a NO vote.
Part D: what to do with facilis
Prior to the publication of Smith et al (2018), a lack of action on facilis would presumably have resulted in treating facilis as conspecific with guianensis. In light of Smith et al (2018), facilis would be treated as conspecific with paraensis, attenboroughi, or clementsi. Of these, clementsi is geographically proximate to facilis, while paraensis was recovered as the mitochondrial genetic sister to facilis (but with very low support).
I see no reason to lump facilis with clementsi or attenboroughi. Furthermore, lumping facilis with either clementsi or attenboroughi could introduce nomenclatural instability, since facilis would have priority. Therefore, I see only three realistic options:
D1 Treat facilis as a valid species. Proposed English name: Rio Negro Gnatcatcher, conforming to IOC and eBird subspecies groups.
I have no recommendation. Note that in comments on proposal 751, Stotz mentioned the distinctive irides of facilis—an interesting observation that I have not seen mentioned elsewhere.
D2 Treat facilis as a subspecies of paraensis.
I have no recommendation.
D3 Punt on the question: don’t make any decision about facilis for now.
I have no recommendation. In some ways this seems like the safest action given the limited data available. However, eBird and others will need to put facilis somewhere, and perhaps giving even a tentative recommendation would be better than no recommendation at all.
Part E: English names
To facilitate the implementation of this proposal, I recommend following the names that are already in use by IOC and eBird subspecies groups for any split taxa:
E1 If any of the following taxa are elevated to species status, adopt the following English names:
Inambari Gnatcatcher for attenboroughi (per Whittaker’s description)
Rio Negro Gnatcatcher for facilis
Para Gnatcatcher for paraensis
E2: dealing with a possible paraensis + facilis
Voting on proposal 751 was headed in the direction of recognizing paraensis but not facilis. The only data we have available for facilis (the mitochondrial gene tree) suggest without strong support that it might be best to treat it as a subspecies of paraensis. In case SACC reaches that conclusion, I think it’s worth considering possible English names for paraensis + facilis. I am not aware of good phenotypic or biogeographic characters to unite these taxa. Perhaps committee members have additional, better suggestions.
If SACC creates a polytypic paraensis with subspecies facilis:
E2.A: Use “Para Gnatcatcher” for paraensis + facilis
Pros: “Para Gnatcatcher” honors the type locality and is already in use.
Cons: Because “Para Gnatcatcher” is already in use, it is already understood to refer to the circumscribed taxonomic concept of paraensis sensu stricto, and it may well be used this way again in the future if new information results in the splitting of facilis. Moreover, facilis doesn’t occur anywhere near Para, whereas nominate guianensis does occur (probably extensively) in Para.
E2.B: Use “Klages’s Gnatcatcher” for paraensis + facilis
Pros: Honors the collector of paraensis. Furthermore, the only other Amazonian bird named for Klages (both in English and Latin) is Myrmotherula klagesi, with a distribution centered on the Rio Negro. Thus, the name “Klages’s Gnatcatcher” has some tenuous power to unite paraensis and facilis.
Cons: The above reasoning is so tenuous as to be absurd.
Indicate preference as A or B.
Smith, BT, RW Bryson, WM Mauck III, J Chaves, MB Robbins, A Aleixo & J Klicka. 2018. Species delimitation and biogeography of the gnatcatchers and gnatwrens (Aves: Polioptilidae). Molecular Phylogenetics and Evolution 126:45-57
Whitney, BM & 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 117:113-127.
Whittaker, A, A Aleixo, BM Whitney, BT Smith & J Klicka. 2013. A distinctive new species of gnatcatcher in the Polioptila guianensis complex (Aves: Polioptilidae) from western Amazonian Brazil. In J. del Hoyo, A. Elliott & D. Christie (eds.) Handbook of the Birds of the World, Special Volume: New Species and Global Index. Barcelona: Lynx Edicions 301-305.
