Proposal (752) to South
American Classification Committee
Split Sclerurus
mexicanus into multiple species
The following proposal is a set of hierarchical taxonomic schemes for
the Sclerurus mexicanus complex. It
expands upon Proposal 603 with newly published vocal analyses (Cooper &
Cuervo 2017). This proposal is meant to be considered sequentially (i.e., Part
I must be approved to consider Part II).
Part I
Split Sclerurus mexicanus into two species: Sclerurus mexicanus and Sclerurus
obscurior.
Effect on SACC: Sclerurus
mexicanus would be split into two species that are assumed to be parapatric
in the DariŽn Gap. All known South American populations would become S. obscurior; S. mexicanus would be moved to the hypothetical list.
Background: The genus Sclerurus currently
contains six widespread, polytypic species. Sclerurus
mexicanus has the broadest distribution of any Sclerurus, with seven subspecies occurring from northern Mexico to
southern Brazil (Cooper and Barragan 2017; Fig. 1). Despite the recognized
diversity and broad distribution, differences are minimal (Remsen 2003) and
subspecies distributions are still incompletely known (Cooper and Barragan
2016; Cooper and Cuervo 2017). dÕHorta et al. (2013) found that Sclerurus mexicanus is not monophyletic
as currently defined. Rather, three major clades were discovered that form a
polytomy in the rufous-throated leaftosser clade: (1) S. mexicanus (subspecies mexicanus
and pullus) in North America; (2)
S. rufigularis; and (3) S. mexicanus (subspecies obscurior, andinus, macconnelli, and
peruvianus) in South America.
Similarly, recent vocal analyses only found S.
rufigularis to be statistically diagnosable when analyses allowed for
multiple species within the S. mexicanus
complex (Cooper and Cuervo 2017).
Figure 1. A map of
subspecific distributions within Sclerurus
mexicanus. Points represent localities from which vocalizations were
sampled. Figure from Cooper and Cuervo (2017).
Within the S. mexicanus
group, North and South American populations appear wholly allopatric,
diagnosably monophyletic (dÕHorta et al. 2013), and vocally distinct (Cooper
and Cuervo 2017). Unless all rufous-throated leaftossers are considered a single
species (including S. rufigularis),
the most prudent decision is to split S.
mexicanus into two taxa with no known geographic overlap:
1.
Sclerurus mexicanus
(Sclater 1856). Suggested English name: Central American Leaftosser. Type
locality: Cordoba, Veracruz, Mexico. This species contains two subspecies: mexicanus (from northern Nicaragua north
to east Mexico) and pullus (from
northern Costa Rica south to southern Panama). This includes certus (Chubb 1919, from Guatemala),
which is considered a synonym of mexicanus
(Hellmayr 1925).
2.
Sclerurus obscurior
(Hartert 1901). Suggested English name: Dusky Leaftosser. Type locality: Lita,
Esmeralda, Ecuador (ca. 600m). This species contains five subspecies: obscurior (the Choco lowlands), andinus (the mid-montane Andes of
Colombia, Ecuador, and Venezuela), peruvianus
(the eastern foothills of the Andes and western Amazonia in Peru, Ecuador,
Colombia, and probably Brazil), macconnelli
(eastern Amazonia and the Guianan shield), and bahiae (the Atlantic Forest of Brazil).
Thus, if accepted, all confirmed populations in South America would
become subspecies of S. obscurior.
Part IIA
Split Sclerurus mexicanus into Sclerurus
mexicanus and Sclerurus pullus.
Effect on SACC: This would only become important if the population pullus is confirmed in Northern
Colombia. Sclerurus pullus is known
from adjacent eastern Panama. This would have no effect on the main SACC list
at the present time; S. mexicanus
would be removed from the hypothetical list and replaced with S. pullus.
Background: Sclerurus mexicanus
and Sclerurus obscurior have no known
regions of overlap, with no confirmed records of Sclerurus mexicanus (sensu Part I) in the SACC region. However,
given that S. mexicanus pullus occurs
in eastern Panama immediately adjacent to Colombia, it is possible that the
taxon will be found in the SACC area in the future. Despite limited vocal data,
differences were recovered between S. m.
mexicanus and S. m. pullus (Cooper
and Cuervo 2017) and populations are reciprocally monophyletic (dÕHorta et al.
