Proposals (408-411) to South American Classification Committee

 

408. Change linear order of current Thryothorus wrens (II)

409. Recognize genus Pheugopedius (II)

410. Recognize genus Thryophilus (II)

411. Recognize genus Cantorchilus (II)

 

Summary: This proposal would result in a new genus name or names for the current SACC Thryothorus wrens.  In Proposal 219, all committee members were in favour of taking such a step, but there was no agreement on using Mann et al. (2006)'s three-genus approach for South American Thryothorus.  This decision should be reconsidered in light of vocal analysis by Mann et al. (2009).  However, if the three genus approach is again to be rejected, then SACC should either revert to Hellmayr's two genus treatment for S American Thryothorus or move them to other genera.  The current baseline remains as Thryothorus for all these species, which cannot be supported.

Discussion: In Proposal 219, in a close vote, SACC decided not to split S American Thryothorus into three new genera.  However, there was considerable support in the comments of dissenters for moving all South American Thryothorus to Pheugopedius.  The proposition that Thryothorus is not monophyletic has strong support from multiple studies, as discussed in Proposal 219 and further shown by Mann et al. (2006) and papers cited therein, with true Thryothorus occurring only outside the SACC region.

There was some scepticism over Proposal 219 given that Mann et al. (2006)'s diagnosis of the new genus Cantorchilus involved only molecular characters: "Currently, no known uniquely derived morphological characteristics diagnose the genus Cantorchilus, as defined here. Given current taxonomic and character sampling, the genus is diagnosable by 9 unreversed synapomorphies in cytochrome b (including: A150C, A156G, C297T, A876C, C903A, C924A, A948G, C960A and C1116A, where aNb refers to the ancestral state a and derived state b at position N), all at third codon positions, including 6 transitions and 3 transversions, one of which results in an amino acid replacement (I372M)."

Daniel Cadena (who voted in favour of adopting the three genera) in his comments on Proposal 219 noted "it appears to me that the songs of Thryophilus (rufalbus and nicefori, which I am familiar with) stand out as rather unique when compared to those of other "Thryothorus" I know."  This has now been borne out with analysis.  Mann et al. (2009), based on sampling of almost all relevant species, showed the three proposed genera to be diagnosable on the basis of duetting behaviour and also noted some behavioural differences (separation by forest strata) between members of different proposed new genera where they occur together.  For example, Thryophilus sensu stricto don't duet or duet in a very temporally uncoordinated fashion, whereas Cantorchilus show the highest degree of temporal coordination.  Van Remsen (who voted in favour of three genera) noted previously (in summarising the comments of dissenters) that the "three separate genera … are … morphologically "below" the traditional level of generic distinctiveness".  However, Mann et al. (2009) suggest that the three groups are diagnosable by ecological characters in addition to molecular characters.  As a result, the proposed genera are at least as supportable as some of the N American wrens related to this group.

Given the committee member comments on Proposal 219, changing the genus for S American Thryothorus would appear to be unfinished business.  For those that consider the three genus approach still to be weakly supported, there are two options: (i) reverting to Hellmayr's two genus treatment, which could be regarded as a status quo ante when Thryothorus is properly restricted to N America; or (ii) place all S American Thryothorus in Pheugopedius.  In either of these treatments, the non-recognized genera of Mann et al. (2006) could be treated as sub-genera.  If the SACC later comes to the conclusion that a greater Pheugopedius is not monophyletic, as suggested by Mann et al. (2006, 2009), then a further rearrangement could be considered in future, but this would affect less than half of the species currently recognised in this group if Pheugopedius is used, or just two species if SACC reverts to Hellmayr's treatment.

An unfortunate consequence of Proposal 219 being rejected was that the proposed new linear order was also rejected.  Proposal 408 would re-arrange the genus (whatever its name) so as to reflect the relationships suggested by Mann et al. (2006) and recommended in Proposal 261, which maintain the existing order generally but rearrange to show the suggested three (sub-) genera (together with minor tweaks to the order of the Cantorchilus group), with "incertae sedis" (within Cantorchilus) griseus at the end of the order:

Old linear order

Proposed new linear order

spadix
fasciatoventris
euophrys
eisenmanni
mystacalis
genibarbis
coraya
rutilus
sclateri
nigricapillus
leucopogon
rufalbus
nicefori

leucotis
superciliaris
guarayanus
longirostris
griseus

(sub-)genus Pheugopedius:

spadix
fasciatoventris
euophrys
eisenmanni
mystacalis
genibarbis
coraya
rutilus
sclateri

(sub-)genus Thryophilus:

rufalbus
nicefori

(sub-)genus Cantorchilus:

leucopogon
nigricapillus
superciliaris
leucotis
longirostris
guarayanus
griseus

 

A positive vote on Proposal 408 would result in this new linear order being adopted.