Proposal (751.0) to South American Classification Committee
Revise species limits in Polioptila guianensis complex
There are five diagnosable forms within the Polioptila guianensis complex: the nominate guianensis [the Guianas south to the Amazon at Manaus], facilis [both banks of the upper río Negro], paraensis [south of the Amazon and east of the Madeira], attenboroughi [south of the Amazon and west of the Madeira], and clementsi [lower Nanay basin near Iquitos, Peru]. SACC currently recognizes two species: guianensis and clementsi. Morphology and voice suggest that attenboroughi is closest to paraensis (Whittaker et al 2013), and the names facilis and paraensis are both older than clementsi. Thus, it is safe to assume that the current SACC treatment views all taxa except clementsi as subspecies of guianensis sensu lato. This general treatment is the outcome of proposals 203 & 204, which provide a good summary of the situation based on Whitney and Alvarez (2005).
More recently, Whittaker et al (2013) presented new vocal analyses and genetic sequence data for guianensis and paraensis alongside their description of attenboroughi. Based on limited genetic sequence data (1041 bp of ND2, from 4, 1, and 2 individuals of guianensis, paraensis, and attenboroughi, respectively), the closely related paraensis and attenboroughi are somewhat distant from guianensis. Despite caveats related to the limited sample sizes divergence between (paraensis + attenboroughi) and guianensis appears to be larger than some other sister species pairs in the genus Polioptila, and there is a suggestion that P. guianensis sensu lato is not monophyletic. The vocal analyses show that attenboroughi is diagnosably distinct from other members of the complex (see proposal 619).
A less-discussed feature of Whittaker et al (2013) is their figure 2G, which shows a “multi-note call” from P. guianensis guianensis that
1) differs from the loudsong shown in Whitney & Alvarez, but
2) still generally resembles loudsongs within the complex.
Thus, Whittaker et al.’s interpretation that this vocalization is not a loudsong is critical to the notion that there are any diagnostic loudsong characters among this group whatsoever. For unclear reasons, this recording is not available in the supporting online material at www.hbw.com/supporting-information#polioptila-attenboroughi
Proposal provides a reasonable overview of the current situation. Some committee members expressed interest in an expanded version of proposal 619 that explicitly gives the committee the option to split facilis and paraensis from the nominate guianensis.
There is none. However, BirdLife/HBW has recently lumped clementsi with guianensis, which casts uncertainty over conservation efforts (including recent endangered species legislation in Peru) directed at the critically endangered clementsi. I do not advocate allowing conservation-related concerns to influence taxonomic decisions. However, the situation creates heightened applied interest in a formal decision by SACC to lump or continue to recognize clementsi (one way or the other).
The present proposal differs from proposal 619 in that it provides separate opportunities to consider the specific status of attenboroughi, paraensis, and facilis. It also asks SACC to reaffirm or reject species status for clementsi.
Split Polioptila paraensis from P. guianensis.
Recognize Polioptila facilis at the species level (distinct from both P. guianensis guianensis and P. (guianensis) paraensis).
Cease to recognize Polioptila clementsi as a species-level taxon.
Recognize Polioptila attenboroughi as a species-level taxon.
--If A passes, a NO vote on B would be agnostic about which form facilis belongs with. Because paraensis and guianensis both have priority over facilis, this is not destabilizing.
--Likewise, if A or B passes, a yes vote on C would be agnostic about which form clementsi should be lumped with. This poses no nomenclatural issues, as the other names have priority over clementsi. (This would otherwise be a nontrivial issue; witness the population of Platyrinchus saturatus that occurs sympatrically on white sands with Polioptila clementsi. It is vocally allied to birds from south of the Amazon, not birds from the Guianas!)
--Finally, if A or B passes, or C does not pass, a NO vote on D would be agnostic about which form attenboroughi should be lumped with (presumably paraensis).
B: no recommendation
D: no recommendation
Explanation of recommendations:
A: Data (limited by low sample sizes) suggest that (paraensis + attenboroughi) is not particularly close to nominate guianensis. In fact, (paraensis + attenboroughi) is apparently closer to schistaceigula than to guianensis. At present, the data are highly suggestive and sufficient to tip the scales to a YES vote, in my opinion.
