Proposal (86) to South American Classification Committee
Treat the taxon melanolaemus as a
subspecies of Atlapetes rufinucha
Effect on South American CL: This proposal would lump two taxa
that we treat as separate species into a single, more traditional Atlapetes
rufinucha.
Background: The taxon melanolaemus has
traditionally been treated as a subspecies of Atlapetes rufinucha;
they are evidently parapatric, with the barrier, if it exists, probably being
the dry upper Madidi valley in northern depto. La Paz, Bolivia. Melanolaemus
looks like nominate rufinucha except that its breast is markedly
clouded to varying degrees with irregular blackish markings; also, its head is
more extensively black, connecting the black face to the black malar streak and
lacking the pale marks in the loral area of nominate rufinucha.
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. Of particular relevance to this proposal is that the 2nd-highest
bootstrap value in their tree (72%) was between nominate rufinucha and Atlapetes
fulviceps, the parapatric species that borders the southern distribution
of A. rufinucha; also, melanolaemus clusters with a set
of parapatric taxa from southern Peru, A. melanopis, A.
canigenis, and A. forbesi. The low bootstrap values for this
"southern Peru" group mean that it should not yet be taken seriously,
despite its geographic "sense"; regardless, if the rufinucha-fulviceps
node is solid, then that would make traditional rufinucha a paraphyletic
species without the removal of melanolaemus.
For that reason, and the lack of any signs of intergradation despite
their presumed parapatry, beyond a single suspicious specimen, García-Moreno
& Fjeldså (1999) elevated melanolaemus to species rank, and this was
followed by Dickinson (2003). No comparative data on vocalizations have been
published.
Analysis: The data for species rank of melanolaemus are fairly
weak. The genetic data are intriguing but weak by current standards. The
contact zone, if there is one, has not been studied, and that single specimen
(at LSUMZ) may indicate some gene flow between them, although it is ca. 100 km
south of the potential contact zone, and no other specimens from the area show
any phenotypic sign of intermediacy. [As an aside, I personally do not object
strongly to paraphyletic species ... I know this is heresy among strict
phylogeneticists, but in my opinion, phylogenetic analyses are not intended for
population-level processes in which problems with lineage-sorting and gene
trees are inevitable; Willi Hennig himself explicitly noted that cladistic
analysis was inappropriate at the population level for this reason; it seems
likely to me that historical gene flow among adjacent populations requires that
he label "monophyletic" at the population level refers only to the genes
analyzed and to the current time period.]
An argument in favor of retaining species rank for melanolaemus
could be constructed as follows. The genetic data, weak as they are, are
nonetheless consistent with species rank. The geography of phenotype
distribution is also consistent with species rank; these two taxa may be
parapatric with no sign of substantial gene flow, or if separated at all, it is
by a narrow dry valley. Melanolaemus, by virtue of its more extensively
black face, shows a fundamental difference in head pattern from nominate rufinucha
that might affect mate selection; these pattern differences are actually
greater than those between the head patterns of nominate rufinucha and
the latinuchus species group further north. Parapatric Atlapetes
canigenis also shows this "expansion" of black in the facial
area, suspiciously similar to that of melanolaemus. As emphasized by
García-Moreno & Fjeldså (1999), minor differences in Atlapetes brush-finches
seem to "matter" in that there are no known cases of zones of
intergradation or hybridization among parapatric taxa. Even In concert, these
arguments are fairly weak, but perhaps stronger than the arguments for the
traditional classification.
Recommendation: I tentatively vote NO on this one (i.e.,
stick with current classification). Although the evidence is weak for species
rank of melanolaemus, I think that the "burden of proof" in
this falls on the case for considering it conspecific with Atlapetes
rufinucha.
Literature Cited:
DICKINSON,
E. C. (ed.). 2003. The Howard and Moore complete checklist of the birds of the
World, Revised and enlarged 3rd Edition. Christopher Helm, London, 1040 pp.
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.
Van Remsen, December 2003
P.S.: If this proposal doesn't pass, then I'll do a proposal on
the English name of melanolaemus, for which there are two competing
choices.
____________________________________________________________________________________________
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, although the evidence
for separate species status is somewhat weak."
Comments from Robbins: "[NO] Although the evidence
certainly isn't compelling for treating melanolaemus as a species, the
data for considering it as a subspecies is even less. Hence, I vote for
following the "status quo". A "no" vote.
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 Schulenberg: "YES. I think that someday
we should vote on the split of Atlapetes rufinucha rather than take
the new arrangement for granted. The split may fit with our world view, but in
concrete terms has poor support."
Comments from Jaramillo: "NO. Somewhat reluctantly, because of the poor data
involved. However, there is a paper that exists and proposes a phylogenetic
organization that makes sense in terms of biogeography, and lack of
intermediate specimens, etc. Although poor, this piece of work does shift the
burden of proof in my mind. Until someone performs a stronger analysis that
refutes this, we should keep this taxon as a separate species."
Comments from Nores: "NO, yo voto en contra de considerar a Atlapetes melanolaemus como
una subespecie de A. rufinucha. Pienso que las características
morfológicas, genéticas y su distribución parapátrica sin intergradación tienen
suficiente peso como para asignar nivel de especie a melanolaemus.
No obstante, el razonamiento de Stotz es también convincente."