Proposal (#363) to South American Classification
Committee
Split
Zimmerius chrysops into two or three species
Effect on South
American checklist: This would leave Zimmerius chrysops
and Z. viridiflavus as separate species, and split out two
additional species from chrysops, Z. albigularis and Z. flavidifrons.
Background:
The genus Zimmerius was erected by Traylor (1977) for a set of small
tyrannulets placed in the genus Tyranniscus, which lacked true wingbars
among other characters. There have been a number of taxonomic issues at the
species-level within the genus. In this case, the taxon Zimmerius chrysops has
been variously treated as a distinct species (Zimmer 1941, Ridgely and Tudor
1994, Ridgely and Greenfield 2001, Fitzpatrick et al 2004), or conspecific with
Z. viridiflavus (Meyer de Schauensee 1966, 1970, Schulenberg et al
2007). SACC has previously considered the issue of chrysops and viridiflavus
in Proposal 173, which
proposed lumping chrysops and viridiflavus. It did not pass, but
did engender extensive commentary relevant to the current proposal.
The voice of
Ecuadorian chrysops is distinct from Peruvian viridiflavus
(Ridgely and Tudor 1994). However, Schulenberg et al (2007) noted that birds
morphologically like chrysops that are found in Peru south of the Rio
Marañon sound like viridiflavus. The details of this mismatch between
voice and plumage were described in detail in Proposal 173 to relump Z.
chrysops and Z. viridiflavus. Further complicating the issue are flavidifrons
from southwestern Ecuador and northwestern Peru and albigularis from
western Ecuador and southwestern Colombia. These taxa look much like chrysops
but also have distinct voices.
Analysis and new
information: In Proposal 173, Dan Lane called for genetic
work on this complex. That genetic work has now been done. Rheindt et al.
(2008) examined pieces of mitochondrial (NADH) and nuclear DNA (Fibrinogen
intron 5) for the genus Zimmerius.
His trees find that albigularis
does not associate on the tree with chrysops or viridiflavus.
Instead, it is sister to Zimmerius vilissimus. The rest of the chrysops/viridiflavus
complex forms a clade that subdivides into two well-differentiated groups. One
group, their Clade 1 contains populations of chrysops from north of the
Rio Marañon. Their Clade 2 contains viridiflavus, chrysops from south of
the Marañon, and flavidifrons. These two clades have 100% bootstrap,
etc. support. Because they are sister to one another, this tree is consistent
with either lumping or splitting viridiflavus and chrysops. This
is also completely consistent with the vocal data described by Dan Lane in
Proposal 173.
Recommendation:
Proposal A. Treat Zimmerius
albigularis as a separate species. I recommend a YES
vote, Rheindt et al (2008) started with this change, because it is most
strongly supported by the genetic work. Given that this taxon has a distinct
voice from the members of the viridiflavus complex, and genetically is
not part of this complex, but rather more closely related to Zimmerius
vilissimus, this seems like an easy decision. Rheindt et al suggested an
English name of Choco Tyrannulet for albigularis, which seems like a
reasonable suggestion.
Proposal B. Treat Zimmerius
chrysops as conspecific with Z. viridiflavus.
I recommend a NO vote. SACC has already voted against this concept, and the
genetic data supports the basic idea that the two vocally distinct groups, chrysops
north of the Marañon, and viridiflavus plus chrysops from
south of the Marañón, along with flavidifrons are monophyletic units.
The definition of chrysops that we have been using based on morphology
is not supported by the vocal or genetic data. However, the vocal and genetic
data align very well, and the name chrysops is the correct one for the
northern taxon.
Proposal C. Treat Zimmerius
flavidifrons as a separate species. I recommend a YES
vote, weakly. Zimmerius flavidifrons should only be treated as a
distinct species, in my view, if chrysops and viridiflavus are
treated as separate species. If they are lumped, then flavidifrons is
genetically buried in the heart of that complex. Committee members should look
at Mark Robbins' comments on Proposal 173 for information on the vocalizations
of this taxon. Genetically and vocally, flavidifrons is associated with viridiflavus,
but its plumage resembles chrysops. The voice, while sharing
certain features with flavidifrons, is distinct, whereas genetically it
is sister to viridiflavus + south of the Marañon chrysops. Treating
it as a distinct species seems reasonable, but not a slam dunk. Rheindt et al.
suggested treating flavidifrons as a subspecies of viridiflavus. They
argued that although the voice is different, it is not very different from viridiflavus,
and that genetically it is not very different from viridiflavus,
<1% different, compared to ca. 7% difference between viridiflavus and
northern chrysops.
