Proposal (837) to South American Classification Committee
Recognize additional species in the Sedge Wren (Cistothorus platensis) complex
Robbins and Nyári (2014) presented the first molecular-based phylogeography of the Sedge Wren complex (Cistothorus platensis; includes long-recognized South American C. meridae and C. apolinari as species, both embedded within the complex), with a recommendation that at least 9 species be recognized within South America. Understanding relationships within this complex has been obfuscated because of extreme plumage similarities among taxa (19 subspecies; Traylor 1988) and, as far as studied, all but the North American taxon, stellaris, exhibit dialects (see Kroodsma and colleagues, references below).
Because of the plumage and vocal caveats, Robbins and Nyári (2014) primarily relied on genetic data coupled with long-recognized species for defining species limits within the complex. Given that the distinct North American stellaris and Central American elegans are beyond the scope of SACC, this proposal focuses strictly on the proposed new South American species.
Figure 2 in Robbins and Nyári delineated proposed new South American species, clades E-J. When examining that figure, consult the detailed Discussion and Taxonomic Revision Summary sections. Within those clades, southern hornensis is the most distinct in plumage, by having long wings and proportionally short tail (Traylor 1988), song (Kroodsma et al. 2002; xeno canto, Macaulay; note that there are now more material on xeno-canto than when R & N was published), and with the relatively high genetic divergence makes this a straightforward decision, i.e., hornensis should be recognized as a species. If one recognizes hornensis, then one should at least recognize clades F & G as a species (obviously, platensis has priority) and Andean clades H, I & J (aequatorialis has priority) as a species. I consider that a very conservative treatment of the data available.
Thus, for the time being, I recommend that two additional species be recognized and separated from C. platensis in South America: hornensis and aequatorialis. As we suggested in our paper, an appropriate English name for hornensis, given that it is restricted to the southern cone, would be Austral Wren. Given that aequatorialis populations are Andean, that would be an appropriate name for that species.
Alternatively, with the exception of meridae and apolinari, all South American taxa are considered a single species, platensis. Clearly, if the latter is the course taken, there is no change to species limits within the purview of SACC.
KROODSMA, D. 2005. The singing life of birds. Houghton Mifflin Co., New York, New York, USA.
KROODSMA, D. E., W.-C. LIU, E. GOODWIN, AND P. A. BEDELL. 1999a. The ecology of song improvisation as illustrated by North American Sedge Wrens. Auk 116:373–386.
KROODSMA, D. E., J. SÁNCHEZ, D. W. STEMPLE, E. GOODWIN, M. L. DA SILVA, AND J. M. E. VIELLIARD. 1999b. Sedentary life style of Neotropical Sedge Wrens promotes song imitation. Animal Behavior
KROODSMA, D. E., K. WILDA, V. SALAS, AND R. MURADIAN. 2001. Song variation among Cistothorus wrens, with a focus on the Mérida Wren. Condor 103:855–861.
KROODSMA, D. E., R. W. WOODS, AND E. A. GOODWIN. 2002. Falkland Island Sedge Wrens (Cistothorus platensis) imitate rather than improvise large song repertoires. Auk 119:523–528.
ROBBINS, M.B. and A. S. NYÁRI. 2014. Canada to Tierra del Fuego: species limits and historical biogeography of the Sedge Wren (Cistothorus platensis). Wilson Journal of Ornithology 126:649-662.
TRAYLOR, A. M., JR. 1988. Geographic variation and evolution in South American Cistothorus platensis (Aves: Troglodytidae). Fieldiana Zoology New Series 48:1–35.
Mark Robbins, May 2019
Comments from Claramunt: “NO. I think it is premature to split the complex at this point. First, we have no genetic information on the nominate platensis from Buenos Aires. Traylor concluded that platensis and hornensis belong to the same group based on plumage, so what is the evidence that suggest that platensis is more closely allied with the remaining SA populations? At least in a small series at the AMNH, nothing is obvious to me (see photo). Second, character transitions in plumage, morphometrics, and mtDNA do not seem to be fully congruent, which suggest character intergradation and gene flow. We need samples from central Argentina, were hornensis and platensis may meet, to see if they show signs of isolation.
