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Proposal (736) to South American Classification Committee

 

Elevate Cyanoloxia cyanoides rothschildii to species rank

 

Background

Edward Bartlett first described Guiraca rothschildii in 1890, based on a set of specimens from Guyana. He compared those specimens to others of G. cyanoides (= Cyanocompsa cyanoides) and G. cyanea (= Cyanocompsa brissonii); he considered the birds from Guyana different enough to treat them a separate species. The author stated that “this well-marked species by its size, colour, and straight culmen cannot be confused with either Guiraca cyanea or Guiraca cyanoides, the two nearest allied forms, although it possesses characters of both, being an intermediate phase which might readily be taken for a hybrid.” (Bartlett 1890).

 

Guiraca rothschildii was later considered as a subspecies of G. cyanea by Berlepsch and Hartert (1902), but Hellmayr (1905) argued that not only was a “decidedly distinct form from G. cyanea”, but also that it was a southern representative of G. concreta cyanoides (= Cyanocompsa cyanoides cyanoides).  In his revision of the genus Cyanocompsa, Todd (1923) included G. rothschildii as a subspecies of C. cyanoides (as Cyanocompsa cyanoides rothschildii), but also stressing that it is a very distinct form with a much brighter coloration than other C. cyanoides and that is “possibly entitled to specific rank”

 

New information

Bryson et al. (2014) analyzed a multilocus dataset (ND2, ACO1, FGB5, and MYC) considering all species in the ‘Blue Clade’ of the Cardinalidae family (Klicka et al 2007). Their results showed that the lineage of C. cyanoides occurring east of the Andes (and corresponding to C. c. rothschildii) has been evolving independently from those west of the Andes for at least 3 Myr. Later, García et al. (2016) analyzed variation in two other mitochondrial markers (COI and cyt b) as well as phenotypic variation within the species. Cyanocompsa c. rothschildii was shown to be the most differentiated subspecies in song, plumage coloration, body, and bill size, and the results obtained for the molecular markers were consistent with those of Bryson et al. (2014).

 

Analysis and Recommendation

 I consider that the evidence showing differentiation in molecular markers, phenotype and song is strong enough to elevate rothschildii to the species level. This proposal would eliminate the subspecies C. c. rothschildii and add the species Cyanocompsa (now Cyanoloxia) rothschildii to the South American list.

 

References

BARTLETT, E. 1890. On a new species of Guiraca. The Annals and Magazine of Natural History 6, 168-169.

von BERLEPSCH, H. & HARTERT, E. 1902. On the Birds of the Orinoco region. Novitates Zoologicae 9, 1-135.

BRYSON, R. W., J. CHAVES, B. T. SMITH, M. J. MILLER, K. WINKER, J. L. PÉREZ-EMÁN, J. & KLICKA, J. 2014. Diversification across the New World within the ‘blue ’cardinalids (Aves: Cardinalidae). Journal of Biogeography 41, 587-599.

GARCIA, N. C., BARREIRA, A. S., LAVINIA, P. D. & TUBARO, P. L. 2016. Congruence of phenotypic and genetic variation at the subspecific level in a Neotropical passerine. Ibis 158, 844-856.

HELLMAYR, C. E. 1905. Notes on a collection of Birds made by Mons. A. Robert in the district of Pará, Brazil. Novitates Zoologicae 12, 269-305

TODD, W. E. C. 1923. A review of the genus Cyanocompsa.  Auk 40: 58-69.

 

Natalia García, January 2017

 

 

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Comments from Stiles: “A very tentative YES.  The coincidence of morphology, genetics and vocalizations is good, but I personally believe that at least among the oscines, what would really clinch this are playback experiments, given the variation in songs between populations of undoubted species; the study by Cadena et al. on Henicorhina anachoreta is a good example.”

 

Comments from Areta: “YES, although this might be to some extent a matter of taste. The, for a blue-grosbeak, relatively well-defined and congruent differences in morphology and vocalizations seem to me consistent with species status of rothschildii. I would have liked some spectrograms to see how these birds differ in songs, and some pictures to see how much they differ in plumage/morphology. Given that differences are not tremendously marked and genetic divergences are not very deep, playback experiments would have added unquestionable evidence on the species limits (I agree with Gary in this). However, due to the wide geographic range of C. cyanoides, it seems difficult to achieve.”

 

Comment from Josh Beck: Although this obviously just one data point, when I first heard rothschildii in the Amazon (Vaupes, Colombia) it took me a bit to realize what I was hearing. Impressed by the vocal difference, I tried playback of song from Panama and received no response. After, using a recording of rothschildii, I did receive a strong response. N=1 but in case anyone is interested in the anecdote... “

 

Comments from Pacheco: “A tentative YES. I do not know the populations that occur west of the Andes. Anyway, at this moment, the evidence in favor of a species status to Amazonian rothschildii seems to me sufficient.”