There are actually 3
potential treatments of this taxon. One is to raise it to a separate species.
One is to continue to treat it as a subspecies of chrysops. This would
match morphology, but be in conflict with genetics and voice. It is implicitly
our current treatment. The third treatment would be to lump it into viridiflavus.
This last treatment would make more sense if flavidifrons is not
considered a distinct species. It is the treatment recommended by Rheindt et
al. For flavidifrons, if split, Ridgely and Greenfield suggest the name
Loja Tyrannulet, which seems appropriate.
Rheindt et al also
suggested that if northern chrysops is split, and viridiflavus, southern
chrysops, and flavidifrons are treated as a single species, then
the name Peruvian Tyrannulet is not appropriate for viridiflavus. They
suggest Tschudi's Tyrannulet, which has a history of being applied to viridiflavus.
I am not sure I agree with them. However, if, when the dust settles, we have
created that taxon, then I will do a proposal for such a name change.
Further
recommendation: Because the SACC list is strictly at the
species level and we provide no geographic range for the species, the
assignment of intraspecific populations to particular species is not always
clear. Such is the case in this instance. If we recognize (as we currently do) chrysops
and viridiflavus as distinct, the treatment of the chrysops from
south of the Marañón and of flavidifrons is ambiguous. I think,
implicitly, we currently follow the treatment of taxa and populations suggested
by Ridgely and Tudor (and followed by Howard and Moore), in which flavidifrons
and all of chrysops are included in chrysops.
A more reasonable
treatment would be to continue to recognize two species, but include the
southern populations of "chrysops" in viridiflavus
along with flavidifrons (the suggested treatment of Rheindt et al). However,
vote of No on both Proposals B and C do not distinguish between the two
alternatives. So I would like to ask that committee members that vote No on
Proposal B specify whether they accept the Rheindt tree which places southern chrysops
with viridiflavus and flavidifrons or are maintaining the
status quo of all of chrysops together. Similarly, if committee members
vote No on Proposal C, they should indicate whether they want to associate flavidifrons
with chrysops or with viridiflavus. I would recommend
associating it with viridiflavus. I would hope that we can then include
the information on the assignment of these populations by the committee in the
notes online, assuming that one or the other of these votes require this
specification.
One additional issue
with respect to the placement of populations within the named species is that
Rheindt et al in their suggested treatment (table 5 in the paper) treat the
southern populations of chrysops as part of their subspecies flavidifrons.
This doesn't seem to match the genetics, voice or plumage.
One final note. The
population of "chrysops" from south of the Marañón appears to
have no name. If this group is split off from the northern chrysops and
not considered part of flavidifrons, it will require a subspecific name.
References:
FITZPATRICK, J. W.
2004. Tyrannidae. Pp. 170-462 in "Handbook of the Birds of the
World, Vol. 9. Cotingas to pipits and wagtails." (J. del Hoyo et al.,
eds.). Lynx Edicions, Barcelona.
MEYER DE SCHAUENSEE,
R. 1966. The species of birds of South America and their distribution.
Livingston Publishing Co., Narberth, Pennsylvania.
MEYER DE SCHAUENSEE,
R. 1970. A guide to the birds of South America. Livingston Publishing Co.,
Wynnewood, Pennsylvania.
RHEINDT, F. E., J. A.
NORMAN, AND L. CHRISTIDIS. 2008. DNA evidence shows vocalizations to be better
indicator of taxonomic limits than plumage patterns in Zimmerius
tyrant-flycatchers. Molecular Evolution and Phylogenetics 48:150-156.
RIDGELY, R. S., AND
P. J. GREENFIELD. 2001. The birds of Ecuador. Vol. I. Status, distribution, and
taxonomy. Cornell University Press, Ithaca, New York.