B: If A does not pass, then neither should B (the arguments against passage are the same, and the arguments for passage are weaker due to the lack of genetic data). But I think A should pass. In that case, we have little data to determine whether facilis is closer to guianensis or paraensis, or whether it is conspecific with either taxon. As explained in the note above, it would not be destabilizing to hold off on making a decision about facilis. In that respect, it is fortunate that we have genetic data from paraensis and not facilis, rather than the other way around.
C: If A passes (as I think it should), then I recommend that clementsi should be maintained as a distinct species. To my ear, the song of clementsi is the most distinctive in the complex (provided that the “multi-note call” of Whittaker et al.’s Figure 2G is not homologous to the loudsong of clementsi). The tiny range and absurd degree of apparent habitat specialization despite extensive poor-soil habitats contiguous with the known range (observations of myself, Pepe Alvarez, Juan Diaz, and Percy Saboya) are unique within the complex. If paraensis is specifically distinct from the nominate, why not clementsi too?
If A does not pass, then I am agnostic about C. The information presented in Whitney and Alvarez (2005) was enough to convince the committee in proposal 203, and I don’t think subsequent information has changed anything.
D: As the committee recently expressed in comments on proposal 619, this is a difficult case without firm grounds for deciding. Some committee members suggested that they might vote to recognize attenboroughi in the context of a proposal that also allows for the splitting of paraensis from the nominate. So, here’s the proposal.
Jacob Socolar, April 2017
Comments from Zimmer: “I had a lot to say about this interesting case when evaluating previous proposals, and my current thinking hasn’t changed much from when we dealt with Proposal 619. I recycle my comments from 619 here, and will follow with some additional points specifically pertinent to the current proposal:
“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.”
“I think that the genetic data suggesting large differences between North bank guianensis and South bank paraensis/attenboroughi are too much to ignore, and, that at a minimum, we need to recognize at least 2 species (guianensis and paraensis). Again, I am basing this mostly on the genetic data, because I remain less than impressed by any plumage or vocal differences between these two taxa. The vocal analysis in Whittaker et al 2013, along with differences in saturation of plumage, suggests to me that attenboroughi is a valid taxon. The question then becomes one of “species or subspecies?” I could easily go either way on this question, except that recognizing attenboroughi as a species does fit with a pretty common biogeographic pattern of species-replacement across the Madeira. The same logic applies to facilis, which is another taxon whose alleged distinctions from guianensis always have left me slightly underwhelmed. If we end up accepting facilis and attenboroughi on biogeographic grounds, then it makes little sense to demote clementsi in my opinion. I could easily be persuaded to recognize just 3 species: a North Bank guianensis +facilis; a South Bank paraensis + attenboroughi; and a white sand specialized clementsi, but it makes less sense on biogeographic grounds given that the taxon-replacements we are talking about are across some truly massive river barriers in the Negro and Madeira. So, with that in mind, my votes are:
“YES” on A, B & D, and “NO” on C.”
Comments from Stiles: "A difficult proposal to judge, given the small simple sizes presented and the lack of data (especially more detailed vocal analyses) for some points; hence, my recommendations are tentative here.
“A. YES- at the least, the evidence now available supports the earlier suggestion by Whitney & Alvarez, and shifts the burden of proof to those continuing to consider guianensis and paraensis conspecific.
“B. NO- still too little information for facilis to justify a split.
“C. NO- the evidence by which we recognized clementsi still seems valid to me. However, to my knowledge genetic data are lacking: the description of clementsi stated that genetic samples were collected, and were being exported to LSU: were these samples received and analyzed there? I cannot recall ever having seen anything published on these, if so. Also, it would be helpful to know the reasons for BLI/HBW’s lumping of clementsi with guianensis.
“D. YES. The evidence presented in the description does favor recognition of attenboroughi as a species.
Comments from Claramunt: “NO. It is impossible to split this complex without further information on: 1) geographic variation in plumage, vocalizations, and genetics, 2) establishing diagnosability (I have not seen a specimen-level analysis that demonstrates it); 3) determining affinities of facilis and clementsi within the complex (i.e. minimally, placing them in the mtDNA tree); 4) have a sense of whether song differences have something to do with reproductive isolation.
