Split Pyrrhura pacifica from Pyrrhura melanura
Gene flow plays a critical role in the evolution of species (Slatkin, 1987). Speciation does not absolutely depend on a total interruption of gene flow, but we can be sure that if some factor causes a complete break in gene flow between two populations, and sufficient time passes after that break, then the two populations will evolve into two different species. Helbig et al. (2002) pointed out that sufficient time must have elapsed to ensure that even if the two taxa come into contact at some time in the future, they would not be able to interbreed.
Geology can be relevant here, because if geological processes are involved in the interruption to gene flow, that may allow us to date that interruption. Such a case occurs with Pyrrhura melanura, the Maroon-tailed Parakeet. This species has a number of taxa on the eastern side of the Andes: melanura in the lowlands of eastern Colombia, those of southern Venezuela in Amazonas and Bolívar, eastern Ecuador, eastern Peru, and Amazonian northwest Brazil east to the Rio Negro It also has several subspecies occurring along the eastern base of the Andes: souancei of eastern Colombia from the Macarena Mountains south to Putumayo; Ecuador: eastern base of North Andes in Sucumbíos, Napo, Pastaza and Morona-Santiago; and berlepschi of eastern Ecuador: eastern base of southern Andes in Morona-Santiago on Cordillera de Cutucú, & west of Macas in lower Río Upano valley of Sangay National Park; and Peru: Huallaga Valley; finally we have chapmani in Colombia: upper Magdalena Valley from southern Tolima to the head of the valley in Huila. The altitudinal range of these taxa is mainly lowlands to 500 m, but for chapmani 1600-2800 m.
We also have pacifica on the western side of the Andes. This occurs in southwest Colombia on the Pacific slope of Nariño, and in Ecuador: Pacific slope in northwest: Esmeraldas south to west Cotopaxi: Caripero area. Its altitudinal range is mostly 500-1400 m, locally down to 250 m along Río Verde in east Esmeraldas; and as high as 1900 m at Caripero.
Between these two groups we have the Andes. Note that the only gaps in the main Andes are well south of the range of pacifica: the Peruvian flat-slab segment (3 °S-15 °S), the Pampean flat-slab segment (27 °S-33 °S) and the Patagonian Volcanic Gap (46 °S-49 °S). The first one separates the Northern from the Central Volcanic Zone, the second the Central from the Southern and the last separates the Southern from the Austral Volcanic Zone.
According to Garzione & Hoke (2008), the Andes formed rather abruptly - between 10 and 6 million years ago - much faster than previously assumed. Given their altitudinal range, this means that cannot have been gene flow between pacifica and the taxa on the other side of the Andes for at least 6 million years and probably longer.
There are also morphological differences between pacifica and the other taxa. According to Ridgely and Greenfield (2001: 276), pacifica resembles the nominate race, in that it has narrow breast scaling, but in the case of pacifica, the breast is heavily suffused with a pinkish wash. It also differs in its shorter tail and greyish (not white) periophthalamic ring. Ridgely & Tudor end their account by stating that pacifica may deserve full species status.
Photos of both pacifica and melanura follow:
Choco Parakeet Pyrrhura pacifica Río Canades Esmeraldas Thanks to Lou Hegedus.
Maroon-tailed Parakeet Pyrrhura melanura Napo Ecuador Thanks to Mike Danziger.
The calls of the two groups also differ. These may be heard by going to my website, http://www.worldbirdinfo.net
Please click on Birds Search, and enter Pyrrhura pacifica as the search term, making sure that the Scientific Name button is operative. When the results appear, click on Choco Parakeet. When that species account opens, click on Media, and then click on the mp3 record under Sounds. The repeat the process, but entering Pyrrhura melanura.
Garzione, C. N., Hoke, G. D., Labarkin, J. C., Withers, S., MacFadden, B. J., Ghosh, P., and Mulch, A., 2008, Rise of the Andes: Science, v. 320, p. 1304-1307.
Helbig AS, Knox AG, Parkin DT, Sangster G, Collinson M. 2002; Guidelines for assigning species rank. Ibis, 144: 518-525.
Ridgely, R.S. & Greenfield, P.J., 2011. The birds of Ecuador: status, distribution and taxonomy. Comstock Publishing Associates, Ithaca, NY.
Slatkin, M. 1987. Gene Flow and the Geographic Structure of Natural Populations. Science 236, 787-792.
John Penhallurick, May 2012
Comments from Cadena: “NO, for a lack of published quantitative analyses. And of course, that a study focused on the Colombian Andes indicated rapid uplift over a specific time period need not imply that all of the Andes uplifted at the same time. Even if the northern Andes effectively also uplifted quickly and at the time when Penhallurick indicates, this says little to nothing about gene flow, as we know well that many species have crossed the Andes following their uplift and in some lineages this has occurred repeatedly. If one follows this logic, then it would follow that dozens of species with cross-Andes distribution should be split in two.”
Comments from Andrés Cuervo: “John Penhallurick might be right in that pacifica should be elevated to species rank, but I ignore if there is novel or overlooked information in the literature that would justify that change at this point. Nonetheless, I’d like to comment on two assumptions that people usually make and that may lead to justify a split with no rigorous evaluation of data.
