Revise generic boundaries in the Buteogallus group (2)

 

Proposal (492) [revised] to South American Classification Committee

 

Effect on South American CL: This merges Harpyhaliaetus and “Leucopternis” (the temporary designation for former Leucopternis species definitely not members of that genus) into Buteogallus, except for “L. plumbeus”, which would become Cryptoleucopteryx plumbeus.

Background & New Information:  Our current classification looks like this after passage of proposal 460, which moved true Leucopternis and relatives near Buteo:

“Leucopternis” plumbeus Plumbeous Hawk
“Leucopternis” schistaceus Slate-colored Hawk
“Leucopternis” lacernulatus White-necked Hawk
Buteogallus anthracinus Common Black-Hawk
Buteogallus aequinoctialis Rufous Crab Hawk
Buteogallus urubitinga Great Black-Hawk
Buteogallus meridionalis Savanna Hawk
Harpyhaliaetus solitarius Solitary Eagle
Harpyhaliaetus coronatus Crowned Eagle

For several years, we’ve had plenty of indication that the current boundaries of genera in the vicinity of Buteogallus in our current classification are a mess.  Raposo do Amaral et al. (2009) have produced a comprehensive phylogeny of buteonine hawks, and their data will form the primary basis for this proposal.  Findings from earlier papers (see Notes below) are largely consistent with Raposo do Amaral et al. (2009) and will not be discussed further.  Two of the relevant Notes from our SACC classification are:

14b. Buteogallus urubitinga was formerly treated in the monotypic genera Urubitinga (e.g., Hellmayr & Conover 1949) or Hypomorphnus (Pinto 1938, Friedmann 1950, Phelps & Phelps 1958a), but see Amadon (1949) and Amadon & Eckelberry (1955) for rationale for placement in Buteogallus. Genetic data (Lerner & Mindell 2005), however, indicate that Buteogallus urubitinga and B. anthracinus are not sisters and that the former is more closely related to Harpyhaliaetus (see also Amadon 1949, Raposo et al. 2006). Raposo do Amaral et al. (2009) recommended that they be treated in the genus Urubitinga.  SACC proposal to revise generic limits in Buteogallus and relatives did not pass.

 

15. Buteogallus meridionalis was formerly (e.g., Pinto 1938, Hellmayr & Conover 1949, Friedmann 1950, Phelps & Phelps 1958a, Meyer de Schauensee 1970) placed in the monotypic genus Heterospizias, but most recent classifications follow Stresemann & Amadon (1979) and Amadon (1982) in merging this into Buteogallus. <incorp. Griffiths (1994)> Recent genetic data (Raposo et al. 2006, 2009, Lerner et al. 2008) indicate that Buteogallus is paraphyletic with respect to Harpyhaliaetus and certain Leucopternis. SACC proposal to revise generic limits in Buteogallus and relatives did not pass. Buteogallus meridionalis was formerly (e.g., Peters 1931, Friedmann 1950) placed in the subfamily Accipitrinae, but Plótnik (1956a) showed that morphological data favored placement in the Buteoninae, as confirmed by genetic data (Lerner et al. 2008, Raposo do Amaral et al. 2009).

 

Raposo do Amaral et al.’s (2009) taxon sampling (105 specimens, 54 species) and gene sampling (6000 bp of 9 genes, mitochondrial and nuclear) is exemplary.  I doubt that anyone will produce a better data set anytime soon.  This proposal deals only with their Group H, whose monophyly has excellent support; the relevant portion of their tree (from their Fig. 3) is pasted in here:

 

 

Therefore, the problems in current classification are even worse than revealed in earlier papers, with most species requiring a change in genus.  Raposo do Amaral et al. had to name two new genera to avoid combining all species into one large, heterogeneous Buteogallus.  The latter solution is actually an alternative to be explored if this proposal does not pass.  Group H includes all the taxa previously associated with Buteogallus, within which generic limits have been historically fluid, and adds in three species from Leucopternis, two of which are dark like most of the Buteogallus group but also one (lacernulatus) that has more typical black-and-white Leucopternis plumage.  What a mess.  At least one of the former Leucopternis, schistaceus, has a riverine habitat like its new sister taxa, Buteogallus sensu stricto.

