Recognize Trogon mesurus as a separate species from Trogon melanurus (2)

Proposal (#380) to South American Classification Committee

Recognize Trogon mesurus as a separate species from Trogon melanurus (2)

Effect on SACC: This would treat an existing species, Trogon melanurus, into two species.

Background: Our current SACC note is as follows:

12. <?Hellmayr 1929> considered the South American subspecies australis as a separate species from Middle American Trogon massena; Zimmer (1948) suspected that australis might actually be a subspecies of T. melanurus. The subspecies macroura of northwestern Colombia and Panama was formerly (e.g., REF<?Hellmayr 1929>) considered a species separate from Trogon melanurus, and it may deserve recognition as a separate species (Zimmer 1948). Ridgely & Greenfield (2001) considered mesurus of western Ecuador and northwestern Peru to be a separate species from T. melanurus; SACC proposal to recognize this split did not pass because of insufficient published data. Genetic data (DaCosta & Klicka 2008) indicate that melanurus may be paraphyletic with respect to T. massena and T. comptus. Proposal needed.

See SACC proposal 51 for a summary of previous arguments pro and con. A one-sentence summary of the previous arguments might be although mesurus differs as much from melanurus as the latter does from massena, the vocal differences have not been adequately quantified or documented.

New information: DaCosta & Klicka (2008) published a gene-based phylogeny of the genus that included samples of cis-Andean melanurus (9) from Guyana, Bolivia, e Ecuador, and Peru, and trans-Andean mesurus (2) from nw Ecuador. They sampled 1 mitochondrial gene, ND2, and 1041 base pairs, of which 557 were phylogenetically informative. They did not sample trans-Andean macroura, the subspecies of melanurus from N Colombia and W Panama.

They found that the two groups fell into three clades: (1) cis-Andean melanurus (with substandard support for a sister relationship to T. comptus), and (2) trans-Andean mesurus and T. massena (99% maximum likelihood bootstrap, 100% Bayesian support. See Prop. 378 for tree.

Analysis and Recommendation: With genetic support from only a single, mitochondrial gene as the basis for the relationship, one could argue that the tree is only a gene tree, not a species tree, or that incomplete lineage-sorting confounds the result. However, with the qualitative vocal data, I think that published evidence is sufficient for a change in species limits, so I tentatively recommend a YES.

Literature Cited:

DaCOSTA, J. M., AND J. KLICKA. 2008. The Great American Interchange in birds: a phylogenetic perspective with the genus Trogon. Molecular Ecology 17: 1328-1343.

Note on English names: Ridgely & Greenfield (2001) coined “Ecuadorian Trogon” for mesurus, leaving Black-tailed for melanurus, and this was followed by Gill & Wright (2006). I think that represents a degree of establishment that justifies starting with them as “status quo” if the proposal passes.

Note added 4/10: The subspecies macrourus of Panama and NW Colombia has not been analyzed genetically. It lacks the pale iris of mesurus, and despite its trans-Andean distribution, is likely closer to cis-Andean melanurus. Further data obviously needed, but this proposal refers strictly to mesurus.

Van Remsen, November 2008

Comments from Zimmer: “YES, for reasons summarized by Van. I also agree that “Ecuadorian Trogon” and “Black-tailed Trogon” should be retained as English names.”

Comments from Robbins: “YES, for recognizing mesurus as a species and using English names suggested by Ridgely and Greenfield.”

Comments from Stiles: “YES, for the same reasons as in 380. Since previously noted morphological and vocal differences coincide with genetic differences of a magnitude consistent with species status, the burden of proof shifts to those who would maintain them in a single species. Once again, Van’s English names seem OK with me.”

Comments from Nores: “NO. Aunque por el análisis molecular parece claro que son dos especies diferentes, el hecho de que hay soporte genético para un solo gen mitocondrial puede estar indicando de que se trata de un árbol del gen y no de un árbol de las especies, como mencionado por Remsen. Además, las diferencias morfológicas son mínimas y el canto, de acuerdo a Ridgely y Greenfield, es similar siendo formado por cortas series, enves de una sola larga. A raiz de esto, quiero mencionar nuevamente algo que dije en la propuesta 49 y que ya casi me había olvidado: “Separar especies por suaves diferencias en el canto no me parece bien, como ya lo expresé en el caso de Rhynchotus rufescens maculicollis. Recientemente estuve en el noreste de Brasil y me llamó la atención lo diferente que son los cantos de algunas subespecies de allí con respecto a las poblaciones del sur de Sudamérica. Por ejemplo, Thraupis sayaca tiene un canto mucho más potente y más variado que las razas del sur, y Turdus rufiventris emite un llamado permanente que nunca se lo escuché a la subespecie de esta latitud. Otro ejemplo del sur es Vanellus chilensis, del cual la raza del sur de Argentina y Chile emiten un canto bastante diferente (parece un loro) que la raza que habita el norte y centro de Argentina. Tanto es así que muchas personas (no ornitólogas) me preguntan qué a que se debe que las aves del sur cantan tan distinto Esto no significa para mí que haya que elevar las subespecies a especies."

Comments from Stotz: “YES. I think the interposition of massena in the tree between the cis and trans Andean populations along with the morphological differences and vocal differences argue for this change. I also favor the Ecuadorian Trogon as a name for this taxon.”

Comments from Jaramillo: “YES – Song, morphology and genetics all line up to clarify the relationship here. Yes to English names, Ecuadorian and Black-tailed.

Comments from Pacheco: "YES. Dados genéticos, de vocalização e morfologia dão bom suporte a proposta.”