Proposal (1080) to South
American Classification Committee
Species limits in Myrmotherula
menetriesii: A. Treat the cinereiventris subspecies group as separate
species from M. menetriesii; B. Treat the subspecies omissa as
separate species from M. menetriesii; and C. Establish English names for
the three species.
Background: Our current
classification treats this group as consisting of a single species. The current SACC note is as follows:
26b. Isler et al. (2025)
provided rationale for treatment of this species as three separate species: (a)
M. menetriesii, including subspecies berlepschi, of southwestern
Amazonia, (b) M. cinereiventris, including subspecies pallida, of
northern Amazonia, and (c) M. omissa of southeastern Amazonia. SACC proposal badly
needed.
New
information:
Isler et al. (2025) analyzed vocal differences with respect to four types of
vocalizations as well as plumage color differences from throughout the
distribution of M. longipennis, with samples from all named
populations. In a companion paper,
Chesser et al. (2025) analyzed genetic differences from throughout the range.
Sampling
units
They
grouped their samples according to the boundaries of the described subspecies
in the map below. An additional partition was used in the analyses: western and
eastern populations of pallida and omissa because these formed
separate genetic clades in Chesser et al. (2025).
Vocalizations
Isler
et al. (2025) assembled a library of 490 recordings of Myrmotherula menetriesii
to analyze geographic variation in of four separate vocalizations (song and
three call types) the species geographic range. Here is a snip from their Methods:
“Criteria for diagnosability of vocal characters followed methods
developed in an earlier study (Isler et al. 1998). For quantitative characters,
we required the absence of range overlap and the likelihood of non-overlap with
larger sample sizes. For qualitative characters, such as note shape, we
required consistent visual diagnosability as determined in blind tests. We
employed quantitative and qualitative characters for songs, but only
qualitative characters for calls. We identified quantitative song characters in
stages. In the initial stage, we plotted the locations of recordings on digital
maps, and we selected three recordings of songs from different parts of each
study population’s geographic range on the basis of recording quality. We
obtained twenty-six measurements from spectrograms of songs and computed 19
ratios (e.g., first note length/terminal note length) from these measurements.
We obtained measurements from spectrograms projected on a 43-cm screen with the
default settings of RAVEN Pro 1.4 (Charif et al. 2010), except that the display
was set to smooth, overlap was adjusted from 50 to 93.7% depending on the
recording’s quality, and contrast was adjusted according to the recording’s
intensity, with care taken to retain all elements of the vocalization.
And:
“We then expanded the analysis to include all available and usable
recordings (except that we sampled randomly from locations for which there were
20 or more) and again eliminated characters whose ranges of measurements overlapped
among all pairs of study populations (except in rare instances in large samples
where extraordinary values were considered anomalies).”
Then,
they analyzed the recordings to search for and test for diagnosable characters
– see their paper for details.
For
loudsongs, they found two major song types that corresponded to (1) nominate mentriesii
+ berlepschi, and (2) cinereiventris. Some songs of berlepschi
could not be distinguished from some songs of the omissa group despite
there being strong average differences between the two.
Examples:
•
cinereiventris: https://xeno-canto.org/1031429 (by Richard
Webster)
•
omissa: https://xeno-canto.org/39148 (by Andrew
Spencer)
They
found that the Long Calls differed diagnostically among all three major clades;
see the figures in the paper for sonograms:
“Long Calls included two types of notes, abrupt notes and longer
downslurred notes. Superclades differed diagnostically in the sequence of the
two note types. Notes in Long Calls of the menetriesii superclade (n =
27) were limited to abrupt notes (Fig. 7A). In the cinereiventris
superclade (n = 55), the series of abrupt notes was preceded by a downslurred
note, and in about half of our sample the abrupt notes were followed by a
downslurred note (Fig. 7B); in rare instances downslurred notes were doubled.
In the omissa superclade (n = 32), the series of abrupt notes was
followed by downslurred notes (Fig. 7C), most often consisting of three notes
but sometimes fewer or more; shapes of downslurred notes varied among
individuals from narrow band width and dropping slightly in pitch to wider band
width and substantial pitch drop.”
Plumage
color
Isler
et al. (2025) examined 93 males and 84 females that included multiple samples
from all the taxa. For males, they
confirmed that the solid black throat and upper chest of the menetriesii
group is diagnostic for that group. For females, they found that:
“coloration of berlepschi was most distinct with olive-brown upperparts
and brownish-yellow underparts. Brownish yellow underparts were also
characteristic of omissa-E and omissa-W, but these populations
had upperparts gray tinged-olive as did the remaining populations (cinereiventris,
pallida, and menetriesii), whose underparts were shades of yellow
ochre. Within this general description, populations varied in darkness and
color mix (e.g., extent of olive in upperparts, extent of yellow in
underparts).:
Using
spectrophotometry on females, they found that discriminate function analysis
classified 90% of specimens correctly to population. They suspected that the
misclassified specimens could be young birds because a smaller study by Luciano
using specimens with skull officiation data found that the only two
misclassified specimens had partly unossified skulls.