As a result of Proposal 219 not passing, all Thryothorus were moved to Pheugopedius in the Colombian checklist three years ago (Salaman et al. 2007, 2008, 2009) assuming that SACC would also do so in due course based on comments of committee members.  One of the authors of this proposal has sought to adopt such an approach in some journal papers including site/regional checklists and range extensions, but has become somewhat fed up with editors and peer reviewers commenting that these birds should be Thryothorus due to the SACC's treatment (particularly for the "core" Pheugopedius that would be recognised in this genus under Mann et al.'s suggested treatment where 10/10 SACC members supported recognising this genus!).  SACC action on this matter would be welcomed as other persons working with Neotropical birds may have had similar experiences.

(Another approach would be to merge Henicorhina, Uropsila, Cinnycerthia, Cyphorhinus and S American Thryothorus into one genus, but that would cause more nomenclatural instability than it is worth and rob us of some well-defined genera.)

The following votes would have the following results, assuming that proposal 408 (on linear order) passes:

 

409 passes, 410 rejected (or 409 and 411 pass but 410 does not):

409 and 410 pass, 411 does not:

409, 410 and 411 pass:

Pheugopedius:

spadix
fasciatoventris
euophrys
eisenmanni
mystacalis
genibarbis
coraya
rutilus
sclateri

rufalbus
nicefori
leucopogon
nigricapillus
superciliaris
leucotis
longirostris
guarayanus
griseus

Pheugopedius:

spadix
fasciatoventris
euophrys
eisenmanni
mystacalis
genibarbis
coraya
rutilus
sclateri

Thryophilus:

rufalbus
nicefori

leucopogon
nigricapillus
superciliaris
leucotis
longirostris
guarayanus
griseus

Pheugopedius:

spadix
fasciatoventris
euophrys
eisenmanni
mystacalis
genibarbis
coraya
rutilus
sclateri

Thryophilus:

rufalbus
nicefori

Cantorchilus:

leucopogon
nigrocapillus
superciliaris
leucotis
longirostris
guarayanus
griseus

 

References:

Mann, N.I., et al. 2006. Molecular data delineate four genera of "Thryothorus" wrens. Mol. Phylogenet. Evol. 40: 750-759. http://www.tc.umn.edu/~barke042/Publications.php

 

Mann, N.I., Dingess, K.A., Barker, F.K., Graves, J.A., Slater, P.J.B. 2009. A comparative study of song form and duetting in Neotropical Thryothorus wrens.  Behaviour 146, 1-43

 

Recommendations: (From Thomas Donegan): I would strongly recommend a YES vote to 408 and 409; for votes 410-411, I can see reasons why committee members might vote either way.  My own view is that a yes vote is more sensible in both instances.  Mann et al. (2006, 2009) taken together provide a solid rationale for their recommendations and have clearly considered the issues at length.  Their diagnosis of the three new genera now has real world as well as molecular support.  Given that all the genus names of these species will be changed anyway, a priori, their treatment should probably best be followed rather than being second guessed.

(From Keith Barker): I would strongly recommend a YES vote for all four of these proposals, for the reasons set out in Mann et al. (2006, 2009).  However, if Cantorchilus is not to be recognized, I would strongly recommend voting yes on 408-110, taking us to the status quo ante Hellmayr’s lumping of all within Thryothorus, and avoiding placement of taxa into Pheugopedius that have never been there.

Thomas Donegan & F. Keith Barker, August 2009

 

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Comments from Stiles:

“408. YES. The new linear order presented clearly reflects phylogeny better than our current arrangement.

“409. YES, to recognize Pheugopedius; the Neotropical species clearly do not belong in Thryothorus; their inclusion would render this genus polyphyletic.