“That attenboroughi and paraensis cluster with schistaceigula instead with guianensis does suggest the presence of more than one linage but we need to know where to allocate facilis and clementsi. Variation within the complex does suggest more than one species but the possibility of a single species with geographic structured phenotypic variation has not been ruled out, in my opinion.”
Comments from Remsen: "I agree with Gary on the difficulties in judging the proposal, but the proposal was generated by the HBW decision to not recognize clementsi. Like Gary, my votes are tentative (and I understand Santiago’s view of all this). They are not, however, influenced by genetic distance data, which presumably reflect time-since-divergence at neutral loci and have nothing to do directly with speciation
“A. YES. Although the evidence is weak, like Gary, I think it tips the balance.
“B. NO. Insufficient data.
“C. NO. No additional evidence has been produced that counters current classification. Further, that clementsi fails to meet the “magic 7 points” of the BLI classification system is and indictment of that system, specifically its failure to account for phylogenetic differences among groups, and not a measure of taxonomic rank. The genus Polioptila is notoriously conservative phenotypically, so chances of species reaching species rank by a subjective scoring system of morphological characters are minimal. Vocally, clementsi is by all accounts distinctive, and that alone is sufficient for separate species treatment.
“D. YES, as per rationale in the proposal and Kevin’s excellent comments.”
Comments from Pacheco: "Taking the opportunity to revisit the case with this well-organized proposition, after reading especially comments from Kevin and Van, my votes are: YES on A & D, and NO on B & C”
Note from Jacob Socolar, 28 Feb. 18:
The following paper from Smith et al is highly relevant to SACC proposal 751.
It includes a phylogenetic hypothesis for all relevant taxa as well as a gene tree that includes facilis. I am currently in the field and unable to evaluate the paper thoroughly, but the paper contains a few key phylogenetic surprises, namely that attenboroughi is apparently closest to clementsi. Without an opportunity for deeper study, I don't profess to understand the models used to delimit species, but the paper asserts that these models support species status for all species in the complex except for the attenboroughi (which is sister to clementsi) and facilis (which is excluded due to missing data).
Because of the differences in song between clementsi and attenboroughi, I think it is reasonable to treat attenboroughi as a distinct species (surely the argument for treating it as distinct from clementsi is stronger than the previous argument for treating it as distinct from paraensis). If it is not treated as a species, it is unclear to me whether it is best placed with paraensis or with clementsi.
Additionally, this new paper has major implications for splitting other species complexes within Polioptila, clearly showing that a yardstick method against P. plumbea (for example) would not be appropriate (I think the committee already recognizes this).
Thus, I tentatively revise my recommendation to a YES on part D. I continue refraining from making a recommendation on part B, though I find the idea of a species consisting of paraensis + facilis to be somewhat biogeographically surprising.
Interestingly, the paper suggests that clementsi arrived at Iquitos from the southern Amazon, rather than from the Guianas. I alluded to this possibility in the original proposal 751, and note that it conforms to a biogeographic pattern shared by Platyrinchus saturatus and Deroptyus accipitrinus.
Comments from Stotz: “YES on A and B. NO on C. YES on D. I don’t have any vocal data to contribute on facilis, but I have seen and collected it. To me, it looks morphologically more distinctive than paraensis. The bird I collected had yellow irides. The paraensis I have collected had brown irides. Don't know what that means, but quite striking.”
Comments from Jaramillo: “Part A – YES. Part B – NO. Part C – NO. Part D – YES per Kevin’s influential comments.”
Additional comments from Stiles: “Here, we’ll probably need to digest the recent, most comprehensive phylogeny of the Polioptilidae before making any firm decisions: the polyphyly of several currently recognized species (plumbea in particular) are in line with Kevin’s comments. Both NACC and SACC could have considerable work to do on this one, so perhaps the best thing to do for no. 751 is table it for now?”