Proposal (1039) to South American Classification Committee
Split Camptostoma
obsoletum into six species
Background:
Camptostoma
obsoletum
currently comprises 13 subspecies taxa distributed across Central and South
America, from Costa Rica to Uruguay. Fragmentary vocal and genetic evidence
suggests that it may include multiple biological species (Ridgely and Tudor 1994, Ridgely and Greenfield 2001,
Rheindt et al. 2008). However, current taxonomy remains entirely based
on subtle variations in plumage and morphology, which are unlikely to reflect
true species limits in this group (Fitzpatrick 2004).
New
Information:
A
newly published analysis of geographic vocal variation in the genus Camptostoma,
based on 1,113 recordings of vocalizations from 994 individuals across 783
localities, identified six vocally distinct populations within C. obsoletum
(Lima and Vaz 2024). These
populations exhibit diagnostic differences in multiple different vocalization
types, including vocalizations that are typically species-specific in the
Tyrannidae. The populations are mostly allopatric but have abutting
ranges over large areas, with little evidence of gene
flow between them (Lima and Vaz 2024).
Assuming that the several diagnostic differences in multiple
vocalization types have the potential to generate substantial premating
isolation among these vocally distinct populations, and considering the
apparent pattern of parapatry without gene flow between several of these
populations, Lima and Vaz (2024) proposed splitting C. obsoletum into six
biological species, maintaining vocally undifferentiated taxa with potential
plumage differences as subspecies pending further study:
· Camptostoma
flaviventre Sclater & Salvin, 1865
o
C. f. flaviventre Sclater
& Salvin, 1865
o
C. f. majus Griscom, 1932
o
C. f. orphnum Wetmore, 1957
· Camptostoma
caucae Chapman, 1914
· Camptostoma
pusillum (Cabanis & Heine, 1860)
· Camptostoma
sclateri (Berlepsch & Taczanowski, 1884)
o
C. s. sclateri (Berlepsch
& Taczanowski, 1884)
o
C. s. maranonicum Carriker,
1933
o
C. s. griseum Carriker, 1933
· Camptostoma
napaeum (Ridgway, 1888)
o
C. n. napaeum (Ridgway, 1888)
o
C. n. olivaceum
(Berlepsch, 1889)
· Camptostoma
obsoletum (Temminck, 1824)
o
C. o. obsoletum (Temminck,
1824)
o
C. o. cinerascens (Wied,
1831)
o
C. o. bolivianum Zimmer,
1941
Here’s a figure from Lima and Vaz (2024) illustrating the
geographic ranges of the proposed species based on the sound recordings
examined. For further details about the figure, including information about
extralimital taxa, see Lima and Vaz (2024).
The proposal is subdivided as follows:
A. Treat sclateri (including maranonicum and griseum)
as a separate species from C. obsoletum
Camptostoma o. sclateri differs diagnostically from all
other taxa except maranonicum and griseum in daytime and dawn
songs as well as multiple calls (Lima and Vaz 2024). Although field playback
experiments suggest weak behavioral discrimination between sclateri and napaeum
based on daytime songs (Freeman et al. 2022), no evidence of hybridization
exists despite potential parapatry (Lima and Vaz 2024). Other vocalizations may
mediate premating isolation, although this remains untested (Lima and Vaz
2024). Alternatively, sclateri and napaeum may form undetected,
narrow hybrid zones.
B. Treat pusillum as a separate species from C.
obsoletum
Camptostoma o. pusillum differs diagnostically from all
other taxa multiple vocalizations, including daytime and dawn songs (Lima and
Vaz 2024). There is no evidence of gene flow with adjacent populations (caucae
and napaeum), despite potential parapatry (Lima and Vaz 2024).
C. Treat caucae as a separate species from C. obsoletum
Camptostoma o. caucae differs diagnostically from all
other taxa in daytime and dawn songs and multiple calls (Lima and Vaz 2024). No
evidence of hybridization exists with the apparently parapatric pusillum
and napaeum, suggesting strong premating isolation (Lima and Vaz 2024).
D. Treat napaeum (including olivaceum) as a separate
species from C. obsoletum
Camptostoma o. napaeum differs diagnostically from all
other taxa but olivaceum in multiple vocalizations, including daytime
and dawn songs (Lima and Vaz 2024). While differences with parapatric obsoletum
are subtle, and some hybridization may occur, phenotypic distinctiveness
despite extensive contact (~3,300 km) suggests substantial—albeit
incomplete—reproductive isolation (Lima and Vaz 2024).
