Proposal (545) to South American Classification Committee
Recognize
newly described Capito fitzpatricki
Effect on South American CL: This proposal would add a newly described species to the list.
Background: Seeholzer et al. (2012) discovered a new barbet
from the east slope of the southern Cerros del Sira, Ucayali, Peru, that they
described as a new species. Their conclusion that this taxon represents a new
species is based on phylogenetic and population genetic analyses of
mitochondrial DNA sequences of the new species and C. wallacei from
which the authors concluded that they are reciprocally monophyletic sister
species. The new species is diagnosable by plumage and morphology from C.
wallacei and is apparently endemic to a small region of montane cloud
forest in the southern portion of the Cerros del Sira.
Recommendation:
Based on the information provided, I think that Capito fitzpatricki is a valid new species. I recommend a
"yes" vote to add this newly described barbet to the South American
list.
References:
O’Neill, J. P., D. F. Lane,
A. W. Kratter, A. P. Capparella, and C. Fox J. 2000. A
striking new species of barbet (Capitoninae: Capito) from the eastern Andes of Peru. Auk
117: 569-577.
Seeholzer, G. F., B. M. Winger,
M. G. Harvey, D. Cáceres A., & J. D. Weckstein 2012. A new species
of barbet (Capitonidae: Capito) from the Cerros del Sira, Ucayali, Peru. Auk 129: 1-9.
Manuel A.
Plenge, September 2012
Comments from Zimmer: “YES.
I am somewhat on the fence as to
whether this new taxon should be recognized at the species-level or merely as a
new subspecies of the recently described species C. wallacei. Genetic
distance is small relative to other species-pairs in the family, although I
don’t consider that a deal-breaker by itself. The morphological distinctions primarily involve flank color
and the width and tone of red of the breast band. These are clearly diagnostic enough that the two taxa
satisfy PSC criteria as separate species, but the question is one of whether or
not these two allopatric taxa are sufficiently distinct as to be recognized as
species under the BSC.
Unfortunately, we have no vocal samples that can be analyzed, and only
the assertion that the calls and songs of fitzpatricki
are qualitatively similar to those of wallacei. That leaves us with the plumage
differences, which, although striking, are limited. If we look at the Capito
auratus group, we can see taxa with similar plumage distinctions that are
recognized only as subspecies. The
split of C. niger
from C. auratus was justified by
marked vocal differences and lack of evidence of hybridization in the contact
zone; neither sort of evidence is available to us in evaluating the present
case. In the case of the currently
constituted C. auratus, we are
talking about a lowland species with a relatively continuous distribution in
which the various subspecies replace one another across river barriers, but
seemingly, with some intergradation in the contact zones. Conversely, in the current case, we are
dealing with two montane taxa that are isolated by some 400 km from one
another, with broad, intermontane gaps in between. The genetic data indicate that fitzpatricki and wallacei
are relatively recently separated from one another, but the separation is real
– they do appear to be on independent evolutionary trajectories at this
point. Perhaps
the best “yardstick” to gauge them by is provided by a pair of tanagers, Tangara argyrofenges and T. phillipsi, the latter of which, like C. fitzpatricki, is restricted to the
Cerros del Sira (albeit the northern part of the range). Plumage distinctions between the two
tanagers are comparable to those between the two barbets, and I’m guessing that
vocal differences are also comparable in extent. Given that we treat these two tanagers as distinct species,
I’m willing to do the same with the barbets.”
Comments from Stiles: “A weak
YES, for much the same reasons as Kevin.
The plumage differences could go either way (species or subspecies) and
the genetic differences are decidedly borderline; in the absence of analyses of
vocalizations, the decision comes down to whether one considers the distance between
fitzpatricki and xxx sufficient to assure that they are on separate evolutionary
trajectories - a sticky point, to be sure. Although the two forms are basically foothill or lower
mid-elevation forms, they are fairly strong-flying canopy birds such that ca.
400(?) km of continuous lowland forest might be less of a barrier than, say,
the few km of open water separating Venezuela and Trinidad for a weak-flying
forest-interior motmot. Like
Kevin, I come down to precedent - there are a number of fairly comparable cases
in tanagers, warblers etc. where we upheld species status for two forms showing
differences of similar magnitude.”