 

Analysis and Recommendation: Virtually every critical node in Group H’s tree has strong support.  Therefore, the only point of real discussion is the subjective exercise of how broadly to delimit the genera.  Raposo do Amaral et al. have defined these very narrowly, but a proposal (459) to adopt that classification (see below) did not pass.

Cryptoleucopteryx plumbea (the new genus is feminine)
Buteogallus anthracinus (includes “subtilis”)
Buteogallus aequinoctialis
Buteogallus schistaceus
Heterospizias meridionalis
Amadonastur lacernulatus
Urubitinga urubitinga
Urubitinga solitarius
Urubitinga coronatus

 

The option at the other extreme would be to expand Buteogallus to include all nine species in Group H.  However, I am persuaded by the comments (see 459) of Kevin Zimmer and Bret Whitney, and by Gary Stiles’s comments below (originally submitted as a NO vote to the previous version of this proposal that was for a single broad Buteogallus) that the outlier, “L.” plumbeus, placed in a newly described genus Cryptoleucopteryx, merits a monotypic genus.  Although no single character diagnoses it, it has a unique combination of characters, and plumbeus is also an oddball in terms of voice and behavior.

 

A YES vote would be to adopt the following classification by merging Harpyhaliaetus and two “Leucopternis” into Buteogallus to produce the following classification (which includes a minor sequence change mentioned by Manuel in 459):

Cryptoleucopteryx plumbea
Buteogallus schistaceus
Buteogallus anthracinus
Buteogallus aequinoctialis
Buteogallus meridionalis
Buteogallus lacernulatus
Buteogallus urubitinga
Buteogallus solitarius
Buteogallus coronatus

 

As expected from a decision that is largely subjective, the comments on 459 were all over the place in terms of preference, but at least a couple of you were in favor of broad Buteogallus.  A point against such a treatment is that if you look at the big tree in Raposo et al., the node (H) that unites a broad Buteogallus is deeper than the points on the x-axis (substitutions/site) as the nodes that mark most generic limits we adopted for the buteonines in proposal 460; so based purely on comparable degree of genetic differentiation, a broad Buteogallus is within those limits but at the extreme.  On the other hand, the depth of that node is driven entirely by plumbeus – if not for that species, the node would be at the opposite end of the range of the depths that mark generic boundaries in the buteonines.  To maximize consistency based on genetic differentiation, a solution would be to adopt Cryptoleucopteryx for plumbeus and keep the rest in Buteogallus (a solution mentioned by Doug in his comments on 459).

 

Literature Cited:

RAPOSO DO AMARAL, F., F. H. SHELDON, A. GAMAUF, E. HARING, M. RIESING, L. F. SILVEIRA, AND A. WAJNTAL.  2009.  Patterns and processes of diversification in a widespread and ecologically diverse avian group, the buteonine hawks (Aves, Accipitridae). Molecular Phylogenetics and Evolution 53: 703-715.

 

Van Remsen, August 2011

 

 

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Comments from Stiles:  “YES.

“1. I definitely favor placing plumbeus in Cryptoleucopteryx, based largely on Kevin`s comments on the previous proposal and the large genetic distance to the rest of the "Buteogallus group". I am not disturbed by the "lack of a single diagnostic character": a unique combination of characters serves to diagnose many avian genera.  The single-character requirement harks back to a century ago, when such characters in taxonomic keys dictated generic boundaries - rather like putting the cart before the horse. Actually, we haven't been all that consistent in use of genetic vs. morphological-ecological-behavioral features and generic boundaries in any case ... after all, we recognized Cantorchilus based on genetics when the morphological evidence was, as far as I could tell, zero, and did not recognize Diglossopis as separate from Diglossa based on relatively short genetic distances but in the face of considerable morphological, behavioral and ecological differences.  And there have yet to be advanced good morphological diagnoses for some genera in Furnariidae (e.g., the Asthenes-Schizoeaca assemblage). So, it comes down to rather subjective decisions in any case regarding how to weigh the different types of evidence when they do not coincide neatly.

