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 it 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."