Proposal (229) to South American Classification Committee
Split Coccycua
from Coccyzus
Background: The traditional classification of New World Cuculinae
consists of four genera, in the following sequence:
Coccyzus
Saurothera [extralimital]
Hyetornis [extralimital]
Piaya
I'm not sure if any explicit rationale has ever been published to
justify this traditional linear sequence. The species membership in both genera
reflects plumage similarities, and has remained fairly stable for a century or
so. Ridgway's (1916) classification of North American species is essentially
the same as that of AOU (1998) and SACC in terms of generic limits, with the
exception that he retained our Piaya minuta in the monotypic genus Coccycua.
See Sorenson & Payne (2005) [let me know if you need pdf] for a synopsis of
work on the group this century, none of which had sufficient taxon-sampling or
resolution to force a change in classification.
New information: Sorenson & Payne (2005)
analyzed mitochondrial (ND2) DNA and ribosomal RNA (12S) sequences (1000+ bp
each) to produce a phylogeny for the family as a whole, with outstanding
taxon-sampling. A summary of the relevant findings for our Coccyzinae (from
Fig. 5.5) is as follows:
1. The species of the two genera above, plus Caribbean Hyetornis
and Saurothera, comprise a fairly strongly supported group (87%
bootstrap).
2. Piaya is not monophyletic if minuta is included;
the latter forms a monophyletic group (96% bootstrap) with two South American
species ("Coccyzus" pumilus and "C." cinereus).
Sorenson & Payne resurrect Coccycua for this group. Coccycua is
basal in the group.
3. Extralimital Saurothera and Hyetornis are
embedded within the remaining Coccyzus; they form a monophyletic group
(95%) but are more closely related to C. erythropthalmus and South
American C. lansbergi than the latter are to other Coccyzus,
e.g., C. americana. Therefore, to maintain a monophyletic Coccyzus
(100% bootstrap; with pumilus and cinereus removed), they
merged both genera into Coccyzus.
Sorenson & Payne's (2005) tree (Fig. 5.5) would produce the
following linear classification (by convention, with basal taxa first, and with
taxa arranged roughly from north to south and west to east within sister taxa).
I did this independently from Sorenson & Payne's linear sequence in their
table of contents and came up with exactly the same sequence:
Coccycua minuta
Coccycua pumila
Coccycua cinerea
Piaya cayana
Piaya melanogaster
Coccyzus melacoryphus
Coccyzus americanus
Coccyzus euleri
Coccyzus minor
Coccyzus erythropthalmus
Coccyzus lansbergi
Analysis: As noted by Sorenson & Payne, their new groupings also make
some "sense" to a degree in terms of plumage and natural history. The
species in Coccycua share similarities in bill shape and small body
size. Ridgway (1916) placed pumilus and cinereus in their own
genus, Micrococcyx, based on wing shape. Hyetornis and Saurothera
have vocalizations and plumage similar to true Coccyzus, and their large
body size and more rounded wings reflect patterns in morphological evolution of
insular birds in general. The only surprise to me was expulsion of minuta from
Piaya, but after fiddling around with the skins in our synoptic series,
it seems fairly clear that chestnut plumage "comes and goes"
throughout this group of cuckoos as a whole, which seem to have repeated
plumage themes that reappear among unrelated species and groups.
Recommendation: Sorenson & Payne's data set and analysis
are clearly superior to any previous "data" and should be reflected
in our classification and linear sequence, and I strongly recommend a YES vote
to change our sequence to the one above.
Literature cited:
Sorenson, M.D. & R.B. Payne. 2005. Molecular systematics:
cuckoo phylogeny inferred from mitochondrial DNA sequences. Pp. 68-94 in R.B.
Payne. Bird Families of the World: Cuckoos. Oxford University Press.
Van Remsen,
Aug. 2006 (in consultation with Bob Payne)
Note: This proposal is a slight modification of the one to AOU/NACC.
It was accepted by NACC - see Banks et al. (2006).
________________________________________________________________________________________________
Comments from Stiles: "YES. The analyses look
solid. Differences in wing shape between minuta and the other two
species could simply reflect sedentariness in the former, migratory behavior in
the latter."
Comments from Robbins: "YES. Sorenson & Payne
(2005) provide solid genetic data for resurrecting Coccycua for minuta
and its two close relatives."