“From here on, however, things get a bit dicier. The proposal contains some confusion regarding whether the current practice of lumping all into Thryothorus vs. the “two-genus” approach of recognizing Thryophilus and Pheugopedius is due to Hellmayr or is “pre-Hellmayr”.  Looking up what Hellmayr actually wrote in “birds of the Americas” (1934), I find that he indeed lumped all the Neotropical forms (as well as ludovicianus, the only “true” Thryothorus) into a single genus.  However, the idea was not original with him; he was following van Rossem (Trans. San Diego Soc. Nat. Hist. 6, p. 208, date not given) in stating:  “…the differences between Thryophilus, with open nostrils, and Pheugopedius, with partly operculate nasal groove, is so completely bridged by intermediate species that no dividing line can be drawn.  Moreover, the two types of nostrils, used as criteria for generic distinction, even occur within the same species, the case of T. modestus being very appropriately cited by van Rossem as a striking example of such variation.  If Pheugopedius and Thryophilus be merged, there is no valid ground for the retention (sic) of Thryothorus, since a good many species of “Thryophilus” agree with the Carolina Wren in the lesser graduation of the tail.”

“If these were the only features defining Pheugopedius and Thryophilus, their lumping would seem to be in order, but Hellmayr did not give diagnoses for genera. I therefore went to Ridgway (Birds of N. and Middle America, USNM Bull. 50, vol. 3, 1904) for these.  The following table summarizes the points of difference that I was able to extract from Ridgway’s diagnoses:

 

Pheugopedius

feature

Thryophilus

Longitudinal to fusiform

Nostril

Small, round or oval

Decumbent operculum overhangs nostril, posterior end contacting with or overhung by feathers of nasofrontal antiae

Operculum

No operculum, but a naked membrane may extend along upper edge of nostril, separated from nasofrontal antiae

Graduated for 1/3 or more of its length

Tail

Graduated for 1/3 or less of its length

Straight for ≥ _ of its length, abruptly decurved terminally

Exposed culmen

Straight to slightly decurved, gradually decurved terminally

Slightly concave, deflexed basally, slight indication of subterminal notch

Maxillary tomium

Straight to slightly decurved terminally with distinct subterminal notch

Short but distinct, occasionally 1-2 well developed

Rictal bristles

Obvious, 1-3 well developed

Short, rounded; primaries 3-7 or 4-6 longest, 8<<3

Wing shape

Moderate, rounded; primaries 4-7 longest, 8 variable

D(igit) 4 w/o claw reaches to middle of subterminal phalanx of d3, claw reaches base of claw of d3

Length of toes

D4 w/o claw reaches subterminal joint of d4, claw does not reach base of claw of d3

 

As a basis for separating genera, this is cutting it pretty fine, but is fairly typical of generic diagnoses of Ridgway’s time.  I then went to our collection to check out these characters.  Surprisingly, I found that in specimens in which the nasal area was intact, the difference cited by Ridgway does seem to hold in most cases.  All species show a naked membrane partly covering the nostrils but in all of the Pheugopedius, this extends from the dorsal edge of the nasal fossa and does partly cover the nostril – although in some where the membrane has been pulled back, the nostril appears more rounded.  In Thryophilus, this membrane extends from the proximal end of the fossa distally to the nostril, which does indeed appear more rounded – but in a few the dorsal extension is more pronounced, though never so much as in the Pheugopedius.  (We do not have T. modestus here, so I could not check directly van Rossem’s statement.)  The tail is indeed more graduated in Pheugopedius, but in some Thryophilus it approaches pretty closely this degree of graduation.  Regarding the curvature of the culmen, there is much variation within species: the tendency for a more strongly decurved tip in Pheugopedius holds, but some (young?) individuals show a more gradual curvature; a few individuals of several species in Thryophilus have more abruptly curved bill tips, though not so pronounced as in most Pheugopedius.  The same goes for the subterminal notch: though on average it is more pronounced in Thryophilus, one can find the full range of variation in virtually all species.  I did not go into detail regarding wing shape, but again, primary 3 seems to average relatively longer in Pheugopedius but the difference is pretty slight. I could see no consistent difference in the relative length of the toes, and the rictal bristles seemed to vary more according to preparation than anything else.  In conclusion, there is some morphological basis for recognition of Thryophilus as distinct from Pheugopedius but the differences are often slight and bridged by individual variation in many cases (perhaps related to age for bill shape?).  Given that these differences, such as they are, do correlate with the genetic data, I could be induced to vote a lukewarm YES on proposal 410 to recognize Thryophilus (although I would not be surprised – or heartbroken - if many SACC members disagreed with me).