Comments from Cadena: NO, although I believe this is a spectacular finding and I very much
congratulate the people involved in the discovery. This is definitively a
borderline case, and the authors clearly indicate in the paper that fitzpatricki indisputably is a new
phylogenetic species (i.e., a fully diagnosable population), but that the
evidence that it is a previously unknown biological species (i.e., a
reproductively isolated population) is far less certain. Like Kevin and Gary
said, the evidence is not overwhelming, and there are multiple cases in our
baseline taxonomy in which marked geographic variation in plumage between
allopatric populations is recognized at the subspecies and not the species
level. There is some (small) genetic differentiation, but this is not surprising
considering the geographic isolation of wallacei
and the new form, and this tells us little about the odds of reproductive
isolation. We have no quantitative data on vocal variation. What else could we
use? Kevin rightly emphasized in his analysis the degree of phenotypic
differentiation between other Sira endemics and their closest relatives, but I
suggest we should also look at the degree of phenotypic variation that we
"tolerate" within species of barbets. An example that immediately
comes to mind is Eubucco bourcierii, in which there is
considerable geographic variation in the extension of red plumage in the
underparts among other things, and we still treat populations as conspecific.
This, however, may be a bad example because of known differences in vocalizations
and because work in progress by A. Cuervo shows strong genetic structure, which
may lead to recognition of several species. Consider then the case of E. versicolor, in which forms glaucogularis and versicolor are well differentiated phenotypically (males are quite
distinct), yet they are treated as subspecies of a single species and they
hybridize in Ayacucho/Cusco. The case of E.
richardsoni is also noteworthy, with (as per illustrations in the HBW)
quite striking plumage differentiation within a single recognized species. Take
also the case of the Capito niger complex. With the recognition of auratus, brunneipectus, and niger as separate species, within-species plumage variation
decreased substantially relative to earlier classifications lumping them in a
single species, but it is still quite considerable within the polytypic auratus in terms of carotenoid and
melanic coloration. In addition to plumage variation, genetic differentiation
between supposedly conspecific populations of auratus separated by rivers is quite large (much higher than
between wallacei and fitzpatricki). This all suggests to me
that assigning subspecies rank to fitzpatricki
following the BSC would be a better course of action (despite these populations
being on quite clearly separate evolutionary trajectories); hence my tentative
vote for NO. I wonder whether people who have worked extensively on barbets
(e.g., Dan Lane) could contribute to the discussion with some additional
insights I might be missing.”
Comments from Pacheco: “NO. Aceitando que a descrição claramente indica o
tratamento específico apenas sob o PSC e, evidentemente, pelo arrazoado de
Cadena.”
Comments solicited from Dan Lane: “To be honest, I was hoping to sit on the
sidelines on this case and see what the SACC would do with it, but several
folks have asked for my opinion… so here it is. As the previous commentators
have said, the taxonomic status of Capito
fitzpatricki vis-à-vis the BSC is about as difficult to resolve as they
come. The taxon certainly is a valid named taxon (and quite an attractive one
at that!), and as such is clearly a species under the PSC, but its allopatric
distribution, similarity of plumage, general habitat and elevational range, and
(based on anecdotal reports by the authors) voice would suggest that it is
rather closely related to C. wallacei …
not to mention the sister relationship recovered by the molecular phylogeny in
Seeholzer et al. The most obvious differences in plumage are carotenoid-based
(red, orange, yellow) pigments, with minor melanin-based pigment differences;
some morphometric differences (primarily in bill dimensions) also exist. When
compared to other New World barbets, it is clear that perhaps the easiest
plumage characters to change are carotenoid pigments: witness the subspecies of
Capito maculicoronatus, C. auratus (also see the next
paragraph), and Eubucco richardsoni,
and E. bourcieri and E. versicolor. Thus, based on these
pigmentation differences between fitzpatricki
and wallacei, I’d say that they fit
best with a subspecies relationship. It is a shame that Seeholzer et al. were
not able to get recordings of song of fitzpatricki,
as it would be instructive to see just how similar it is to voice of wallacei, and this perhaps would be the
best way to judge reproductive isolation using phenotypic characters.