RIDGELY, R. S., AND
G. TUDOR. 1994. The birds of South America, vol. 2. Univ. Texas Press, Austin.
TRAYLOR, M. A., JR.
1977. A classification of the tyrant-flycatchers (Tyrannidae). Bulletin, Museum
of Comparative Zoology 148:128-184.
ZIMMER, J. 1941.
Studies of Peruvian birds, No. 37. The genera Sublegatus, Phaeomyias,
Camptostoma, Xanthomyias, Phyllomyias and Tyrannus. American
Museum Novitates 1109: 1-25.
Doug Stotz, July 2008
__________________________________________________________________________________________________________________
Comments
from Stiles:
"363A. YES.
Genetic and vocal data (plus my limited experience with
albigularis
in SW Colombia) support this change.
363B. NO. Again, two
species-level taxa are supported by both genetic and vocal data.
363C. NO,
tentatively. This one is harder, since flavidifrons is much ore closely
associated with viridiflavus both genetically and vocally. On present
evidence, it might be best to retain flavidifrons as a distinctive
subspecies of viridiflavus (with consequent naming of the S-of-Marañón chrysops
as a third subspecies - actually, this must be done in any case. I am reluctant
to split flavidifrons as a species at the present time - there are
several other such cases of vocally (but not, or barely, in plumage)
distinctive subspecies in tyrannid species like "Myiozetetes similis"
and "Tolmomyias sulphurescens" that need genetic work. When
this is done, we will have a better "yardstick" to judge such cases.
For now, I favor a conservative approach."
Comments from Robbins:
"Doug has done a good job of summarizing this complicated group.
"363A. I vote
"YES" for recognizing albigularis
as a species, as both genetic and vocal data support this.
"363B. I vote
"NO" for considering chrysops and viridiflavus as
conspecific, as genetic and vocal data indicate that they should be considered
species.
"363C. I vote
"YES" in recognizing these as species, because the voice of flavidifrons
appears quite distinct from viridiflavus (see my comments in proposal
173) and they differ in plumage morphology."
Comments
from Schulenberg:
"363A
(treat Zimmerius albigularis [no subtle guiding of our votes there] as a
separate species): YES.
"363B NO. I'm
thinking here only of "true" (northern) chrysops; the southern
chrysops I would place with viridiflavus.
"363C: YES. This
is complicated, but I think it's the right approach. I would leave no-name chrysops
("chrysops" in northern Peru south of the Maranon) in with viridiflavus,
which of course is what it sounds like."
Comments
from Nores: "
"A. YES. Como señala Stotz resulta una fácil decisión, ya que
tanto por la voz como genéticamente se separa totalmente de chrysops.
"B. NO. Genéticamente hay dos grupos de chrysops bien
separados: el de Ecuador y norte de Perú (chrysops) y el del sur de Perú
(viridiflavus).
"C. NO. Genéticamente y por vocalizaciones está relacionado con viridiflavus
y no debería ser separado como especie. Aunque por coloración se parece a chrysops
esto no parece tener mayor importancia, ya que como señalan Rheindt et al. las
vocalizaciones resultan mejor indicador de especie que la coloración en este
grupo de tiránidos. Aunque esta opinión va en contra de mi modo de pensar como
taxónomo, los análisis moleculares indican que los criterios usados en la
taxonomía clásica no siempre son correctos."
Additional comments
from Frank Rheindt:
"In his well-summarized
proposal to carry out taxonomic splits within the Zimmerius chrysops
complex, Dr. Stotz referred to our recent paper (Rheindt et al. 2008. MPE 48:
150), in which we advocated the elevation to species rank of albigularis
and called for a transfer of flavidifrons and "southern chrysops"
to Z. viridiflavus. All SACC committee members who have so far cast
their verdict have agreed with the albigularis split and the transfer of
"southern chrysops" to Z. viridiflavus, but some have
argued that the Tumbesian taxon flavidifrons should also be elevated to
species rank rather than be lumped with Z. viridiflavus.
"In response, I would like
to draw attention to the disappointingly small sample size of our cited study.
