Proposal
(58) to South American Classification
Committee
Elevate
subgenus Megascops (New World Otus) to full generic status
Note: This proposal is a slightly modified version of the one
Carla Cicero submitted to AOU CLC (which voted to accept the proposal).
Comments on some New World taxa, especially O. flammeolus, have
been left in because they are of interest in evaluating the split of Otus.
Effect on SACC: This proposal would place all South American Otus in
the genus Megascops
The 2nd edition of the AOU Check-list (1895) recognized Megascops for
the Screech Owl and Flammulated Screech Owl, the only 2 species of Otus covered
by the CL at the time. These species were placed in Otus in
the 3rd edition (1910). All subsequent treatments by the AOU and other
authorities have continued to recognize Otus for New World +
Old World species, with Megascops as a synonym.
On the basis of vocal differences, Marshall and King (1988)
divided Otus into two main subgenera: Otus for Old
World (Old World) scops owls with slow notes; and Megascops for
New World (New World) screech owls with fast trills. They also recognized
several other subgenera, including: Ptilopsis for O.
leucotis (Old World); Pyrroglaux for O. podarginus (Old
World); Macabra for O. albogularis (New World); and Gymnasio
for O. nudipes and O. lawrencii (New World),
the latter also placed in the genus Gymnoglaux. Species in Pyrroglaux,
Macabra, and Gymnasio all lack erectile ear tufts, unlike other
members of the group. Of these New World subgenera, only Megascops and Gymnasio
occur in the Check-list Area.
In addition to temporal aspects of the song, New World and
Old World Otus also differ in having one vs. two fundamental
song types (König et al. 1999). With the exception of O. flammeolus,
New World species have two song types, including a primary song
("A-song") used for territoriality, and a secondary song
("B-song") used in courtship and male-female duetting; the
"A-song" typically consists of a long trill or sequence of single
notes in fairly rapid succession, while the "B-song" is relatively
short and often given in a characteristic rhythm. Old World species have only
one song type, which is never a long trill like that of New World species; this
song is used in both aggressive situations and in courtship during duets with
females. The Flammulated Owl (O. flammeolus) also utters a single song
type (not a trill) and thus is more similar bioaccoustically to Old World Otus
than to Megascops. Likewise, the Cuban Screech-owl (Gymnoglaux
lawrencii) also gives only a single song type. The Puerto Rican Screech-owl
gives two song types like other Megascops, although Marshall and
King (1988) placed it in the same subgenus (Gymnasio) as the Cuban
Screech-owl.
König et al. (1999) showed with cytochrome b sequences
(17 species) that New World and Old World Otus are strongly divergent
genetically, and suggested elevating Megascops to full genus
(although in their book, they maintain Otus with Megascops as
a synonym). In their analyses, members of Otus appear in at least three
different clades, making the genus polyphyletic: Ptilopsis forms
a clade with Asio otus, whereas Old World and New World Otus form
divergent monophyletic clades; all of these have strong bootstrap support. Old
World and New World Otus are separated by uncorrected genetic
distances of 12-16%, which is comparable to values between other genera of owls
that they examined.
On the basis of the genetic data plus vocal differences, I
propose that we treat Megascops as a full genus. This leaves
two remaining questions, however, i.e., how to treat O. flammeolus and O.
nudipes. Marshall and King (1988), König et al. (1999), and Hoyo et al.
(1999) all leave flammeolus within Otus, making it the only New
World species belonging to the Otus assemblage referred to as
subgenus Otus (Hoyo et al. 1999). This treatment is based primarily on
the vocal similarity to Old World Otus. Unfortunately, the genetic data
are inconclusive re: the relationship of O. flammeolus. Cytochrome b sequences
(König et al. 1999) place this species as basal to the clade of New World Otus,
but with bootstrap support < 50% (see Fig. 55b). Average uncorrected
sequence divergences for various interspecific comparisons are as follows:
within New World Otus, excluding O. flammeolus, 10.1%;
within Old World Otus, 9.8%; Old World vs. New World Otus (excluding O.
flammeolus), 15.1%; O. flammeolus vs. other New World
species, 14.5%; O. flammeolus vs. Old World Otus,
16.4%. Although the Flammulated Owl is slightly less divergent from New World
species, it appears to be highly divergent from both Old World and New World
taxa. Furthermore, divergences within the subgenera are also quite high. Thus,
additional genetic data are needed to resolve the placement of O. flammeolus
relative to New World and Old World Otus. In the meantime, I
propose that we maintain flammeolus in Otus, on the basis of
vocal data and also because this is the most conservative treatment. If flammeolus is
indeed “basal" to New World species (needs to be corroborated by other
data), only a single synapomorphic change is needed to account for the
different song type(s) seen in New World species.