            “However, I could find no morphological character(s) that would convincingly separate Thryophilus (sensu stricto) from Cantorchilus.  I am reluctant to base a genus on zero morphological differences (but if Keith or Thomas wish to conduct a more thorough morphological analysis and do find something, I could go along with it).  The song differences are interesting, but I am also reluctant to use such differences to separate genera in oscines where song learning is pronounced and local song dialects are frequent.  In species like rufalbus, sometimes one hears perfect coordination between males and females (the female adding her notes to the end of the male’s with no discernable break, as in modestus, for example), at other times (especially in minlosi of the Llanos) coordination seems lacking or less developed.  Hence, I will vote NO on 411, at least for the present, though I am willing to recognize Cantorchilus as a subgenus of Thryophilus (or Pheugopedius) based on the genetics.   In passing, I note that the recognition of species in Scytalopus is based to a great extent upon song differences that line up with genetic differences, but here we are dealing at the species, not genus level in a group in which song learning is presumed to be absent.

            “I also note that no genetic data are available for T. griseus, which is morphologically much more distinctive than anything in Pheugopedius or Thryophilus with its much shorter and nearly non-graduated tail and grey coloration (and canopy habitat?).  Not having the song paper I don’t know if its song was included in the pertinent paper of Mann et al., but on the face of it, it might well be worth looking at (we have a recent specimen here, Daniel!)”

 

Comments from Robbins: “YES.  I’m on the fence on this one, as it really doesn’t bother me that Cantorchilus is defined primarily by genetics (vocal data are suggestive).  The morphological differences between the Pheugopedius and Thryophilus clades are so slight that if those were the only data supporting recognition of those two genera then I would vote no on that proposal.  Thus, in an attempt to be consistent, I vote for the recognizing Cantorchilus, although I’m not totally convinced that this is the right course of action.”

 

Comments from Zimmer: “

“Proposal #408:  Change the linear order of current Thryothorus wrens.  YES, our current arrangement does not square with the available evidence.

 

“Proposal #409:  Recognize Pheugopedius.  Again, YES, as the evidence is pretty clear that Thryothorus applies only to ludovicianus/albinucha, and that all of the South American species belong somewhere else.

 

“Proposal #410:  Recognize Thryophilus.  YES, based on the combination of molecular evidence, vocal evidence (as outlined in Mann et al. 2009), and Gary’s assessment of Ridgway’s diagnosis of Pheugopedius versus Thryophilus.

 

“Proposal #411:  Recognize Cantorchilus.  Gary’s points on this one are well taken.  Although there is definite morphological cohesion between most of the species that would be placed in Cantorchilus (superciliaris, leucotis, longirostris, guarayanus), there is little if anything in the way of morphological characters that would allow the genus to be diagnosed relative to Thryophilus.  I also share Gary’s hesitance regarding the use of vocal differences to define a genus of oscine passerines, which can learn their songs.  However, I think that Mann et al are really on to something as regards vocal differences in duetting behaviors in these wrens.  When you read through the list of different singing styles (Table 4 in Mann et al. 2009) it is somewhat confusing because of the sheer complexity of the vocalizations and duetting behaviors involved.  But, if you have field experience with the species involved, you can see the patterns that Mann et al refer to, and many of the species in each proposed “new” genus do sort out as having similar singing “styles”.  It seems to me that the underpinnings that allow males and females of one species to frequently engage in highly coordinated, complex, antiphonal duets, as opposed to those species in which duetting is relatively rare and/or less coordinated are more likely to be genetically based than are simple differences in song dialects, which, in this family, can obviously be learned.  We still don’t really have a handle on what constitutes genus-level vocal distinctions, although I am reminded of that old quote regarding obscenity – “we can’t really define it, but we know it when we see it”.  Clearly, there is more work to be done in refining some of Mann et al’s song style categories, and, as the authors themselves point out, not every species in each proposed genus displays the same song styles.  However, the authors have provided a good platform for investigating the extent of the genetic basis for the differences in vocal behavior in these wrens, and I do think that where there is smoke there is fire.