The Zimmerius paper was the fortuitous side product of a PhD thesis that
primarily focused on another tyrannid genus, so a more thorough sampling regime
was not feasible. The geographical sampling did not do full justice to the
interesting phylogenetic patterns within the Zimmerius chrysops complex,
and I hope the publication of these preliminary results will not dishearten
other researchers from revisiting this genus with a more thorough sampling
regime.
"While increased sampling is
unlikely to change conclusions with regard to the solid albigularis
split and the transfer of "southern chrysops" to Z.
viridiflavus, much more geographical sampling is required to evaluate the
final status of flavidifrons under the biological species concept. We
advocated a subsumption of flavidifrons under Z. viridiflavus
mainly based on the small mtDNA divergence (1%) that falls much below the
typical level of divergences between tyrannid sister species. Since many SACC
committee members may be reluctant to accept genetic divergences as guidance in
taxonomic decisions where there is little comparative material from closely
related taxa, it is worth noting that there are now a few studies that place
this divergence in a comparative framework and that have consistently
documented mtDNA divergences in excess of 4% in a wide range of tyrannid sister
species pairs, including closely related elaeniine genera (e.g. Johnson &
Cicero, 2002, Mol Ecol 11: 2065; Joseph et al, 2003, MPE 31: 139; Chesser,
2000, MPE 15: 369; Rheindt et al, 2008, BMC Evol Biol 8: 193; Rheindt et al,
2008, Emu 108: 261). The divergence between Z. chrysops (sensu our
study) and expanded Z. viridiflavus is 7%!
"Those who prefer to
discount the low mtDNA divergence as a yardstick may want to consider that the
morphological and vocal cases for species status are not that strong either:
(1) The most
pronounced break in plumage pattern does not fall between flavidifrons
and the east-slope taxa, but within the east-slope taxa (i.e. between unnamed
"southern chrysops" and viridiflavus); a flavidifrons
split on morphological grounds would therefore have to include a transfer of
"southern chrysops" to flavidifrons, which would
counter-argue vocal data.
(2) There is much disagreement
over just how different flavidifrons vocalizations are, and whether
these differences merit biological species status; see the excellent discussion
in SACC Proposal 173 between people with some of the most field experience in
this genus. Some argue that the break of the single flavidifrons call
into 2-3 vocal elements within the east-slope taxa is substantial enough to
prevent them from interbreeding in hypothetical non-allopatric settings.
However, the ranges of these taxa may not be allopatric at all, as they closely
approach each other in the Maranon Gap. Vocal and genetic sampling in this
region may show intermediacy in call types/repertoire and mtDNA, which would
argue for a cline rather than distinct species. Even in the absence of a
continuous range, vocal and genetic characters may approach each other where flavidifrons
comes close to the Maranon. I guess a particularly interesting area to sample
would be the Zumba/Palanda region of Zamora-Chinchipe Province in Ecuador and
neighboring parts of Peruvian Cajamarca (San Ignacio down to the Maranon Gap).
Maybe some SACC members or other field workers already have access to
recordings or even genetic data from this area? In any case, I think more
thorough vocal and/or genetic sampling from this region should be carried out
before separating flavidifrons at the biological species level."
Comments
from Jaramillo:
"A - YES
B - NO
C - YES. This is the
most problematic of the choices. Voice and genetic work show it is a distinct,
albeit relatively young lineage. It seems to me that the cleanest thing to do
is separate it as a species for the reasons Stotz outlines."
Comments
from Cadena:
"A: YES
B: NO
C: NO. I think more
work is necessary to define species limits in the viridiflavus group
before species status can be assigned to flavidifrons. In relation to F.
Rheindt's comments, he mentions that committee members who had voted thus far
had accepted "the transfer of southern chrysops to viridiflavus".
Because southern chrysops does not (yet?) have species rank, this is
something that would not be reflected in our classification, but I just thought
I'd should note we are actually not voting for this in the current proposal, or
am I missing something? Also, just for the record: although Rheindt et al.
(2008) did look at variation in a nuclear gene, this was not informative about
relationships in the clade, so their molecular phylogeny is based entirely on mtDNA."
Comments
from Pacheco:
"A YES
B NO
C NO. Sobretudo por conta da opinião emanada pelo Daniel,
prefiro ser conservador neste item e aguardar por novos estudos."