“From left to right: 1) polyglottus (Corrientes), 2) platensis (Buenos Aires), 3) platensis (Bahia Blanca), 4) ssp? (Chubut), 5) hornensis (Tierra del Fuego).“
“Campagna, L., J. JH St Clair, S. C. Lougheed, R. W. Woods, S. Imberti, & P. L. Tubaro. 2012. Divergence between passerine populations from the Malvinas–Falkland Islands and their continental counterparts: a comparative phylogeographical study. Biological Journal of the Linnean Society 106, no. 4 (2012): 865-879.
“A specimen from Valcheta, in Western Prov. Rio Negro had a COI haplotype more similar to haplotypes found in Jujuy (NW Argentinean Andes), and different from those found along the Patagonian Andes, Tierra del Fuego, and the Falklands. This is consistent with the idea that the subspecies platensis is distinct from hornensis and closer to the other SA subspecies but still, it is a single data point and not informative regarding introgression versus isolation.”
Comments from Remsen: “NO. Although I’m sure Mark is right about there being multiple species involved, I think we need to wait for a full analysis of the complex in terms of voice and perhaps a reappraisal of Traylor’s assessment of the contact zone between nominate platensis and polyglottos in Paraguay and NE Argentina, where he concluded from specimens that two major groups interbred freely. Traylor’s concluding sentence in his Abstract:
‘The two groups must be considered a single species because they still interbreed freely in southeastern South America.’
Comments from Pacheco: “NO. Especially because of the statements brought by Santiago, I consider it appropriate to wait for a work that better sheds light on these uncertainties.”
Comments from Bonaccorso: “NO. For me, it does not make sense to name C. hornensis and C. aequatorialis out of C. platensis, and using the name C. platensis for a non-monophyletic group containing all the other subspecies currently in C. platensis. Yes, it is possible that the clades recognized by Robbins and Nyári are all species, but more data is needed.”
Comments from Jaramillo: “YES. I don’t like the idea of kicking the can down the road and hoping for vocal data that may or may not materialize in this decade. We do have some information here, and yes there are missing bits. However, we have to also use some judgement based on experience, existent geographic patterns of speciation, and data from other species in the family. In my opinion, wrens are the new Scytalopus tapaculos. We are just starting on a journey that will clarify that there is ample biodiversity masked in a simplified understanding of the true phylogeny of these critters. We are getting there with the wood-wrens, moving forward with Cistothorus, and it will be likely more complex when we get to House Wrens. We have data on Troglodytes in North America, where two species (hiemalis and pacificus) that were formerly ignored as marginally different subspecies, actually are two sympatric (at least locally) species that separate clearly not only genetically but based on voice, including call notes. The Marsh Wren (Cistothorus palustris) in North America is certainly two different species, although this is not accepted at this time. The two forms, with different songs, vocal repertoire size, and reactions to playback are well studied, and the two can be found in the same marshes in parts of their range. Visually these Cistothorus, and the Troglodytes mentioned above are very similar, and would not stand out in a striking manner if you lined up specimens and took photos. In fact, the photo of the various South American Cistothorus looking so similar is not surprising but expected. This is the problem: these different species look essentially the same, and this is why Traylor’s work did not resolve in an “aha!” moment. You could have done the same with specimens of Scytalopus and not gotten very far in resolving the real relationships between those birds. It took diligent work in Scytalopus, first with voice, and later with molecular data to get at a better resolution of what that genus really looks like. It was also done in stages, with the added complexity that new taxa were being described as the genus itself was being “resolved.” I don’t see why we cannot make chances with these wrens in a similar manner, step by step. Each time a bit closer to resolving the phylogeny of these taxa.
“Yes, it would be nice to have more vocal data, playback experiments, and analysis of where some of these wren taxa may be sympatric. But do we think that these new data will invalidate the molecular data we have here? I don’t think that will be the case. What is more likely to happen is that it will become a tad more complex and maybe other taxa will deem to be split out. But this is a start, and I do not think it will be in error to split these species now. It may not be the full story, and perhaps there will be two steps forward and one step back, but why wait? Science moves incrementally, and sometimes jogs backwards, but here we actually DO have something to work with. I do not see any problem in moving forward and splitting these species out. I think that leaving things as they are retains a less “correct” taxonomy than splitting things out with the caveats that yes there are some missing data. It would be nice to have them, I agree, but they may never come for all we know.”