“Seeholzer et al. showed a molecular divergence estimate of 1.4%
(using two mtDNA genes and a nuclear gene) between fitzpatricki and wallacei;
less than that between C. squamatus
and C. maculicoronatus (a sister
species pair from Trans-Andean South America/Panama that also share a similar
song to C. wallacei, both have
relatively small world ranges, and which differ from one another by 2.2%), and
considerably less than the divergence (4.9%) within C. auratus, a lowland species with wide distribution and large
population size. I suspect that effective population sizes may play a larger
role in the importance of these divergences, so that the rates themselves may
not really be comparable (as is basically suggested in Seeholzer et al.). In
this last case, I think the results of Armenta et al. (2005) will show that one
of Stiles’ arguments above for species status under the BSC is not quite right:
Armenta et al.’s results showed that Capito
auratus seems incapable of crossing the largest trunks of the
Amazon/Solimões drainage, distances considerably smaller than the ca. 400 km
separating C. wallacei from fitzpatricki. These are not what I would
consider “strong fliers” by any means, certainly not when compared to other
canopy species! Furthermore, the results of Armenta et al. (2005) also
suggested that carotenoid-based plumage variation does not stop introgression
among populations of Capito auratus,
because red- and orange-throated populations were not separable based on the
mitochondrial genes they used, suggesting that they introgressed freely where
they came into contact without geographic barriers (not surprising, as there
are specimens of intermediate plumage to corroborate this). Interestingly,
where barriers (large Amazonian rivers) occurred, populations on opposite sides
that looked identical (and have been historically considered members of the
same subspecies!) showed no recent gene flow. Returning to the C. maculicoronatus/squamatus clade, perhaps more comparable to the wallacei/fitzpatricki group in having smaller distributions, the two former
taxa differ from one another not in the saturation of carotenoid pigments so
much as in their placement, as well as considerably greater differences in
melanin pigment patterns, which I suspect may require more divergence time to
happen. That their divergence value is greater (again,
their population sizes must be larger, as well), I think demonstrates that they
are considerably farther along their independent evolutionary trajectories than
are wallacei and fitzpatricki. To make comparisons of the wallacei/fitzpatricki
complex to other members of Capitonidae seems to me to be the only path we can
take presently in trying to make sense of their taxonomic ranking with respect
to one another under the BSC. In conclusion, I would be inclined to rank fitzpatricki as a subspecies of C. wallacei under the BSC, but again
reaffirm that fitzpatricki is clearly
a species by the PSC.
“Literature cited
Armenta, J. K., J. D. Weckstein, and D. F.
Lane. 2005. Geographic variation in mitochondrial DNA sequences of an
Amazonian nonpasserine: The Black-spotted Barbet complex. Condor
107:527–536.”
Comments from Jaramillo: “YES – I find barbets and toucans troubling. Plumage coloration and voice sometimes tell different stories in these groups, and it confuses me. Various woodpeckers are in this camp too. In this particular case it boils down to a question of personal opinion, it becomes a subjective call. I am comfortable with calling this a new species, and hope that further work gains more data that confirms that this is a good choice.”
Comments from
Nores: “NO. It seems to me a subspecies of C. wallacei, for three reasons: 1) The
color patterns of the two species are very similar; only on the flanks
and lower chest the yellow color is replaced by red, a similar difference to
that between Capito niger punctatus and C. n. aurantiicinctus. 2) They are
alloptaric, despite the short distance between their ranges. 3) The average P-distance (1.14%) is small for
species.”
Comments from Robbins: “YES. I
could go either way on the treatment of fitzpatricki
as a species. Clearly, based on both plumage and limited genetic data these two
barbets are in the early stages of speciation, and unless there are dramatic
differences in vocalizations (doubtful), I suspect there would be gene flow if
they came together. However, given
that it was published as a species and there are no strong data to refute that
treatment (yes, it is a subjective decision), I’ll support species designation
for now.”