Carla Cicero, August 2003
Comments from Remsen: I vote YES on this proposal for
reasons outlined above. I suspect that "Otus" is really just a
"morphotype" of smallish owls that will prove polyphyletic with
additional sampling and use of nuclear genes. Unlike Bubo, Strix,
and Asio, with boreal and arctic species that make a Holarctic
distribution "sensible", Otus is much more tropical,
making, in my opinion, parallel/convergent evolution as likely an explanation
for their similarity as a deep, ancient, pantropical split or a
dispersal-launched colonization of one hemisphere or the other (by
migratory O. scops/O. surnia/O. flammeolus stock?). So, I like
keeping the groups in separate genera at least until they can be shown to form
a monophyletic group.
Comments from Stiles: "Having read the Megascops proposal,
I think the evidence is good as far as it goes, though clearly more work is
needed on these beasties. So, YES (as far as it goes)!"
Comments from Schulenberg: "My vote is No. The proposal
repeatedly refers to the work of "König et al. (1999)". I assume that
in fact what is meant is the separately authored piece (Michael Wink and Petra
Heidrich) that is included in (but not authored by) König et al. 1999,
"Owls: a guide to the owls of the world". What this would seem to
imply, among other things, is that the chapter by Wink and Heidrich was not
peer-reviewed. Of course, peer review, like a PhD degree, isn't all that it's
assumed to be, and like a PhD degree, is no guarantee of much of anything. But,
had I had the chance to review this manuscript prior to publication, I would
have given it a hard time. For starters, I see that they like to use
neighbor-joining (NJ) analyses. I know that there are computer simulation
studies that suggest that, at least under some condition, NJ does more or less
as well as other types of analyses, such as maximum parsimony. But I also have
the feeling that NJ is what a lab group reaches for when they want a tree (any
tree), and are less interesting in exploring what their data really are telling
them. So, my suspicions are aroused right off the bat whenever I see NJ used.
"Speaking of exploring what their data are telling
them, there is no indication here that they looked at how many nucleotide
substitutions they had overall, how these were distributed (by codon,
transversions vs. transitions) and what parts, if any, of their dataset were
"saturated" and so were useless for their purposes. Speaking of
saturation, when one gets into very large genetic distances, saturation is hard
to avoid. Their distance matrix is loaded with values of over 10% (in some cases
well over 10%). For cytochrome b, I find it difficult to imagine that they have
any useful data with those kind of distances. "So, in sum, I really don't
care what kind of bootstrap support they have. What little I know about
cytochrome b and "deep" splits tells me that the gene simply can't be
used to resolve such relatively ancient branching patterns, such as near the
base of tree (which, with respect to clades of screech/scops-owls, is what we
are interested in here). And these authors did absolutely nothing to convince
me otherwise.
"It wouldn't surprise me at all that New World Otus are
a monophyletic or largely monophyletic (apart from flammeolus)
group with respect to Old World Otus. Whether New World and Old
World Otus are sister lineages or are more distantly related,
I couldn't say. So, the general thrust of this paper probably will turn out to
be correct. But I need a reason -- beyond my initial preconceptions, of course
-- to believe that these authors are correct, and they don't give me much of
one.
"George Barrowclough has a data set, doesn't he, on
owls? Strictly New World, or worldwide? If George ever publishes that. then my
bet would be that he would have data worth trusting. But unless someone can
convince me that the data used by Wink and Heidrich are a lot more robust than
I think they are, I'm not willing to endorse this study.
Comments from Robbins: "After reading Tom
Schulenberg's comments on the Megascops (# 58) proposal I change my
vote to "NO". Admittedly, I did not consult Wink and Heidrich (1999;
Tom is correct in pointing out that it is the correct citation) before voting
on this proposal. After reading this publication I totally agree with Tom on
all points. First, Tom is correct in stating that this work was not peer
reviewed (see Acknowledgements section in the above work). The fact that it was
dumped into a book amounts to it being no more than a "published by the
author" paper.
"Tom's comments concerning neighbor joining analysis
are on the mark and this work would not have been accepted had it been based on
those superficial analyses. His concerns that the authors didn't address
saturation issues, given the large percent sequence differences, in cytochrome
b are also well taken. Ignoring the non-informative neighbor joining tree,
let’s say that we put some faith in Wink and Heidrich's Maximum Likelihood tree
(Fig. 55a). You will note that Otus flammeolus is sister to
all (ones included in the study) New World screech-owls and all are not close
to Old World screech-owls. Thus, based solely on that tree, one would either
have to place flammeolus in whatever genus you put the other
New World screech-owls, or you would have to erect a new genus for flammeolus.
