Proposal (180) to South American Classification Committee
Lump Sternoclyta
and Hylonympha into Eugenes (Trochilidae)
This proposal would lump two
monotypic genera of our baseline list and nearly all of the literature into a
third monotypic genus, Eugenes of
Central America, as proposed by Renner & Schuchmann (2004) (hereafter
R&S).
The single species of Sternoclyta and
Hylonympha are confined or nearly so to Venezuela (S. cyanopectus
has recently been taken in adjacent Colombia). Both occur in mountainous
regions, H. macrocerca in the coastal mountains of NE Venezuela, S.
cyanopectus in the coastal ranges further W and on the slopes of the Mérida
Andes. The status of the two as monotypic genera has been essentially
unquestioned until recently; Schuchmann (1999) considered them both close to Heliodoxa,
which he in turn considered close to the Middle American genus Eugenes.
This genus is also monotypic, its one species (as currently recognized) ranging
from extreme SW USA to W Panama. The southernmost form, spectabilis (sometimes
considered a separate species) occurs at high elevations (mostly above 2500 m)
in Costa Rica and Panama.
In most previous classifications
(e. g., Cory 1918, Peters 1945), all three of these genera have been placed
near to each other and near or adjacent to at least some of the forms currently
included in Heliodoxa. Johnsgard (1983) actually lumped Eugenes into
Heliodoxa. However, recent genetic data (Bleiweiss et al.1997, Altshuler
et al. 2005) have shown that these two genera are in fact not closely related
but belong in different clades of the Trochilinae.
The close association of Eugenes
and Heliodoxa in previous classifications seems due to the fact
that in both, the feathering of the forehead and chin extends unusually far
forward over the base of the bill. However, Wetmore (1965) noted that in Eugenes
the operculum is bare whereas in Heliodoxa it is feathered, and
considered that the resemblance was superficial and not sufficient reason for
lumping them. The authority cited for recommending their lumping is Zimmer
(1951), but a careful reading of his paper makes it clear that this interpretation
is based on nothing more than a lapsus calamus.
Zimmer actually did lump several monotypic genera into Heliodoxa,
including Phaiolaima, Ionolaima, Agapeta, Lampraster
and Eugenia. On p. 3 of this paper,
he mentions Eugenes but not Eugenia and states that in all
of these (other genera) the tail is forked, reaching its "maximum depth of
furcation in "Eugenes" where the rectrices are narrower than
in the rest". That he was actually referring to Eugenia imperatrix
and not Eugenes fulgens is made clear by the fact that the
tail of the latter is not more deeply forked than those of several species of Heliodoxa
and the rectrices are not narrower, whereas in the former both statements are
true; and on p. 15 of the same paper in his treatment of H. imperatrix,
he refers to its former genus as "Eugenia" while noting that
on p.3 he gave reasons for lumping it with Heliodoxa and repeating its
characters of more elongate tail and narrower rectrices (but on p. 3, Eugenia
is never mentioned, only Eugenes!) This makes it clear that Zimmer never
advocated lumping Eugenes into Heliodoxa - he never intended
to mention it at all!
Schuchmann (1999) continued to cite
a relationship between Eugenes and Heliodoxa, while intimating
that Sternoclyta and Hylonympha were closely related to the
former, evidently paving the way for R & S´s lumping. In addition to citing
Zimmer's supposed lumping of Eugenes (an indication of things to come),
they also cited Bleiweiss (1998) as advocating a "link" between Eugenes and
the genera Acestrura and Lophornis “based on DNA hybridization
studies". This statement is simply incredible since Bleiweiss's dendrogram
clearly places these three genera in three different major clades. The "bee" clade containing Acestrura
is actually most closely related to the "mountain-gem" clade
containing Eugenes, although by no stretch of the imagination can these
two genera be so considered; the "coquette" clade of Lophornis
is more distantly related to these two, as is the "brilliant" clade
that includes Heliodoxa. The study of Bleiweiss et al. (1997; the 1998
paper only presents briefly the cladogram) is the most thorough and complete
DNA-DNA hybridization work yet reported. Moreover, a very detailed study
involving sequencing of three genes (mitochondrial and nuclear) and many more
taxa (Altshuler et al. 2004) strongly supported nearly all of Bleiweiss's
conclusions, including the major clades. Hence, the genetic evidence against a
close relationship of Eugenes to Heliodoxa is overwhelming.
Thus, it is interesting that R & S discount such evidence because it
"may be misleading in the absence of morphological, ecological and
biogeographical data". I now turn to their attempt to supply such data.
