Proposal (87) to South American Classification Committee

 

Treat the taxon terborghi as a subspecies of Atlapetes rufinucha

 

Effect on South American CL: This proposal would lump two taxa that we treat as separate species into Atlapetes melanolaemus (or into a single, more traditional Atlapetes rufinucha, pending outcome on #86).

 

Background: The taxon terborghi was described by Remsen (1993) as a subspecies of the broadly defined A. rufinucha. It is endemic to the Cordillera Vilcabamba in depto. Cuzco, Peru. Terborghi stands out from any taxon in the former A. rufinucha complex in being greener and darker ventrally. It shares with A. melanolaemus (s. Cuzco to n. La Paz; not parapatric with terborghi "because" they are separated by A. canigenis) an absence of loral spots and an extension of the chestnut crown to the bill (not separated by black, as in nominate rufinucha), but differs in lacking the dark breast markings of melanolaemus and in having at least a small black "whisker" markIt further differs from nominate rufinucha in having a less conspicuous "whisker". It differs from both melanolaemus and nominate rufinucha in having a slightly paler back, showing some contrast with head. There are no comparative data on vocalizations.

 

New information: Garc’a-Moreno & FjeldsŒ (1999) found that the "species" Atlapetes rufinucha was polyphyletic, with the northern form, A. latinuchus, more closely related to nominate A. schistaceus than to A. rufinucha. This was based on a very small (275 bp) portion of the cytochrome-b gene, and the bootstrap values are unimpressive (and I doubt that these results would be publishable in 2003). Nevertheless, their resulting tree shows sufficient geographic structure, with adjacent Atlapetes usually appearing as sisters, so I suspect that many of the results will hold up with larger data sets.

 

They did not have tissue from terborghi but ranked it at the species level with the following statement:

 

"The four forms [canigenis, terborghi, melanolaemus, melanopis] constituting the 'central branch' could be treated as polytypic species. However, each of the constituent forms is more distinctive (morphologically and by mtDNA divergence) than many other brush-finches currently admitted species rank. Although we fail to recognize physical barriers that could separate terborghi, canigenis, and melanolaemus, we know of no evidence of intergradation between them."

 

One could easily find fault with portions of this reasoning, especially given the presumed isolation of terborghi and the lack of a DNA sample from it.

 

Analysis: The data for species rank of terborghi are weak. Nonetheless, the argument could be made that terborghi is at least as distinctive phenotypically as melanolaemus and nominate rufinucha are from each other, and so if melanolaemus is treated as a species, then certainly terborghi should also be so treated. On the other hand, it is more difficult to justify treatment of terborghi as a separate species from A. melanolaemus, but they do differ more dramatically in color of the underparts than any Atlapetes taxa currently treated as conspecific.

 

Recommendation: I tentatively vote NO on this one (i.e., stick with current classification). Although the evidence is weak for species rank of terborghi, I suppose that the "burden of proof" in this falls on the case for considering it conspecific with Atlapetes melanolaemus or A. rufinucha, or making a change from our current classification.

 

Literature Cited:

GARCêA-MORENO, J., AND J. FJELDS. 1999. Re-evaluation of species limits in the genus Atlapetes based on mtDNA sequence data. Ibis 141: 199-207.

REMSEN, J. V., JR. 1993. Zoogeography and geographic variation in Atlapetes rufinucha (Aves: Emberizinae), including a distinctive new subspecies, in southern Peru and Bolivia.  Proc. Biol. Soc. Wash. 106: 429-435.

 

Van Remsen, December 2003

 

 

Comments from Stiles: "[NO]. I agree that the evidence is not overwhelming, but it is a shade better than the evidence for the contrary - and solid contrary evidence should be forthcoming to change the "status quo". NO to both (maintain species status, at least for now)."

 

Comments from Zimmer: "[NO] Once again, the evidence for maintaining as separate species is weak, but I vote "NO". Maintaining our current status quo is at least consistent with how other forms in the genus are treated."

 

Comments from Robbins: "[NO] To be consistent with my vote in proposal # 87 I vote "no". Given the evidence at hand we can't treat melanolaemus as a species and not terborghi."

 

Comments from Stotz: "YES, for lumping all of these into rufinucha. I have to say that I hardly consider the splitting of these species as the "status quo." To me the status quo is the broad rufinucha, which we had until 1999. Van is correct to point to the short piece of DNA used in the Garcia-Moreno and FjeldsŒ study and to note the weak support for the taxa that they suggest. There are only two branches with over 50% bootstrap support. They support a northern clade, and a sister relationship between rufinucha and fulviceps. I am willing to overlook this because of the shortness of the segment of DNA that was studied.  My personal feeling is that we would be better off with the original 4 species (schistaceus, rufinucha, rufigenis and tricolor) with the recognition that there are problems that need to be solved, but as that is not currently on the table, I don't think placing terborghi, melanolaemus and rufinucha into a single species conflicts with any of the results of the 1999 in a significant way. Terborghi and melanolaemus occupy basically adjacent areas to canigenis, but only if you believe the poorly supported results and believe that species have to be monophyletic is that a problem. Finally, I have to say that it seems strange to me that we completely follow the novel arrangement suggested based on very weak data for these brush-finches, while Poospiza whitii and Hyloctistes virgata are not split."

 

Comments from Jaramillo: "NO -- partly to be consistent with 86, but even more reluctant in this case."

 

Comments from Nores: "NO, yo estoy de acuerdo de considerar a Atlapetes terborghi como una full especie. Es un caso muy similar al de la propuesta 86."

 

Comments from Schulenberg: "YES. My sentiments as per Doug's."