E. Treat flaviventre (including majus and orphnum)
as a separate species from C. obsoletum
Camptostoma o. flaviventre, C. o. majus, and C. o.
orphnum collectively form a vocally unique population, differing
diagnostically from all others in multiple vocalizations (Lima and Vaz 2024).
Although this population occurs only in Central America based on the sound
recordings examined by Lima and Vaz (2024), I included it here in the proposal
because it may plausibly occur in extreme western Colombia near Panama. I defer
to the committee to determine whether South American records exist.
References:
Fitzpatrick,
J. W. (2004). Family Tyrannidae (Tyrant-flycatchers). In Handbook of the
Birds of the World (J. del Hoyo, A. Elliott and D. Christie, Editors). Lynx
Edicions, pp. 170–462.
Freeman, B.
G., J. Rolland, G. A. Montgomery, and D. Schluter (2022). Faster evolution of a
premating reproductive barrier is not associated with faster speciation rates
in New World passerine birds. Proceedings of the Royal Society B
289:20211514.
Lima, R.
D., and R. V. Vaz (2024). Divergence in vocalizations indicates cryptic
speciation in Camptostoma tyrannulets. Ornithology: ukae058[RL1] .
Rheindt, F.
E., J. A. Norman, and L. Christidis (2008). Genetic differentiation across the
Andes in two pan-Neotropical tyrant-flycatcher species. Emu 108:261–268.
Ridgely, R.
S., and P. J. Greenfield (2001). The birds of Ecuador: status, distribution,
and taxonomy. Cornell University Press.
Ridgely, R.
S., and G. Tudor (1994). The birds of South America. Volume 2 (The Suboscine
Passerines). University of Texas Press.
Rafael D. Lima, December
2024
Note
from Remsen on English names: A separate proposal on English names will be
needed if any of these proposals passes.
___________________________________________________________________________________________________
Comments
from Lane:
“YES. Regardless of whether there is a molecular component to this study, I
applaud the authors’ efforts to break down a potential headache of a complex,
and I see this study as good enough to act upon here. I agree with their
assessments of the taxa, the vocal groupings, and their outlining of daughter
species. YES to all proposed splits from C. obsoletum.”
Comments
from Zimmer:
“YES to all splits (see separate subproposals below) as advocated in the
Proposal, and as suggested by Lima & Vaz 2024. I have long grappled to make sense of what I
was perceiving as vocal distinctions within the C. obsoletum group
across its broad range, and have it mesh with plumage differences and
understood distributions of named taxa, but without the kind of geographically
broad-based and well-sampled vocal analysis conducted by Lima & Vaz (2024),
it has remained a muddled mess in my mind.
Part of the confusion is due to the effects of wear and fading on some
of the few plumage characters that can actually allow visual discrimination of
taxa in the field, and part of it is due to each population having multiple
types of vocalizations in their repertoires (songs, dawn songs, contact calls,
agitation/interaction calls, etc), and without a systematic, thorough analysis,
you can’t be sure that you are always comparing apples to apples and oranges to
oranges. The absence of a molecular
component to this study does not bother me, since I believe vocal differences
in these phenotypically conserved groups of suboscines are almost always going
to provide the strongest indication of species-limits.
“A. Treat sclateri (including maranonicum
and griseum) as a separate species from C. obsoletum: YES, also matches my
field impressions of vocal distinctions.
“B. Treat pusillum as a
separate species from C. obsoletum: YES, also matches my field
impressions of vocal distinctions.
“C. Treat caucae as a separate species
from C. obsoletum: YES, based upon vocal distinctions and no evidence of
hybridization with parapatric pusillum and napaeum, as detailed
in Lima and Vaz 2024.
“D. Treat napaeum (including olivaceum)
as a separate species from C. obsoletum. YES. This also matches my field impressions
of vocal distinctions.
“E. Treat flaviventre (including majus
and orphnum) as a separate species from C. obsoletum. YES. This one with
particular enthusiasm, based on my own field impressions in Panama/s Costa
Rica. I do not, however, have any
evidence for whether South American records of flaviventre exist.”