 

“Gary raised the question of T. griseus, which would seem to be a potential fly-in-the-ointment for any proposed phylogenetic arrangement, because without DNA we really don’t know where it belongs.  Morphologically, it is more different from all other “Thryothorus” than any of them are from one another.  And no, Mann et al 2009 did not have vocal data on griseus in their paper.  However, I find it interesting that under their proposed arrangement, griseus would be in Cantorchilus, as would leucopogon and thoracicus (of Central America).  I recently published a paper detailing observations on vocalizations (including duetting behavior), ecology, and nesting of T. griseus (Zimmer & Whittaker 2009, Cotinga 31:80-85), and off the top of my head, I would say that the singing style of griseus would be closest to Style 9 as defined by Mann et al. (which was published while our Gray Wren paper was in press), with males having different categories of song (series of single tonal notes as well as more complex phrases, both of which are repeated and increase in amplitude through the course of the song), and duets formed by females joining in with complex phrases.  Mann et al. classified both leucopogon and thoracicus as Style 9, and I would strongly agree with that classification.  It is also interesting that both leucopogon and thoracicus show some ecological similarities to griseus, in that all three species tend to forage mostly in low or mid-level vine tangles.  Molecular analysis may ultimately show that griseus isn’t particularly close to any of the other South American “Thryothorus”, but I do find it interesting that ecologically and vocally, it is closer to thoracicus & leucopogon, which molecular data would place in Cantorchilus.

 

“When all is said and done, I have to vote YES on recognizing Cantorchilus along with Pheugopedius and Thryophilus, with the recognition that we may end up moving some of the constituent species between genera as more molecular and vocal data become available (especially as regards griseus).”

 

Comments from Cadena:

409-411. YES to all three proposals. I think we made a mistake when considering proposal 219. Back then, the discussion led to rejection of the proposal because committee members disagreed on whether one should recognize one or three genera for the South American "Thryothorus". This implied that we have maintained a genus that has been convincingly shown not to be monophyletic (owing to the position of ludovicianus).

 

“When discussing proposal 219, I tried to emphasize that the three genera proposed by Mann et al., and now endorsed by Donegan and Barker in these proposals, are strongly supported clades. This suggests that one cannot go wrong by giving names to these groups. In contrast, support for the monophyly of a clade formed by all three proposed genera to the exclusion of other wren genera is nonexistent. Therefore, I contend that recognizing a broad Pheugopedius is untenable with the evidence at hand. I would also like to emphasize that even if the three clades turn out to form a monophyletic group, a classification that ranks each of them at the genus level would be stable (i.e. monophyly of the group would not require making any further changes). In contrast, if we adopt a broad Pheugopedius as suggested by committee members before, and this genus turns out not to be monophyletic (note that the molecular data point in this direction), we will need to revisit the classification of the group once again, leading to instability.

 

“Finally, it is nice to see that there is some evidence from vocalizations, etc. that aids with the diagnoses of the new proposed genera. However, I think that this should not be a requirement to justify changes in situations like this: solid phylogenetic analyses tell us that our current taxonomy is inconsistent with evolutionary history, so we need to change it. It would be nice if all named groups had phenotypic diagnoses, but I believe that it is more important that they represent monophyletic groups. As Kevin said, we might end up needing to move a few species between genera as data accrue in the future, but this is fine. Let's act based on what we already know.”

 

Comments from Jaramillo: “

“Proposal 408. Change linear order of current Thryothorus wrens (II)

Yes – this appears to better fit molecular, as well as behavioural data sets.

Proposal 409. Recognize genus Pheugopedius (II)

Yes – this one is clear based on the data.

Proposal 410. Recognize genus Thryophilus (II)

Yes – Again, this seems to be the right course of action based on molecular data, morphology and voice.

Proposal 411. Recognize genus Cantorchilus (II)

Yes – This was the most problematic one for me. What I found most helpful were the comments by Gary Stiles and then Kevin Zimmer in the argument for whether we should recognize a genus based entirely on molecular characters. The clarification came in how the vocal data is viewed, and I think that Kevin really hit the nail on the head. The vocal data is there and they duet and vocalize in a different way, consistently within each genus, but it is very difficult to describe properly. It is described awkwardly but in print in the Mann paper, so on the whole I am cautious but believe that a yes vote is the way to go on this. Voice is incredibly important in wrens, and in a rather complex manner.”