“2.  Regarding placing all the remainder of this group in a broad Buteogallus, I could buy it, albeit with some reservations.  The only real oddball (at least in terms of appearance) is lacernulatus, but genetics strongly favors including it, especially if we also include meridionalis, which I find much less surprising: its juvenile plumage is decidedly buteogalline, its coloration as adult is not so unlike aequinoctialis, its vocalizations are also not greatly unlike some Buteogallus.  Although more terrestrial than others, urubitinga also forages much on the ground and has decidedly longish legs as well.  I have already remarked upon the resemblance of solitarius and urubitinga, such that I see no objection to considering these as congeners, which pretty much bridges the gaps; so, unless there is strong support for the original proposal of Raposo et al. (including two monotypic genera for meridionalis and lacernulata and separating Urubitinga), the next best choice would indeed be two genera: Cryptoleucopteryx and Buteogallus.”

 

Comments from Robbins: “YES.  This is a subjective decision, but as I mentioned in my comments on proposal # 459, the vocal and morphological variation within a broadly defined Buteogallus are no more than that found within Buteo.  With regard to genetic variation and consistency among nodes in taxonomy and nomenclature, I'm fine with placing plumbeus in a monotypic genus.  This is somewhat analogous with what we did in naming a new genus for the highly genetically divergent, but morphologically indistinct (vocalizations are still unknown), Malagasy Gactornis "Caprimulgus" enarratus (although that was a very long branch).”

 

Comments from Pacheco: “YES.  Um relutante sim. Eu, particularmente, preferia o arranjo com utilização de mais gênero tal qual proposto no artigo de Raposo do Amaral et al. 2009. Concordo, todavia, que essa solução é factível em vista da árvore produzida a partir da mesma análise.”

 

Comments from Cadena: “YES. I am not a great fan of monotypic genera; whenever possible, unless one is truly dealing with hoatzin-like oddballs, I prefer having genera with more than one species. I believe this increases the information content of the classification because one immediately knows that two species in the same genus are close relatives, whereas if one has two separate monotypic genera for sister lineages, their close affinity is essentially unknowable based on the names alone. Thus, I like the expanded Buteogallus over the use of the two monotypic genera Amadonastur and Heterospizias. I'll take other's word that plumbea is the hoatzin equivalent in these raptors (I am afraid I do not know all these taxa all that well), so I am OK with Cryptoleucopteryx.”

 

Comments from Jaramillo:  “YES.  I think that this is a good resolution to this problem. Using a monotypic genus for plumbeus is the better solution as opposed to a broad and genetically too (?) divergent single Buteogallus that includes all of the species. Having a broad Buteogallus is a benefit, and a better solution in my mind, than is separating it out into 3-4 genera.”

 

Comments from Zimmer: ““YES.  I agree with Fernando in having a preference for more narrowly defined genera, although readily acknowledge that having a bunch of monotypic genera isn’t all that informative.  I think Van has come up with a good compromise in this case, by recognizing the distinctiveness of plumbeus by placing it in a monotypic genus Cryptoleucopteryx, and placing everything else in a broadly defined Buteogallus.  As Gary points out, it is not much of a stretch to see the similarity of meridionalis to urubitinga (ecologically, morphologically [especially as regards juvenile plumage], vocally) and to aequinoctialis (plumage characters of adults and juveniles).  Same goes for the two species of Harpyhaliaetus and for schistaceus and anthracinus.  The one that still doesn’t feel right is lacernulatus (which is pretty different morphologically, is a forest interior hawk that frequently soars, etc.), but then we have to contend with the genetic data and the apparent close relationship between lacernulatus and meridionalis.  All in all, I think this is a good compromise.”