Proposal (940) to South American Classification Committee

 

 

Recognize Pseudocolaptes johnsoni as a separate species from P. lawrencii

 

Pseuodocolaptes johnsoni was described as a new species by Lönnberg and Rendahl in 1922 based on a specimen reportedly from Baeza, Ecuador (ca. 1800 m on the Eastern slopes of the Andes). Subsequently, Zimmer (1936) found four specimens that matched perfectly Lönnberg & Rendahl’s description of P. johnsoni but collected on the Western slopes of the Andes. The match was so striking that Zimmer (1936) not only concluded that johnsoni inhabits the western slopes but also cast doubts about the provenance of the type specimen, as all other specimens reported from that region are clearly boissonneautii. Zimmer (1936) also made clear that the distinctive plumage of johnsoni cannot be confused with the juvenal plumage of boissonneautii. Zimmer ended up considering johnsoni as a subspecies of P. lawrencii instead, but without providing any evidence other than presumed “closer affinities”.

 

Based on plumage differences and elevational preferences Robbins & Ridgely (1990) suggested that johnsoni deserves species status, a treatment followed by few lists (Ridgely & Tudor 1994, Ridgely & Greenfield 2001, del Hoyo & Collar 2016). A previous SACC proposal based on this evidence was rejected because of lack of additional evidence such as vocalizations: https://www.museum.lsu.edu/~Remsen/SACCprop28.htm

 

A more recent proposal was based on results of playback experiments showing that the song of johnsoni does not elicit any response in lawrencii individuals, suggesting significant vocal differences potentially producing premating isolation (Freeman & Montgomery 2017):

https://www.museum.lsu.edu/~Remsen/SACCprop754.htm

 

The analyses of Spencer (2011) and Boesman (2016) show the differences in song characteristics between johnsoni and lawrencii. If the samples are representative of each taxon, they show well-marked differences:

johnsoni: Song is a high-pitched rattled series of notes slowing into stuttering and ending (always) with a characteristic high-pitched down-slurred note.”

 

 

lawrencii: Song is a number of well-spaced staccato notes (always present unlike johnsoni) followed by a trill, which usually first ascends in pitch and then slightly descends while slowing down in pace.” (Boesman 2016)

 

 

 

New Information:

 

Forcina et al. (2021) revisited the issue of the species status of lawrencii by reanalyzing DNA sequences from a previous study (Derryberry et al. 2011). They claimed that researchers so far have “neglected” the DNA evidence that indicates that johnsoni is a separate species. They found that the single sample of johnsoni showed levels of divergence comparable to those between lawrencii and boissonneautii. In other words, the three lineages diverged nearly simultaneously about 2 million years ago (using mitochondrial clocks; compare to ~ 4 Ma in Derryberry et al. 2011). The analysis could not resolve whether johnsoni is closer to lawrencii or to boissonneautii. They discuss all the evidence accumulated so far, including morphology, vocalizations, and habitat, and conclude that johnsoni should be elevated to species status.

 

Maximum likelihood analysis (Forcina et al. 2021 fig 1)

 

 

Bayesian analysis (Forcina et al. 2021 fig 1)

 

 

Discussion:

The data needed for evaluating the species status of johnsoni has accumulated slowly over decades, a little at a time, mostly due to the rarity of the species. But all pieces of evidence suggest that johnsoni is a distinctive species. It is clearly diagnosable by plumage; it is not a cryptic species by any means. I don’t understand why Forcina et al. claim that this is a case of “cryptic diversity.”

 

Photographs of the type specimen in the Stockholm museum are now publicly available here:

https://www.nrm.se/forskningochsamlingar/zoologi/samlingar/ryggradsdjur/typsamlingfaglar/tattingar/furnariidae/nrm569749.3562.html

And the photographs confirm the original description and, in my opinion, the match between the type specimen and the AMNH series of 4 birds from W Ecuador.

 

Photographs available online of live birds may be a bit confusing because of the artificial variation in color produced by different light conditions and digital adjustments, and the presence of birds in juvenal plumage, but here are what I consider good representatives of adult johnsoni (very similar the AMNH specimens):

 

https://macaulaylibrary.org/asset/178142751?_gl=1*1pz6d24*_ga*NjE4NTUxOTA5LjE2NDQ5NzU5MDk.*_ga_QR4NVXZ8BM*MTY0NzQwNzI3NC4yNS4xLjE2NDc0MDczMjkuNQ..#_ga=2.131747151.1345091137.1647401651-618551909.1644975909

 

https://macaulaylibrary.org/asset/41029281?_gl=1*30cct8*_ga*NjE4NTUxOTA5LjE2NDQ5NzU5MDk.*_ga_QR4NVXZ8BM*MTY0NzQ1Mjg5NS4yNi4xLjE2NDc0NTMwMTQuNDQ.#_ga=2.201353681.1345091137.1647401651-618551909.1644975909

 

In both the holotype and the photos, note the deep rufous tones on back and flanks (versus brown in the other two taxa), no light streaks on the mantle (vs. streaked in boissonneautii), whitish “cheeks” (vs. buffy in lawrencii), dark lower throat (not forming a gular band that is continuous with the light cheeks like in the other two taxa), inconspicuous superciliary stripe (versus thin but well-demarcated stripe in the other two taxa), blackish breast with white rhomboid spots and rest of the belly rufous (versus predominating buffy spots that coalesce to form a light-colored central belly in the other two taxa).

