Proposal (115) to South American Classification Committee
Change linear sequence of species in Ramphastos
Effect on South American CL: This would alter our linear sequence of species in Ramphastos to reflect the results of molecular phylogenetics.
Background: Our current sequence of species in the Ramphastos is the traditional one (e.g., Meyer de Schauensee 1970) as follows:
This sequence is perpetuated by historical momentum rather than phylogenetic analysis. I suspect that the rationale, which I cannot find, was based on the reasonable assumption that the genus with the smallest, shortest-billed species, Aulacorhynchus, was the most barbet-like and thus was the most "primitive" in the family, and Ramphastos, the genus with the largest, least-barbet-like species, was the most "recent."
New information: Regardless of whatever rationale was behind the traditional sequence, Weckstein (2004), using ca. 2500 bp of mtDNA, found the following:
(1) toco was basal to all other species (78% Bayesian probability; 80% bootstrap value)
(2) the remaining species were divided into two clades composed of the (a) smooth-billed yelpers (tucanus/cuvieri + swainsonii/ambiguus) (99% Bayesian probability/99% bootstrap value), and (b) the smooth-billed croakers (culminatus-vitellinus-ariel, brevis, sulfuratus) (79%/56% ). Within the croaker group, support for any particular branching pattern was not strong.
Analysis: Assuming that our classification should attempt to reflect phylogeny wherever possible, we need to change our sequence to conform to the convention of listing basal taxa first. To do this, we essentially have to invert it, but start, of course, with toco, as follows:
Other permutations are possible, but this one sticks as close as possible to an inversion of the traditional one and arranges putative sister taxa or close relatives in a conventional north-to-south sequence.
Recommendation: I vote YES on this because it represents one of the few cases in which we have a good data-set to support the sequence of species in any genus in our classification.
WECKSTEIN, J. D. 2004. Biogeography explains cophylogenetic patterns in toucan chewing lice. Systematic Biology 53: 154-164.
Van Remsen, April 2004 (in consultation with Jason Weckstein)
Comments from Jaramillo: "YES _ Data are strong, and the new linear sequence reflects this new phylogenetic information. The recovery of a yelper clade and croaker clade is especially interesting, another situation where voice is phylogenetically more important as a character than plumage pattern."
Comments from Stiles: "YES. Again, the evidence favoring a change in sequence is much stronger than that upon which the "traditional" sequence was based. Just to muddy the waters a bit, I might note that I strongly suspect that swainsonii merits species status (separate from ambiguus) BUT including the geographically intermediate form, abbreviatus, with swainsonii. The arguments are given in BBOC 119:120-121, though a detailed analysis was not presented (insufficient real data!). I mention it mainly to see if anyone might be interested in following this one up, or has more detailed information on this group, especially the east-slope ambiguus itself (soft-part colors, more on voice - ambiguus voice sounds like a less-structured version of that of swainsonii-abbreviatus, somewhat approaching the tucanus group)."
Comments from Zimmer: "YES. The evidence seems compelling, and the proposed west-to-east sequence makes sense."
Comments from Stotz: "(No). I can see moving toco to the front, but why not leave all the rest in their current position? Note that in principle I am opposed to attempting to use linear order to give phylogenetic information. This is a good case in point. The current order in fact is consistent with the known tree for this group; only the convention of basal first requires changing that order. But for anybody not in on this conversation, this new order seems just as arbitrary as the last order. I favor alphabetical order within the hierarchy, so toucans would by alphabetical by genus, followed by alphabetical within the genera and we'd be done. Anybody who wanted to know the relationships within the genera or between genera would have to go to the papers describing taxonomic work done. But they have to do that anyway. As I said, without access to this discussion could anybody tell anything useful about the relationships of taxa based on our linear order? However, as long as we allegedly are providing info through order, these changes (except for my opening complaint here) are better than most current information supporting our sequences."
Comments from Nores: "NO; yo pienso que un solo trabajo molecular no es un "good data-set" suficiente como para cambiar la secuencia actual. Pienso que todos los miembros del "committee" estamos muy influenciados por los análisis moleculares. Yo esperaría que por lo menos haya dos trabajos con resultados similares. ņQué haríamos si aparece otro trabajo que difiere del primero? ņVolveríamos a cambiar la secuencia? Recientemente he tenido la oportunidad de revisar un trabajo en el cual los autores mostraban un nuevo ordenamiento filogenético de las especies que según ellos era mejor y mostraba grandes cambios que dos previos trabajos moleculares.
"Pienso que antes que cambiar la secuencia sería importante analizar el status de varias especies que hasta recientemente y aún hoy están consideradas válidas (citreolaemus, culminatus, cuvieri y swainsonii) por ejemplo en Birds of Colombia (Hilty and Brown) y Birds of Venezuela (Phelps and Mayr)."