Proposal (569) to South American Classification Committee

 

 

Revise the generic classification of the Mountain-Tanagers

 

Proposal 437G was termed as follows and based on Sedano & Burns (2010)'s phylogenetic study:

"Recognize the genera Sporathraupis for Thraupis cyanocephala, Tephrophilus for Buthraupis wetmorei, Compsocoma for Anisognathus somptuosus and notabilis, and Anisognathus for igniventris, lachrymosus and melanogenys, since they all represent segments of a basal polytomy and are therefore equivalent (at least with current evidence); I recommend a YES. The alternative (NO) would be to lump all four groups into Anisognathus."

 

Five committee members voted in favour of the new arrangement.  Four voted against it and one apparently has not voted.  Because of the quorum / voting rules, the four no-voters meant that the proposal failed.  However, the SACC baseline cannot be changed to reflect the lumping of various species into Anisognathus because any change requires a 70% super-majority (four positive votes are insufficient).  Dr. Remsen asked me to produce this series of proposals and sub-proposals in order to seek to seek to help reaching a consensus on a way forwards for this part of the phylogeny.

 

Burns phylogeny

 

A diagram showing an expanded part of the Sedano & Burns (2010) phylogeny as annotated by Gary Stiles for purposes of the last set of proposals is set out above.  I have further edited it to reflect what seem to be the agreed (7/10+ in favour) outcomes from Proposal 437.  The piece subject to these sub-proposals is the "middle bit" marked red, and in particular the polytomy from Tephrophilus down to Anisognathus.

 

Proposal A: Lump all of Thraupis cyanocephala, Tephrophilus and Anisognathus into Anisognathus.

This proposal is the converse of 437G, expressed positively.  Three committee members were in favour of this change last time.  Five were against it.  One committee member (and Sedano and Burns) supported all of 437G except the lumping of Anisognathus with Compsocoma.  This Part A is raised for completeness such that any procedural questions on 437G can be considered addressed.  An issue with this approach is that the polytomy to be united here is poorly supported (0.74/43), as well as the morphological and behavioural heterogeneity of the resulting treatment.  The node uniting all these is also quite old in terms of substitutions compared to other nodes supporting tanager genera.  Proposals B to D assume that Proposal A would fail (given past votes).

 

Proposal B1: Resurrect Sporathraupis for Thraupis cyanocephala. 

This is probably the most unexpected part of the polytomy.  Being familiar with several Thraupis (including cyanocephala) in the field and hand, I had always found the generic placement of the latter really strange.  It certainly shares dull plumage and general size with Thraupis, but it is behaviourally and ecologically distinct, being montane and mostly in forests / forest borders and reasonably high up in forest strata (cf. secondary growth in lowlands) and differing in its bill morphology and voice.  Whilst it is now shown not to be vaguely related to the ubiquitous Palm and blue-and-white tanagers, neither does cyanocephala look like an Anisognathus.  On the other hand, cyanocephala shares its distribution, habitats, and voice with a broader Anisognathus. 

Resurrection of the available genus name uncovered by Gary Stiles seems appropriate, whilst placing it in Anisognathus (the other alternative) would endorse a relationship that seems bizarre based on the morphology of these birds.  One of those who voted against 437G as well as both Sedano and Burns endorsed this approach in the situation in which no major lumping of mountain-tanager genera is undertaken.

 

Proposal B2: In the event that Proposal B1 fails, place Thraupis cyanocephala in Anisognathus

Please note and bear in mind the conditionality embedded in this proposal.  If B1 fails, leaving this species in Thraupis is not an option and it should therefore be transferred to Anisognathus (as in Proposal A) pending further molecular work on the polytomy.

 

Proposal C1: Resurrect Tephrophilus for Buthraupis wetmorei

Things get less clear-cut here in terms of morphology.  In contrast to cyanocephala, few familiar with these birds would probably have been surprised to find wetmorei more related to Anisognathus than Buthraupis.  This might not sound very compelling as a rationale for lumping, but we placed it next to (on the same page as) the Anisognathus in the McMullan et al. Colombian field guide as a result (rather than on the previous page with Buthraupis) to assist in identification.  In the molecular study, it forms its own part of the polytomy.  Gary Stiles identified this available genus name if it is treated as monotypic.  One of those who voted against 437G as well as both Sedano and Burns endorsed this approach in the situation in which no major lumping of mountain-tanager genera is undertaken.