“First, that present-day distributions (geographical and elevational) of organisms, and the biomes they inhabit, have been in stasis since their origin. By extension, people assume that if barrier A emerged X Mya, then current populations on opposite sides have that age. That may be true for some but certainly not for all organisms separated by a barrier; the only way to assess alternative scenarios is by having appropriate species-specific biological information. The proposal reads: “…if geological processes are involved in the interruption to gene flow, that may allow us to date that interruption. Such a case occurs with Pyrrhura melanura, the Maroon-tailed Parakeet”; however, interruption of gene flow in these parakeets has not been evaluated (please correct me if I am wrong), so there is no subject for temporal calibration (not to mention what the proper calibration is, it may not be the rise of the Andes after all!). Moreover, the geological paper cited is about the rise of the Andean Altiplano.
“The second assumption often made is that morphological differences immediately confer species status. This is circular reasoning. If pacifica is considered a valid subspecies (as it has been the case for a long time), then it must be phenotypically different at least from other races of melanura; otherwise, it would not be valid. Therefore, highlighting the existence of morphological distinctions to support a split is not really bringing new information as to whether the differentiated populations should be considered species (under the working definition of species endorsed here).”
Comments from Thomas Donegan: “It can seemably sometimes be tempting to pick up on drafting or technical points on a proposal and lose sight of the issue being considered. Such approaches may discourage proposals and result in not fully considered decisions. The below comments are focused on considering the split set out in the proposal, which is an issue we looked at briefly when producing the recent Colombian field guide / checklist versions. There are probably lower fruit out there in terms of taxonomic changes, and we have not adopted this split to date because all the necessary data are probably not yet available to revise the group.
“Voice: Parrots are the best-studied example of a family in which voice can be learned, even from humans. Also, there are some sympatric species that are vocally almost identical (e.g. Brotogeris in Amazonia), so voice is not often used in considering species limits. An inspection of recordings on xeno-canto reveals similarity in note shape, overtone patterns, and frequency among these birds (follow link below and click on 'sonograms'):
“Plumage and Distributions: As set out in the proposal, pacifica is geographically isolated from other populations and separated by the Andes in one of its highest parts. It occurs only in southwestern Colombia and is not found in the Cauca or Magdalena valleys. Most of the rest of the group occurs east of the Andes. However, the proposal somewhat brushes over the most oddball pieces of this puzzle - subspecies chapmani which occurs in the southern Central Andes (so 'west of the Andes') but close to the Amazonian distribution of melanura and subspecies souancei of the Colombian east slope, each of which occur at higher elevations than melanura. The distribution and plumages of this group in Colombia are well-summarised in the Rodriguez & Hernandez book. Subspecies melanura has extensive mottling on the upper breast; pacifica has much reduced speckling, and in chapmani the speckling extends to a nuchal collar. The plate in Restall field guide somewhat exaggerates the darkness of the orbital ring of pacifica, as can be seen in photos from the following ProAves database photo on Flickr. The orbital is a light rather than dark grey:
“Any consideration of this group probably needs also to consider the correct placement of other subspecies, particularly chapmani but also some of the other eastern forms such as souancei that occur close to the distribution of the nominate subspecies. The various subspecies of melanura are among the most marked taxa in the genus that are currently treated as conspecific, and this is a difficult genus more generally, as shown from the SACC's picta proposals. If one were to apply the new 'species scoring' system of Tobias et al. or adopt comparative splitting considering differences between these alongside recently split members of the picta group, one could potentially come up with a reasonable basis to split various of them. Whether or not to adopt this approach at present should be a consideration based on plumages and distributions.
“My personal view is that a more detailed analysis including a consideration of voice, biometrics and molecular data of the whole group is needed to take this one forwards, in light of the lack of vocal differences and puzzling distributions. The proposal to split pacifica may well be correct as part of dealing with this group, but such a treatment may be an incomplete and overly simplified approach.”
Comments from Stiles: “NO, at least on currently available evidence. I think that the critical area for determining which and how many species should be split off from P. melanura is Colombia, particularly in view of the intervening form chapmani. Genetic and vocal evidence from this area are the critical data that would be needed. That melanura and pacifica differ genetically in Bolivia is interesting, but this represents the oldest part of the high Andes; the orogenic events that may have separated the three forms in Colombia are much more recent, and if gene flow still occurs here we might be seeing something like a “ring species” situation.”
Comments from Pacheco: “NO. Considerando as opiniões acima emitidas, enquanto não houver uma análise publicada da situação.”
Comments from Robbins: “NO. When Bob Ridgely and I described P. orcesi in 1988 we recognized that the P. melanura complex probably consisted of multiple species, including pacifica which is likely sister to orcesi; however, what is needed is a comprehensive molecular data set to address this question given how morphologically similar this group is and Pyrrhura as a whole.”
Comments from Zimmer: “NO. The biogeographical and morphological distinctions cited in the proposal are certainly suggestive, but I would echo the calls of others for an actual analysis of the entire melanura complex before splitting pacifica on what currently amounts to circumstantial evidence.”
Comments from Nores: “NO. This proposal has a lot of unnecessary and little necessary information. Even if Penhallurick might be right that pacifica should be elevated to species rank, as indicated by Robbins a comprehensive molecular data set is needed to address this question, given how morphologically similar this group is, and Pyrrhura as a whole.”