Comments from Zimmer: "YES. Evidence seems strong.
Despite plumage similarities of minuta to Piaya, it is clearly
more divergent vocally from cayana and melanogaster than either
of those species is from one another."
Comments from Jaramillo: "Yes and NO - Yes,
split Coccycua from Coccyzus, but No on the actual
membership of Coccycua. The issue is more than just wing shape, or
chestnut in the plumage, but I need more convincing that minuta is not a
Piaya. The bill morphology of minuta to me is much more like
Piaya, than Coccycua. Small size may link these three species,
but minuta is small for a Piaya, as a Coccyzus it actually
would be rather a large one. So really small size links pumila and cinerea,
but not minuta. The green bill of minuta is unlike all other
cuckoos in this group except Piaya cayana. The highly graduated tail of minuta is
like Piaya or Coccyzus, while pumila and cinerea have
much less strongly graduated tails. Vocally, pumila and cinerea outwardly
sound quite different, but the repetitive nature of the songs and the tempo is
similar. The explosive nature of some Piaya calls (the chip-churr call
of cayana for example) seems to be matched by a call of minuta
on the Hardy tapes (assuming correct identification). There is also a purring
call attributed to minuta on Xeno-canto that sounds similar to that
of Piaya melanogaster. The common 'chwip" call to me sounds
allied to calls of Piaya cayana rather than Coccycua (I
know cinerea pretty well from Argentina, but pumila only from
recordings). This is more from the gut than anything else, but I do want to
raise the question of whether the analysis could have mis-represented the
relationship of minuta? Maybe others more familiar with the methodology
could comment. I just think that pumila and cinerea "make
sense" to me, but not minuta, not at all." [Note from Remsen -- I'll record this as a NO vote.]
Comments from Pacheco: [NO] "Yes" to accept pumilus
and cinereus apart from Coccyzus, but "no"
considering strictly the title of this present proposal. The type-species of
genus Coccycua is Cuculus monachus = Coccyzus minutus [Little
Cuckoo]. More recently, conclusions of Hughes (2006. Systematics and
Biodiversity 4: 483-488) support the resurrection of Micrococcyx to
incorporate the Ash-coloured and Dwarf cuckoos, and the monotypic Coccycua
for the little cuckoo."
Comments from Bob Payne: "Here are comparisons of the trees in Hughes (2006) and Payne
(2005). Our tree is a complete species taxa sample of cuckoos, it is not
limited by choice of a single (questionably appropriate) outgroup taxon to root
the tree, and it has much higher bootstrap values, especially for the
clade/non-clade in question, Coccycua. I ran the Hughes 2006 paper past
Mike Sorenson, and he agrees the outgroup problem is the major problem with
that paper."
"Hughes (2006) presented a tree of
molecular phylogeny of certain cuckoos. The tree did not recover a clade that
included Coccycua with minuta and cinerea, distinct from
the other New World cuculine cuckoos. Otherwise, the tree is consistent with
the estimate of cuckoo phylogeny in Sorenson & Payne (in Payne 2005). The
following compares the taxon sampling and bootstrap support for the clade in
question, and indicates stronger support for the tree in Sorenson & Payne
(2005).
"Taxa: 18 species are recognized in New
World Cuculinae (Payne 2005). All 18 species were sequenced in Sorenson &
Payne (2005). Basal to the other species was a clade composed of minuta,
pumila, and cinerea; the clade had 96% bootstrap value, and the
genus Coccycua Vieillot 1816 was recognized for the clade. Within
this clade, minuta was basal, and the sister clade with pumila and
cinerea had 100% bootstrap support, this sister clade corresponds to
"Micrococcyx" Ridgway 1912. The taxa most closely related to
these New World cuckoos in the mitochondrial phylogeny were the Old World
malkohas (Phaenicophaeus and 5 other genera) and crested cuckoos (Clamator).
"Hughes 2006 included only 11 of the 18
species taxa of New World cuckoos, with a single outgroup taxon, Cuculus,
to root the phylogeny. Hughes 2006 tree showed 10 of these New World cuckoos
(including minuta, excluding only cinerea) to be a clade.