 

Proposal C2: In the event that Proposal C1 fails, place Buthraupis wetmorei in Anisognathus

Please note and bear in mind the conditionality embedded in this proposal.  If C1 fails, leaving this species in Buthraupis is not an option and it should therefore be transferred to Anisognathus (as in Proposal A) pending further molecular work on the polytomy.

 

Proposal D: Resurrect Compsocoma

Thoughts on this are included in the last proposal and to a large extent published:

“Whatever one’s interpretation of the molecular data, the genus Compsocoma is well-defined morphologically and behaviourally.  We noted in Donegan & AvendaĖo (2010) that: “Blue-winged Mountain Tanager A. somptuosus and Black-chinned Mountain Tanager A. notabilis are more robust birds with stronger flight … but were lumped (with little justification) into Anisognathus by Meyer de Schauensee (1966).  We treat Compsocoma as a subgenus of Anisognathus herein.”  Where the two genera occur together, Compsocoma is often in higher forest strata than Anisognathus and is more mobile.  Several taxa within both a narrow Compsocoma and Anisognathus may require species rank and some of them have been split by modern authors (e.g. C. somptuosus), so the genera produced will probably not be as small long-term as one might initially think.  If one were to ignore history and act only rationally, then recognition of Compsocoma would be sensible based on comparative morphological differences between other tanager genera and now poor support for a monophyletic Anisognathus.  … On balance, I like the idea of recognising Compsocoma. 

A contrary approach and rationale for voting against (based on Burns and Sedano's comments) would be to retain Compsocoma in Anisognathus pending further work on the polytomy.

 

[There is no D1/D2 because Compsocoma is already in Anisognathus.]

 

Note on priority issues: I referred in the previous proposal and the following accompanying note (http://www.museum.lsu.edu/~Remsen/SACCprop437Nomen.html) to priority difficulties affecting Anisognathus.  Mlíkovsky (2012) has done a great deal of research into one of the relevant publications, suggesting that conflicting names Compsocoma and Poecilothraupis were described 1-2 years later than has previously been thought to be the case.  Further work is needed on the publication dates relevant to Anisognathus, but this issue seems more likely to go away as a result of this recent publication.

 

References:

Donegan, T.M. & AvendaĖo, J.E.  2010.  A new subspecies of mountain tanager in the Anisognathus lacrymosus complex from the Yariguíes Mountains of Colombia.  Bull BOC 130(1): 13-32.

Mlíkovsky, J. The dating of Cabanis’s “Museum Heineanum: Singvögel”. Zoological Bibliography 2(1): 18-26 http://www.avespress.com/featured-periodicals/

 

Sedano, R. E. & K. J. Burns.  2010.  Are the Northern Andes a species pump for Neotropical birds? Phylogenetics and biogeography of a clade of Neotropical tanagers (Aves: Thraupini).  Journal of Biogeography 37: 325–343.

 

Thomas Donegan, November 2012

 

 

Comments from Robbins: “The issue is the low node support for taxa within this clade, so unless we include everything within Anisognathus we will end up making additional modifications with new genetic data.  Clearly, wetmorei and cyanocephala cannot be maintained in their current genera, so either we lump everything in Anisognathus or because of the apparent long branches we treat wetmorei and cyanocephala in monotypic genera.  If we do the latter then it seems we have to put notablis and somptuosus in Compsosoma with the rest of the species in Anisognathus.  So, I have no strong preferences on whether we lump everything into Anisognathus until nodes are better resolved or we recognize four genera in this clade.”

 

Comments from Zimmer: “The only part of this that I feel strongly about is that cyanocephala needs to be removed from Thraupis, and that it also does not belong with the other mountain-tanagers in a broad Anisognathus (to which, I otherwise do not have strong objections).  So, by voting NO on Part A, and YES on Part B1, it follows that B. wetmorei should also be placed in a monotypic Tetrophilus (so, YES on C1), which, in turn, for consistency, means resurrecting Compsocoma for somptuosus and notabilis (so, YES on D), with everything else in Anisognathus.”

 

Additional comments from Stiles: “As the one who originally proposed splitting this polytomy into four genera, I will stand pat on this one: all four are quite diagnosable, the polytomy is quite basal, and this best expresses current knowledge.  Most of the disagreement was that it would be better to await more data to better resolve the polytomy, but since none has been forthcoming, I prefer to go ahead with the four-genus arrangement. In any case, SACC decisions are based upon the available evidence and not graven in stone, so if and when the polytomy gets resolved, I won't be averse to changing my opinion.”

