Proposal (446) to South American Classification Committee
Treat
Scytalopus opacus as a separate species from Scytalopus canus
Species Limits in the Paramo Tapaculo (Scytalopus canus)
Background:
The Paramo Tapaculo
(Scytalopus canus) is a common bird
inhabiting treeline scrub in the Northern Andes that ranges widely in the
Cordillera Central of the Colombian Andes and along the Ecuadorean Andes into
northern Peru, with additional populations in the Cordillera Occidental of
Colombia. The latter populations correspond to the nominate subspecies of S. canus, which was vocally unknown when
a comprehensive revision of species limits in tapaculos was conducted (Krabbe
and Schulenberg 1997). Therefore, such revision treated S. c. canus and S. c. opacus
(from the Cordillera Central, Ecuador and Peru) as conspecific pending
additional information.
New
Information:
Recent fieldwork in
the Paramo de Frontino area (Antioquia, Colombia) resulted in the first
recordings of S. canus canus and in
the collection of a specimen with tissue samples for genetic analyses. Songs,
calls, and mtDNA sequences of S. canus
canus have now been analyzed and compared to those of S. c. opacus from several localities (Krabbe and Cadena 2010); the
paper is available at this website:
http://evolvert.uniandes.edu.co/Biologia_Evolutiva_de_Vertebrados/Publications.html
The analyses show
that the song of S. canus canus is
sufficiently distinct from that of S. c.
opacus to consider these two forms as separate species in the context of
the criteria followed to establish species limits in Scytalopus over recent years. Also, the nominate subspecies of canus and subspecies opacus were shown to be more than 5%
divergent in mtDNA (ND2) sequences, which indicates a considerable period of
isolation.
Krabbe and Cadena
(2010) further showed that the populations of S. c. opacus occurring south of the Río Zamora in Ecuador and Peru
have very distinctive calls (but similar songs) in comparison to populations
occurring north of this river. Also, most males (10 of 12) from southern
populations exhibit a white patch on each wing. Further, phylogenetic analyses
suggested that northern and southern opacus
might not be each other's closest relatives, with the northern population being
more closely related to nominate S. canus
(a result supported strongly in some analyses but based on a single gene
and on sequences of only a handful of individuals).
In sum, Krabbe and
Cadena (2010) recommended splitting the Paramo Tapaculo in two separate species:
S. canus from the Cordillera
Occidental of Colombia and S. opacus
from the Cordillera Central of Colombia, Ecuador, and Peru. They further named
the southern Ecuadorian and Peruvian population as a new taxon, which they
treated as a subspecies of S. opacus
(S. o. androstictus). Although this
would seem to result in a paraphyletic S.
opacus because S. o. opacus
appears to be more closely related to S.
canus than to S. o. androstictus,
Krabbe and Cadena (2010) proposed this treatment considering (1) that
paraphyletic species are not at odds with the biological species concept (and
that inferences phylogenetic relationships might change as more genes and
individuals are considered) and (2) that calls have not been shown to function
as mechanisms of reproductive isolation in these birds, except perhaps for
examples in Brazilian taxa (see discussion under SACC proposal 329).
Recommendation:
For the reasons we
described in the paper and that I have summarized here, I recommend voting YES
to treat S. canus (Paramillo
Tapaculo) and S. opacus (Paramo
Tapaculo) as separate species - see rationale for English names in Krabbe and
Cadena (2010).
I realize that the
situation involving S. o. androstictus
merits some discussion, so perhaps committee members could comment on this as
well, and we can decide whether this proposal will suffice to accept the
treatment proposed in the paper or if it would be worth having a separate
proposal to split androstictus from opacus (I would personally maintain
these as conspecific pending more data).
Reference:
Krabbe, N., and C. D. Cadena, C.D. 2010. A
taxonomic revision of the Paramo Tapaculo Scytalopus canus Chapman
(Aves: Rhinocryptidae), with description of a new subspecies from Ecuador and
Peru. Zootaxa 2354, 56-66.
C. D. Cadena, July 2010
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Comments from Stotz:
“YES. Given the rampant increase in Scytalopus diversity, this split fits in
well with what we know about the genus. The
situation with androstictus is
definitely suggestive but like Daniel I’d like to see more data, and certainly
a separate proposal.”