This clade (excluding cinerea) had a bootstrap support of only 69%. The
consensus tree did not show cinerea and the 10 New World cuckoos to
be more closely related to each other than cinerea was to Cuculus
- the 10 species, C. cinerea, and Cuculus formed an
unresolved three-branch polytomy.
"Hughes 2006 tree with 11 taxa was
otherwise consistent with Sorenson & Payne 2005 tree for the 18 New World
taxa. Both indicated the "Coccyzus" of Peters 1940 was
polyphyletic.
"Numerical comparison of the trees: the
bootstrap support value for a 3-species Coccycua clade was 96% in
Sorenson & Payne 2005. The bootstrap support for a clade that included Coccycua
minuta and excluded cinerea was much lower, 69% (Hughes 2006), and
the latter tree did not sample the species pumila.
"Hughes 2006 tree had fewer taxa, it did
not include the closest relatives of the New World Coccyzus group: the
malkohas and the crested cuckoos. The choice of a single, distantly related
cuckoo (Cuculus) probably affected the rooting of Hughes 2006 tree;
another outgroup might have recovered the three-species Coccycua clade.
The lower bootstrap results indicate lower support for the Hughes 2006 tree
than for Sorenson & Payne 2005 tree.
"Hughes (2006) proposed recognition of
another genus, Micrococcyx Ridgway 1912, based on the lack of recovered
clade that includes minuta and cinerea. Hughes did not compare
the other pumila, which is generally thought to be closely related to cinerea.
"Hughes & Baker 1999
("Phylogenetic relationships of the enigmatic hoatzin (Opisthocomus)"
Molecular Biology & Evolution, 1999, 16:1300-1307) reported a genetic
phylogeny of several cuckoo taxa, including "Chalcites," Cacomantis,
Crotophaga, Guira, and Neomorphus, using the same mitochondrial
genes as Hughes 2000. Why were these not included in Hughes 2006, as outgroups?
And, Hughes 2003, Naturwissenschaften 90:231-233 reported molecular
phylogenies in other New World cuckoos, using the same genes, but these were
not compared in Hughes 2006 to the Coccyzus group. The choice of
outgroup taxa (a single taxon) is of greatest concern in interpreting Hughes
2006.
"Also, Hughes & Baker (1999) was based
on certain erroneous nucleotide sequences (as evaluated in Sorenson et al.,
2003, "More taxa, more characters: the hoatzin problem is still
unresolved." Mol. Biol. Evol. 20:1484-1499; not cited in Hughes
2006, where Hughes & Baker 1999 was cited).
"Elsewhere, Hughes 2000 had a tree based on
morphological characters that showed Coccyzus most closely related
to Clamator (as in Sorenson & Payne 2005). Coccyzus was
less closely related by numbers of branches to Cuculus (or to Tapera,
as in an earlier ms version of Hughes 2006). Hughes 2000 (a morphological
comparison) listed Clamator as sister genus to Coccyzus, but
Hughes 2006 did not compare genes of Clamator.
"The morphological characterization for the
three-species Coccycua genus in Payne (2005) was: "Small New World
cuckoos with a rounded to graduated tail. The type, by monotypy, is Coccyzus
minutus Vieillot (Peters 1940), which has rufous plumage and short rounded
wings. Wing shape is rounded in Coccycua minuta, intermediate in C.
pumila and pointed in C. cinerea, although not as pointed as in most
Coccyzus cuckoos." Partly
this follows the descriptions and comparisons in Ridgway (1912). Hughes 2000
did not report on the morphology of pumila or cinerea.
"In summary, the phylogenetic estimate and
the systematic treatment of cuckoos in Payne (2005) have better support than
the estimate and systematics in Hughes (2006). Both agree that the broad-sense
genus Coccyzus of Peters is polyphyletic, and both agree that the large
lizard-cuckoos "Saurothera" of the West Indies are within the
monophyletic narrow-sense genus Coccyzus."
Comments from Schulenberg: "YES, although I don't think
our work is done. I agree with Fernando that what we probably are looking at is
a monotypic Coccycua (minuta), and another genus for pumilo
+ cinerea. I haven't seen Hughes 2006, and if Payne and Sorenson are
right, then maybe I needn't bother. But I don't see that the Sorenson and Payne
phylogeny is inconsistent with a two-genus "solution" for these three
species either."