I suspect that no one would suggest the latter at this point. Thus,
leaving flammeolus in Otus while placing the other
New World screech-owls in Megascops is a very poor, partial
solution and, in fact, doesn't even represent what is presented by the
molecular data in Wink and Heidrich! Yes, it appears that Old World vs. New
World screech-owls are not monophyletic, but until we have a better data set that
can define limits I'm for maintaining all in Otus, or at a minimum,
we include flammeolus with the other New World screech-owls in
Megascops.
Comments from Remsen: "Tom and Mark are correct in
disputing the use of Wink et al. genetic data and analyses. The AOU CLC was
well aware of this problem and has not use any of those data as the sole basis
of making decisions. In fact, König and Wink themselves actually retained Otus for
New World birds in their classification. However, neither Tom or Mark mention
that the subgenus Megascops was recognized by Marshall on the basis of
vocal characters, and those vocal characters were amplified by König et al. On
the basis of vocal characters, migratory New World flammeolus fits
into the Old World group. The Wink-Heidrich genetic data, weak as they are, are
not only consistent with this but suggest a more important problem, namely that
broad Otus is polyphyletic. Whether cyt b is the
appropriate gene for investigating deep branches, and whether their genetic
distances are inflated, is indeed a concern, but in concert with the vocal
differences that owl experts consider important, the burden-of-proof in my
opinion is on those who would consider Otus to be a monophyletic taxon.
As it stands, Otus officially
(Ridgway) is diagnosed as "small owls, usually with ear tufts, and with
tarsi with not more than lower halves naked.' Use of body size, presence of ear
tufts, and degree of tarsal feathering to define a genus does not inspire much
confidence when mostly sedentary component taxa are scattered around the
planet. I'll go with recognizing two genera on basis of two independent data
sets rather than risk maintaining polyphyletic taxon."
Additional comments from Carla Cicero, 9/9/03: "here are my $0.02
worth: I agree with Tom's and Mark's concerns about the molecular analyses
conducted by Wink and Heidrich, including the problems with neighbor-joining
analysis and the lack of analysis of nucleotide saturation (they may have done
this, but it's not explicit in their methods section, which states that
"Details on methodology...can be obtained from the authors on
request."). On the other hand, I do think cytochrome b can be an
appropriate marker for examining divergence at this level if proper models are
considered. The addition of other markers (both mtDNA and nuclear) clearly
would strengthen the molecular analysis, but I reiterate Van's comments that
the basis for this proposal (and the AOU CLC decision) was the congruence of
the (admittedly weak) molecular data with the vocal differences. The fact that
Wink and Heidrich's different molecular analyses (including maximum likelihood)
all support polyphyly of broad Otus, which is consistent with
recognition of these genera based on fundamental differences in voice,
justifies this split in my mind.
"The question of what to do with O. flammeolus is
a separate and more complicated issue. Although the molecular data suggest a
basal sister taxon relationship with NW Otus, this relationship is
poorly supported (< 50% bootstrap) and placing flammeolus in Megascops conflicts
with the vocal data. The most conservative approach is to maintain this taxon
in Otus until additional molecular data resolves its
relationship."
Comments from Jaramillo: "YES While I understand
concerns over the adequacy of the genetic work, the fact that this division was
first proposed based on vocal characters, migratory tendencies and fits a clear
biogeographic pattern (Old versus New World) convinces me that making this
split is warranted. I also vote to keep flammeolus in Otus until
its correct placement can be determined. The genetic data does convince me that
Otus as it is now is polyphyletic, and needs to be rearranged."
Comments from Silva: "YES. The vocalization and
distribution data may be regarded as a good indicator that there are two
distinct genera within Otus."
Comments from Stotz: "YES. The molecular data in
this case is not strong, and if we had to use it to determine much beyond the
fact that Old World and New World taxa are distinct units, I would be
disinclined to pay much attention to the results. However, these results match
up with biogeographic and vocal data. As noted by Van, Megascops had
been recognized purely based on vocal grounds by Marshall. This is a case where
we are not relying entirely on molecular data to make this decision."
Comments from Nores: "NO. Yo
"no estoy de acuerdo" de elevar el subgénero Megascops a
género, sobre todo después de leer los comentarios de Schulenberg. De todos
modos, las razones dadas por Cicero y otros comentarios parecen también
válidos, especialmente en lo que se refiere a las voces."