2013). A split of these two taxa is therefore warranted. This will have no
effect at the present time on the SACC list, but will change any future records
of S. mexicanus from northern
Colombia to S. pullus, as follows:
Sclerurus pullus (Bangs 1902). Suggested
English name: Isthmian Leaftosser (thus altering S. mexicanus to Tawny-throated or Mexican Leaftosser). Type
locality: Boquete, Panama. Distributed from northern Costa Rica through the
DariŽn in Eastern Panama. This species may occur in the DariŽn and Urab‡
regions of Colombia, and may exist parapatrically with S. obscurior. This species includes the synonym anomalus (Bangs and Barbour 1922), which
has erroneously been synonymized with andinus
in the past (Peters 1951).
Part IIB
Split Sclerurus obscurior
into three species: Sclerurus obscurior,
Sclerurus andinus, and Sclerurus macconnelli.
Effect on SACC: Sclerurus
obscurior would become three allopatric species, with Sclerurus obscurior being retained by lowland Choco populations.
Andean populations would become Sclerurus
andinus, and Amazonian/Atlantic Forest populations would become Sclerurus macconnelli.
Background: dÕHorta et al. (2013) recovered multiple
monophyletic clades within South American S.
obscurior (sensu Part I). These groups correspond to all subspecies for
which genetic data were available (i.e. all subspecies except bahiae), with the shortest branch lengths
for the division between S. o. peruvianus
and S. o. macconnelli (Fig. 2).
Given this short branch length, it is reasonable to consider S. peruvianus and S. macconnelli conspecific (but see Part III below). Cooper and
Cuervo (2017) tested multiple different partitioning schemes on Sclerurus songs and found the highest
support for a similarly conservative partitioning scheme that splits obscurior and andinus but retains peruvianus,
macconnelli, and bahiae as a single polytypic species.
Figure 2. Species partitioning schemes tested for the S. mexicanus complex. Branch lengths are
not to scale, but are presented proportionally and the tree depicts
monophyletic assemblages recovered by dÕHorta et al. (2013). Colored lines,
labeled 1-5, represent groupings discussed in Cooper & Cuervo (2017); with
respect to this proposal, partition 2 corresponds to Part I, partition 4 to
Part II, and partition 5 to Part III. Figure from Cooper and Cuervo (2017).
Genetic data supports the split of andinus
from obscurior (dÕHorta et al
2013): ÒAlong the continuum of humid forests from the Choc— lowlands to the
slopes of the western Andes, two lineages appear segregated elevationally: S. obscurior, and S. andinus found locally from about 1000 m (often up to 2000 m).
The two lineages are potentially syntopic at an intermediate point of the
elevational and ecological gradient, where no obvious physical barrier is in
placeÉ the lowland Choc— (i.e. S.
obscurior) and the Andean foothill species (i.e. S. andinus)É[last] shared a common ancestor in the Early Pliocene,
between 3.6 and 6.0 MaÓ.
Based on these data, Part IIB therefore proposes elevation of S. andinus and S. macconnelli to species level. S. obscurior would then become a monotypic taxon restricted to the
Choco (with the suggested English name ÔDusky LeaftosserÕ). The descriptions
for these new taxa would be as follows:
1.
Sclerurus andinus
(Chapman 1914). Suggested English name: Andean Leaftosser. Type locality:
Buenavista, above Villavicencio, Colombia, on the E slope of the Eastern Andes
(ca. 1370 m). This subspecies resides in humid submontane forest in western
Venezuela (the main Andes and the Sierra de Perij‡), all three Andean ranges of
Colombia, and in Western Ecuador. Records from northeastern Ecuador and
southwestern Ecuador (El Oro) may refer to this taxon.
2.
Sclerurus macconnelli
(Chubb 1919). Suggested English name: Long-billed Leaftosser (as opposed to
Short-billed Leaftosser S. rufigularis
with which this species is sympatric; MacConnellÕs, Amazonian, or Guianan
Leaftosser [as in Cory & Hellmayr] are also possible English names). Type
locality: Ituribisci River, Guyana. This species would consist of three
subspecies: peruvianus of the eastern
foothills of the Andes and western Amazonia; macconnelli of central and eastern Amazonia and the Guianan shield;
and bahiae of the Atlantic Forest of
Brazil. Records from Cear‡, halfway between the distributions of macconnelli and bahiae, are best left unidentified at this time. While parapatry is
assumed between peruvianus and macconnelli, the contact zone is not
well known.