 

Comments from Cadena: “NO. This is a hard one. True, rotschildii differs in external phenotype and song from other populations in the complex, has been evolving in isolation for considerable time as evidenced by molecular markers, and is isolated biogeographically by the Andes. Are the differences marked enough so that one might infer this taxon is reproductively isolated from the rest? We don’t know for sure, and some may argue it doesn’t matter given their physical/geographic isolation and status as a distinct lineages. But, for better or worse, we follow the Biological Species Concept (do we? I really think this is something we need to discuss!), and I do not think we have sufficient evidence for the split under this concept.The anecdote by Josh Beck about lack of response in a playback trial is indeed suggestive because lack of response surely says a lot more than response in cases like this, but a formal analysis with appropriate sample sizes is lacking. I should note here that in the past I have been forced to make admittedly unsatisfactory recommendations to split taxa with similar evidence, e.g. in the Arremon torquatus complex. A crucial difference with cases like that is that in “A. torquatus” we found evidence for distinct species in regional sympatry, which required making taxonomic changes involving allopatric populations simply making the best of a bad situation. Another case in point was that of Anthocephala – here there was no need to make a change because no evidence of reproductive isolation in sympatry was available, but comparisons with the degree of differentiation among good species of hummingbirds pointed in the direction of the split. Given that the evidence here is not entirely convincing under BSC-criteria (I guess this is why others said their votes were tentative) and that we are not forced to make any changes, I vote no. If we were following the Phylogenetic Species Concept or lineage-based concepts, the split would be clearly justified.”

 

Comments from Robbins: “YES, to recognizing Cyanoloxia cyanoides rothschildii as a species.  Based on the genetic data coupled with plumage morphology and vocal data.  There are several online audio recordings at xeno-canto and Macaulay from both sides of the Andes that demonstrate how different song is."

 

Comments from Zimmer: “YES.  As others have noted, the congruence of published molecular data sets with plumage, structural and vocal differences, particularly within a group for which plumage appears evolutionarily conservative, is enough to override my concerns that the vocal differences, as presented here, are primarily anecdotal.  My personal experience has been that Blue-black Grosbeaks seem to sound at least slightly different at each different region that I visit within Amazonia, but they are all consistently different from Central American populations west of the Andes (whereas those populations don’t seem to vary nearly so much).  Some quantitative vocal analysis, especially combined with playback trials, could really cement my thinking on this, but even in the absence of such data, I’m still ready to take the plunge.”

 

Comments from Jaramillo: “YES. I understand the reticence from some members given that playback was not done, or another test of reproductive isolation. However, the suggestion here from the molecular data is that this a very separate lineage. Sampling seems solid in the paper, and this added to known morphological differences, as well as the understanding that plumage coloration is conserved in this group, I do not have a problem accepting rothschildii as a species. Would the name be Rothschild’s Grosbeak? Or is there another option?”

 

Comments from Claramunt: “YES. I have checked some skins here at the ROM and I agree with all previous authors, including García et al.: rothschildii is well-differentiated from cyanoides (and brissonii = cyanea) based on plumage. C. rothschildii has a pure bluish hue instead of the greenish-blue of the former. In that respect, it is more similar to C. brissonii. My impression is that there are three main forms, cyanoides, rothschildii, and brissonii, which rothschildii being closer to cyanoides in morphology but closer to brissonii in color. Lumping rothschildii with cyanoides, was an arbitrary decision; Todd admitted that rothschildii is “…a very distinct form, … and is possibly entitled to specific rank.” Nobody afterwards showed any evidence of introgression or reproductive compatibility between rothschildii and cyanoides.

 

“The evidence for the existence of three main lineages (cyanoides, rothschildii, and brissonii) comes from the good match between mitochondrial and plumage variation, suggesting a history of independent evolution with no intergradation (i.e. a history of reproductive isolation). Note that the cyanoides-rothschildii divergence is not a cis- versus trans-Andean split, because cyanoides occupies foothills of the eastern cordilleras in NE Colombia and Venezuela facing the Orinoco basin (both plumage and mtDNA agree on this).

 

“Potentially, there could be a contact zone between cyanoides and rothschildii along the foothills of the SE Colombian Andes but so far there is no information from that area and the lack of information may represent a true gap in the distribution of these forms. Sampling in García et al. is sparse and did not include data from near the putative contact zone (no birds from Venezuela or E Colombia). Most of the statistical tests used the traditional subspecific taxonomy as grouping criteria and evaluate differences in the means. Such an approach cannot be used to test the traditional groupings and cannot distinguish clinal variation from discontinuities in the face of geographic variation. With those caveats, the marked color differences of rothschildii are evident in the color PCA (no overlap in color PC1, Fig. 2a), whereas the other subspecies of cyanoides show overlap and seem part of a cline. The only “partial” coincidence between phenotype and genotype mentioned by García et al. refers to variation among trans-Andean subspecies, I guess, because I don’t see any sign of mismatch for rothschildii vs. cyanoides.

 

“Finally, evidence for a sister relationship between rothschildii and cyanoides is very tenuous (no statistical support, and they are not even sister taxa in some analyses: Bryson et al. Fig. 2). Therefore, I think this proposal should be viewed as a correction of a historical error: lumping rothschildii into cyanoides. Regardless of the lack of information on intrinsic reproductive isolation, I think that mitochondrial and phenotypic variation clearly points to the presence of two isolated and differentiated species.”

 

Comments from Remsen: "YES, somewhat reluctantly.  Although I side strongly with Daniel on every point he makes, I am persuaded by Santiago's arguments that we are correcting a weakly supported historical decision and that there are no strong arguments FOR considering them conspecific. My assessment is that burden of proof falls on treating them as conspecific.  Too bad Santiago or someone of his caliber was not a reviewer on the paper.

 

“Here are photos of specimens, with from top to bottom: brissonii, cyanoides, and rothschildii. These illustrate some of the plumage differences noted in the proposal, especially how distinctive rothschildii with respect to the other two.

 

 

 

“Now, we need a proposal on English names.  Hellmayr (1936) used "Blue-black Grosbeak" for concreta (n. Middle America), "Costa Rican Blue Grosbeak" (s. Central America), "Panama Blue Grosbeak" (Panama, NW South America), and "Rothschild's Blue Grosbeak" (Amazonia etc.).  Thus, not much help there."