Their study is based upon a rather
detailed comparison of plumage colors and patterns of E. f. fulgens, E.
f. spectabilis, S. cyanopectus and H. macrocerca, particularly of
the males; characters include the combination of purple crown and green gorget
or throat and black belly (though this latter is hardly true of S. cyanopectus),
the precise colors and patterns of the green disks below, the presence of a
pale malar stripe in the females, etc. They devised 10 such characters for a
cladistic (PAUP) analysis that included Heliodoxa schreibersii (the most
similar species of this genus in male color and pattern) and use as an outgroup
Coeligena iris, one of the most different-looking members of that genus
(and with a distribution far from the three genera of interest). The resulting
cladogram shows Eugenes and Hylonympha to be sister genera (and
species), with Sternoclyta sister to these, H. schreibersii next
and finally the outgroup Coeligena most distant. There are several
problems here. First, the characters used in the analysis are notoriously
subject to sexual selection and homoplasy: one can easily find green gorgets,
malar stripes and black bellies and various other features in species of
unrelated genera. Second, when plumage features of this type are used the
choice of similar or different-looking species from large genera like Heliodoxa
or Coeligena can easily load the dice so that the cladogram supports
one's preconceived notions (see below). Third, if the genetic evidence is
anywhere near correct the starting point of the analysis is wrong: Heliodoxa
and Coeligena are members of the same clade, far more closely
related than either is to Eugenes - hence using one as an outgroup and
the other as an ingroup will inevitably produce spurious results.
R&S mention a fairly impressive
number of specimens examined, but few statistical analyses of measurements were
done. Over _ of the specimens measured were of E. f. fulgens; sample
sizes of the other forms range from small to pitiful. For H. macrocerca,
data for only 1-3 males and an undisclosed number of (presumably 1 or 2)
females were presented. Amazingly, 72 additional specimens were
"unmeasured" because they "were damaged or lacked geographical
information". Given that the objective of the study was not to look for
geographic variation in this species, which in any case has a total range only
ca. 100 km long; it is rather difficult to fathom this reluctance. Less extreme
but similar cases occurred with most other forms, such that careful
morphological analyses were for the most part avoided (and Wetmore's opinion
was not cited). Similarly, about the only "ecological evidence"
presented was to the effect that all occur in mountains, albeit with different
elevational ranges - nothing on details of habitat, food plants, behavior etc.
The "biogeographical
evidence" presented is a "speciation model" that begins with an
Amazonian "proto-Heliodoxa" ancestor much like H. schreibersii and postulates
progressive movements of populations into the Andes and on to the coast ranges
of Venezuela and the mountains of Central America, presumably tied to
Pleistocene glacial-interglacial cycles. This model makes interesting reading
but the solid supporting evidence is essentially zero; its validity relies
heavily on the taxonomy proposed and if the taxonomy is suspect, the model
collapses. (One suspects that the taxonomy was tailored to fit the model, in
which case taking the speciation model as support for the taxonomic conclusions
would be circular reasoning at best).
Finally, I return to the initial
question: is the evidence for lumping Sternoclyta and Hylonympha into
Eugenes convincing? I find the arguments severely flawed, particularly
if one accepts the strong genetic evidence against a close relationship of Eugenes
to Heliodoxa. (The labored arguments of R & S to discount
Bleiweiss´s supposed linking of Eugenes with Acestrura and Lophornis
and thus genetic evidence generally, can be ignored: they themselves were the
only ones to propose this straw man). Clearly, given the very distant
relationship of Eugenes to Heliodoxa, if Sternoclyta or Hylonympha
are closely related to one, they cannot be to the other and a cursory look
indicates that the former, perhaps both may be much closer to Heliodoxa.
The male plumage pattern of Sternoclyta is somewhat suggestive of that
of some Heliodoxa, e.g. schreibersii, the female plumage bears a
striking resemblance in pattern and color to that of H. leadbeateri and
its operculum is feathered. In all of these features it differs from Eugenes.
I do not have access to specimens of Hylonympha, but its main
resemblance to Eugenes appears to be in the colors of crown, breast and
gorget of the male; the female appears much more similar to those of some Heliodoxa,
notably H. leadbeateri: at best, I would consider its relationships
unresolved. (I note that the plate in HBW does make the male look like a
long-tailed Eugenes - but as I have the distinct impression that a
number of figures on these plates were drawn to order to fit Schuchmann's
taxonomy, I don't know how much reliance can be placed on this). Genetic evidence will probably settle these
questions, but must await sequencing of genes in Sternoclyta and Hylonympha.
Certainly, the lumping of these genera into Eugenes is untenable on
current evidence and I strongly recommend a NO vote on this proposal.
References
Altshuler,
D. L., R. Dudley & J. McGuire. 2004. Resolution of a paradox: hummingbird
flight at high altitudes does not come without a cost. Proc. Natnl. Acad. Sci.
USA 101:17731-17736.
Bleiweiss,
R., J. A. W. Kirsch & J. C. Matheus. 1997. DNA hybridization evidence for
the major lineages of hummingbirds (Aves: Trochilidae). Mol. Biol. Evol.
143:325-343.
Bleiweiss,
R. 1998. Slow rate of molecular evolution in high-elevation hummingbirds. PNAS
95:612-616.
Cory 1918
Peters 1945
Renner, S.
& K-L. Schuchmann 2004. Biogeography, geographical variation and taxonomy
of the hummingbird genera Eugenes Gould, 1854, Sternoclyta Gould,
1858, and Hylonympha Gould, 1873 (Aves: Trochilidae). Ornithol. Anz.
43:103-114.
Schuchmann
1999: HBW, vol. 5.
Wetmore, A.
1965. The birds of the Republic of Panamá, vol. 2. Smithsonian Misc. Coll.,
vol. 150.
Zimmer, J.
T. 1951. AMNH Novitates no. 1513.
Gary
Stiles, July 2005
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