Genetic
data
Chesser
et al. (2025) used DNA sequence data (ND2 and ND3 mitochondrial genes) to
construct the following phylogenetic hypothesis:
Of
interest to me is that one might predict from vocalizations, plumage, and
biogeography that the oldest split would have been between the cinereiventris
group north of the Amazon and everything else south of the Amazon, but there is
weak support for omissa and the cinereiventris group as sisters.
Given that this is mtDNA and that the support for the omissa-cinereiventris
node is very weak, I predict that broader gene sampling will falsify this.
PARTS
A and B
Taxonomic
Recommendations
Isler
et al. (2025) used the following rational for ranking taxa as species or
subspecies:
“We recommended species status under the Biological Species Concept for
populations that differed diagnostically in vocalizations (Johnson et al.
1999). Based on a study of vocalizations of syntopic, congeneric species-pairs
of antbirds (Isler et al. 1998) and subsequent applications, vocal differences
were considered diagnostic at the species level if three or more independent
vocal characters were identified. A finding of three distinct characters was
not viewed as a requirement but a guideline, however, and two vocal characters
were considered acceptable for populations that were clearly differentiated by
plumage based on spectrophotometric measurements or on distinct plumage
features. Plumage descriptions in taxonomic recommendations include currently recognized
characters. Study populations that differed in one or two characters and did
not meet requirements for recommendation as species were classified as
subspecies.”
Implementing
these criteria, they recommend the following three-species revision:
Myrmotherula menetriesii, including
also berlepschi as a subspecies
Myrmotherula cinereiventris, including also
pallida as a subspecies.
Myrmotherula omissa
Discussion
and recommendation: Iser et al. integrated data from vocalizations, plumage,
and mtDNA lineages to produce their recommended classification (and also provided
useful diagnoses for all taxa; their synopses under each taxon are
exceptionally useful and should set the standard for such publicarions). For
me, the radical song differences alone between north bank cinereiventris
and south bank menetriesii and omissa are sufficient and
necessary conditions for treating cinereiventris (with pallida)
to separate species rank. So, I recommend a YES on Part A.
As
for Part B, treating omissa as a different species, I am less certain,
and I will wait to see what others say. The case rests on diagnostic
differences between the Long Calls of omissa that distinguish it from
either menetriesii or cinereiventris. Also, it was the existence
of several intermediate songs in berlepschi and omissa (“because some examples of Songs in berlepschi
and omissa were intermediate in pace and frequency change”) that kept
those omissa and the menetriesii group from having diagnostic
differences in songs in addition to Long Calls.
Finally, there might be a contact zone between the two somewhere west of
the Rio Teles Pires in central Mato Grosso that would be worth studying, as
noted by Isler et al. On the other hand,
as can be seen in the tree above from Chesser et al, omissa is fairly strongly
differentiated genetically, at least in terms of % sequence divergence in mtDNA
(about 6%).
PART
C
English
names:
As in the previous proposal on the longipennis group, Isler
et al. recommended adding directional modifiers to the three species names as
follows: Northern Gray-Antwren, Western Gray-Antwren, and Eastern Gary-Antwren
(hyphens inserted by me). Although I
would normally ask for a separate proposal on English names, this is one of
those cases that I see no hope of improving on what Isler et al.
recommend. The plumage differences among
the females are slight, and the vocal differences don’t seem (to me) amenable
to descriptive names. There is a
conspicuous plumage difference between male cinereiventris and the other
two that makes a plumage-based name a possibility. Retaining “Gray” (itself a
pretty useless name in the realm of Myrmotherula) as a group name makes
these allospecies stand out as a unit amid the lengthy list of species called
Antwren, and the directional names, albeit duller than dirt, function to place
them in a geographic context. So, also vote on whether we should just go ahead
and adopt these names or wait for a separate proposal (that you are willing to
write) with inspired names. I also suspect that if there were more appealing
names out there, then that author team would have come up with them. (Cory
& Hellmayr 1924 is not of much help because omissa was not described
by then; they used “Gray-throated Ant Wren” for nominate cinereiventris
and “Western Gray-throated Ant Wren” for pallida, and the obvious
eponyms for menetriesii and berlepschi.)
For
voting purposes, a YES means you favor adopting the names proposed by Isler et
al., and a NO means that you favor some other option for which you are willing
to write a quick proposal if Part A (species limits) passes. If you vote NO on
Part A, you can either abstain or still vote either way on Part B.
References (if anyone
needs pdfs, just let me know):
CHESSER, R. T., M. L. ISLER, A.
SANTANA, E. K. LATCH, K. F. STRYJEWSKI, J. REED, L. NAKA, R. C. FLEISCHER, AND
A. ALEIXO. 2025. Comparative phylogeographic patterns in three
pan-Amazonian antwren lineages (Aves: Passeriformes: Thamnophilidae: Myrmotherula and Isleria). Zootaxa
5722: 1–44.
ISLER, M. L., R. T. CHESSER, K. F. STRYJEWSKI, AND B. M. WHITNEY. 2025.
Systematics of three pan-Amazonian antwren lineages (Aves:
Passeriformes: Thamnophilidae: Myrmotherula and Isleria). Zootaxa 5722: 45–78.
Van Remsen,
July 2026
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Vote tracking chart:
https://www.museum.lsu.edu/~Remsen/SACCPropChart1044+.htm