Part III
Split Sclerurus macconnelli
into two species: Sclerurus macconnelli
and Sclerurus peruvianus.
Effect on SACC: Amazonian populations of S. macconnelli would be split into two species, with peruvianus occupying the western basin
and Andean foothills and macconnelli
occupying the lower basin, the Guianan shield, and the Atlantic Forest.
Background: While defined vocal differences between S. macconnelli subspecies (sensu Part
IIB) were not recovered (Cooper & Cuervo 2017), dÕHorta et al. (2013)
recovered two monophyletic groups aligning to the described populations of peruvianus and macconnelli. Per dÕHorta et al. (2013): Ò... S. macconnelli and S.
peruvianus É are in close geographical proximity in southern Peru and
Bolivia but seem to occupy different elevations along the cis-Andean
foothillsÓ. The magnitude of the differentiation between macconnelli and peruvianus
is less than any other branching event within S. mexicanus sensu lato, including the relationship between S. mexicanus and S. pullus.
Regrettably, no genetic data is presently available for bahiae, and its relationship to the rest
of the S. macconnelli complex is
uncertain. Thus, Part III opts for the elevation of S. peruvianus to species level while retaining bahiae as a subspecies of the geographically proximate S. macconnelli.
S. peruvianus (Chubb 1919). Suggested English name:
Peruvian Leaftosser (as in Cory & Hellmayr). Type locality: Yurimaguas,
Loreto, Peru. This species replaces macconnelli
in northwestern Amazonia and in the higher elevations of the Andean foothills
in southern Peru and Bolivia. Exact range limits are unknown, but it is known
to occur on both sides of the Napo/Amazon Rivers in Ecuador and Colombia.
Recommendation
Given the amount of genetic and vocal data available, we recommend the
acceptance of Part I and Part II (both A and B). Five species are repeatedly
delimited using both vocal and genetic data, and best represent the diversity
within S. mexicanus sensu lato. These
decisions would remove S. mexicanus
from the SACC list and replace it with three species: S. obscurior, S. andinus,
and S. macconnelli. One additional
species should be considered hypothetical within the SACC area (S. pullus) pending further surveys of
the DariŽn Gap.
Given the present data, we recommend holding off on Part III. The
relationship of bahiae to peruvianus and macconnelli is not resolved, and there is no reliable way to
identify these taxa in the field at the present time short of collecting
vouchers or genetic samples.
Literature
cited
Cooper,
J. C. & A. M. Cuervo. 2017. Vocal variation and species limits in the Sclerurus mexicanus complex. The Wilson Journal of Ornithology 129:13-24.
Cooper,
J. C. & Barrag‡n, D. 2017. Tawny-throated Leaftosser Sclerurus mexicanus. Neotropical Birds Online
<http://neotropical.birds.cornell.edu/>.
dÕHorta,
F. M., A. M. Cuervo, C. C. Ribas, R. T. Brumfield & C. Y. Miyaki. 2013.
Phylogeny and comparative phylogeography of Sclerurus
(Aves: Furnariidae) reveal constant and cryptic diversification in an old
radiation of rain forest understory specialists. Journal of Biogeography 40:37-49.
Other references in SACC bibliography.
Jacob
C. Cooper & Andres M. Cuervo, May 2017
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Comments from Jaramillo: ÒPart I Ð YES, data look solid to me, and include
multiple independent sets of data. Note that Central American Leaftosser does
not work for me.
ÒPart IIA Ð YES, assuming it
eventually is found in Colombia.
ÒPart IIB Ð YES, I find it
powerful that obscurior and andinus are syntopic, and replace each
other elevationally. It is unfortunate that bahiae
was not sampled molecularly, as it may shift the tree perhaps?
Part III Ð NO, unresolved as
noted in the proposal. Data needed for bahiae,
as well as no reliable way to identify taxa in field!Ó