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 Mˇrida 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 Ņbased 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.
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.
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 Panam‡, vol. 2. Smithsonian Misc. Coll., vol. 150.
Zimmer, J. T. 1951. AMNH Novitates no. 1513.
Gary Stiles, July 2005