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" mark. It 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: García-Moreno & Fjeldså
(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:
GARCÍA-MORENO,
J., AND J. FJELDSÅ. 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 Fjeldså 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."