 

The song is clearly distinctive and not recognized by lawrencii in playback experiments (Freeman & Montgomery 2017). For both plumage and vocalizations, a more detailed analysis of geographic variation across the Colombian Andes would have been desirable but I think that the evidence is compelling.

 

Finally, the genetic evidence adds a bit of additional information. But contrary to what the title in Forcina et al. suggests, it doesn’t “untangle” anything. Genetic data for just three individuals do not tell much about species limits. A random sample of three individuals from a single large and old population can produce a tree similar to the one found by Forcina et al. The species delimitation algorithm based on the Poisson Tree Processes (PTP) used by Forcina et al. is basically a mathematical formalization of a genetic divergence threshold/yardstick criterion, in itself a rather weak species delimitation criterion. The method classifies the nodes of the tree into speciation events and coalescent (intraspecific) events based on levels of divergence. It thus formalizes the observation that the three Pseudocolaptes are rather divergent.

 

The recovered topology doesn’t help much either. A strongly supported sister relationship between johnsoni and boissonneautii would have clearly made the case for separating johnsoni from lawrencii, but there were conflicting topologies across methods, and clade support was nil. In sum, the genetic data is consistent with the species status of johnsoni, but the evidence is rather weak.

 

In any case, I think that plumage, songs, and genes together provide sufficient evidence suggesting that johnsoni deserves species-level status and there is not a hint of evidence that suggest that johnsoni is conspecific with lawrencii or with boissonneautii.


Recommendation:

I recommend the treatment of johnsoni as a separate species.

 

Boesman, P. 2016. Notes on the vocalizations of Buffy Tuftedcheek (Pseudocolaptes lawrencii). HBW Alive Ornithological Note 87. In: Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.

Del Hoyo, J., & N. J. Collar 2016. Illustrated checklist of the birds of the world, Volume 2: Passerines. Lynx Edicions, Barcelona, Spain, & BirdLife International, Cambridge, UK.

Forcina, G., P. Boesman, & M. J. Jowers 2021. Cryptic diversity in a neotropical avian species complex untangled by neglected genetic evidence. Studies on Neotropical Fauna and Environment: 1-8. https://doi.org/10.1080/01650521.2021.1915674

Freeman, B. G., G. A. Montgomery. 2017. Using song playback experiments to measure species recognition between geographically isolated populations: a comparison with acoustic trait analyses. Auk. 134(4):857–870.

Spencer, A. 2011. Variation in tuftedcheek vocalizations.  https://www.xeno-canto.org/article/99

Lönnberg, E., & H. Rendahl 1922 A contribution to the ornithology of Ecuador. Arkiv för Zoologi 14(25): 1-87.

Ridgely, R. S. & P. J. Greenfield. 2001. The birds of Ecuador. Vol. I. Status, distribution, and taxonomy. Cornell University Press, Ithaca, New York.

Ridgely, R. S. & G. Tudor. 1994. The bird of South America. Vol. II. The suboscine passerines. University of Texas Press, Austin, Texas.

Robbins, M. B., & Ridgely, R. S. 1990. The avifauna of an upper tropical cloud forest in southwestern Ecuador. Proc. Acad. Nat. Sci. Philadelphia 142: 59-71.

Zimmer, J. 1936. Studies of Peruvian birds, no. 21. Notes on the genera Pseudocolaptes, Hyloctistes, Hylocryptus, Thripadectes, and Xenops. American Museum Novitates 862: 1-25.

 

 

Santiago Claramunt, March 2022

 

 

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Comments from Robbins: “YES for recognizing Pseudocolaptes johnsoni as a species.  As we pointed out in our 1990 paper, we suspected that johnsoni deserved species status based on plumage and elevational differences.  In the original SACC proposal, I voted against recognizing it as a species because of the lack of vocal data.  However, given that Spencer (2011) and Boesman (2016)  have established vocal differences, I now vote to elevate it to species status.  As pointed out by Santiago, I consider the genetic data equivocal.”

 

Comments from Stiles: “YES. As noted by Santiago, genetics, distributions, plumage, and vocalizations all support recognition of johnsoni as a species (the genetic evidence is weakest, but nothing suggests that johnsoni is NOT a distinct species).”

 

Comments from Areta: “YES. Vocal and plumage data support the split. The playback experiments also support this, even when these lack rigor. Genetic data is conflicting, but show a relative deep divergence between lawrencii, boissonneautii and johnsoni. Harvey et al. (2020) recovered a sister relationship (with low support) of boissonneautii and johnsoni with lawrencii sister to them:”

 

Pajarografo Sólido:Users:javierareta:Desktop:Harvey et al 2020 Pseudocolaptes.png

 

Comments from Lane: “YES. Between the distinctive vocalizations and the likelihood that P. lawrencii and P. johnsoni are not sisters, it seems the only reasonable move to separate the two at the species level.”

 

Comments from Pacheco: “YES. Accumulated evidence including genetics, morphology, vocalizations, and habitat support the recommendation of this proposal.”

 

Comments from Bonaccorso: “YES. All the evidence points towards species status. There are distinctive plumage differences between P. lawrencii, P. johnsoni, and P. boissonneautii (still, this level of plumage differences alone does not grant more than subspecies status in other groups). The difference in song is clear, and the genetic differentiation (although from just one specimen per species) is deep. Even if we cannot know the sequence of splits between all three species, which seem to have happened very fast in evolutionary time, the available evidence points to three lineages that have been evolving independently from each other for about 2-4 million years. Also, I know that allopatry is frequently used against granting species status, but I love seeing a clear geographic break between P. lawrencii and P. johnsoni.”