 

Comments from Pacheco: “Até uma melhor definićčo das interrelaćões, eu também prefiro o tratamento para esse conjunto em quatro gźneros. Thus, NO to A; Yes to B1; Yes to C1.”

 

Comments from Nores: “YES to A, meaning to include all Thraupis cyanocephala, Buthraupis wetmorei, Anisognathus notabilis and A. somptuosus in Anisognathus. Although this arrangement does not convince me much, I am not convinced that it is better to resurrect three new genera, and addressing this issue, it seems more convenient to keep things as they are today. What I think it is necessary is that cyanocephala be removed from Thraupis and wetmorei from Buthraupis, and a barely acceptable solution is to put them into Anisognathus.”

 

Comments from Pérez-Emán: “Barker et al. (2013, 2015) have published some analyses on the New World clade Emberizoidea, including updated molecular information on Thraupidae. Although there are just few new species included in it, data from molecular and nuclear loci are included. Due to complexities associated to large amount of data, a phylogenetic analysis was based on a supertree approach and results (including most Emberizoidea) are presented (Barker et al 2015, and figures with nodal support are found in their supplementary files S1 and S2). The case for the polytomy we are discussing in this proposal is interesting. The topology is somehow different leading us to consider a broader group: all previous Buthraupis, Chlorornis, all Anisognathus and Thraupis cyanocephala. It is the same polytomy shown in Sedano and Burns (2010) but this proposal and previous one (437) concentrated in just a subsample of this group. Another difference is the arrangement of taxa in the phylogenetic hypothesis. All Buthraupis are grouped together, including Chlorornis; the same for Anisognathus and, separate from them is Thraupis cyanocephala. This is a totally congruent topology to the one published by Sedano and Burns (2010) considering the low support (posterior probabilities) of many of the nodes relating these taxa. However, I wonder if the taxonomic discussion leading to resurrecting many of these genera names had been started if it weren’t by the topology shown in Sedano and Burns (2010), particularly in the case of Buthraupis and Anisognathus. But the heart of the issue is that our taxonomy should be based on complete evidence and not just in a particular set of characters (e.g., morphology, molecular information). We could lump Chlorornis into Buthraupis and keep Anisognathus as it is. However, morphological, ecological and behavioral characters, as well as low support for many of the phylogenetic relationships found in these studies, are in favor of recognizing Sporathraupis for Thraupis cyanocephala (B1), Tephrophilus for Buthraupis wetmorei (keeping eximia and aureodorsalis in Cnemathraupis) (C1), and Compsocoma for Anisognathus somptuosus and A. notabilis (D).

 

Comments from Areta: “Since this proposal was written, a recent relevant paper by Barker et al. (2015) has appeared. Despite some important changes in the phylogenetic position of the involved taxa, the generic-level problems subject of this proposal still linger. Nevertheless, these important differences in phylogenetic placement should serve as a warning on making decisions based on polytomies that may disappear or change notably in subsequent studies.

 

A-I would recommend a NO, to do this would imply (according to Barker et al. 2015) to merge also Chlorornis and Cnemathraupis in Anisognathus.

 

B- I would recommend a YES to B1. Given the long branch and consistent isolation in both molecular works, in addition to distinctive morphology, Sporathraupis cyanocephala seems the way to go.

 

C- I would recommend a YES to C1. Note however that in the recent paper by Barker et al. (2015) Tephrophilus wetmorei was found to be sister to Buthraupis montana, making it possible for it to be retained in Buthraupis. Nevertheless, long branches and very different external appearance support the inclusion of wetmorei in a different genus.

 

D- I would recommend a YES to D. Compsocoma is separated from the remainder of Anisognathus by deep branching and is morphologically coherent (yellow nape and plain-black face without facial markings), thus I favor its recognition, which is also consistent with treatment of other genera in the group.”

 

Comments from Stiles: “A-NO; with such long branches, lumping everything into Anisognathus produces a heterogeneous soup.  B1. YES. plumage and bill morphology suggest that cyanocephala is best placed in its own genus.  However, I note that this (B2) is the lumping I’d feel least uncomfortable with, given the similarities in ecology etc. with Anisognathus – plumage is different but could represent simply an Anisognathus type in which the head pattern had become obsolete, although the bill still differs.  C1. YES. Wetmorei is clearly the most divergent form in this entire group in size, heavy bill, etc. and because it clearly does not ally with Buthraupis in the phylogeny, it surely seems entitled to its own genus here.  D. YES. The two species of Compsocoma differ strongly in bill shape as well as being distinguishable in plumage, ecology and voice from the “true” Anisognathus species.”