Proposal (114) to South American Classification Committee
Change linear sequence of genera in Ramphastidae
Effect on South American CL: This would alter our linear sequence of genera in the Ramphastidae to reflect the results of molecular phylogenetics.
Background: Our current sequence of genera in the Ramphastidae 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, two data sets based on DNA sequences show a different pattern. Moyle (2004), using mtDNA (cytochrome b) and nuclear DNA (intron 7 of beta fibrinogen), found that Ramphastos was basal to all other genera (100% Bayesian posterior probability, and 100% bootstrap support). The remainder of the genera form two branches: (1) Aulacorhynchus + (Selenidera + Andigena), and (2) Pteroglossus + Baillonius. The support for this branching pattern was strong (94-100% Bayesian posterior probabilities, and 86-100% bootstrap values). Weckstein (2004), using ca. 2500 bp of mtDNA, found the identical pattern for the internal nodes, also with high support values (but did not root his analysis to allow determination of whether Ramphastos was basal). The DNA-DNA hybridization results of Sibley & Ahlquist (1990) are consistent with a basal position of Ramphastos: they found Ramphastos was basal to Aulacorhynchus + Pteroglossus (but these were the only three genera sampled). Nahum et al. (2003), using mtDNA sequence data, found the same branching pattern, with strong support for all nodes except Aulacorhynchus being the sister to (Selenidera + Andigena).
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 need to start with Ramphastos. Then, choice of which branch to start with is more arbitrary, but to create minimum change from an inversion of the traditional sequence, branch "1" above should come next, with the basal taxon Aulacorhynchus first, followed by Andigena and Selenidera. This produces a new sequence as follows:
Although other permutations within the sequence are possible, the key point of the new sequence is to place basal Ramphastos first.
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 genera in any family in our classification.
MOYLE, R. G. 2004. Phylogenetics of barbets (Aves : Piciformes) based on nuclear and mitochondrial DNA sequence data. Molecular Phylogenetics and Evolution 30: 187-200.
NAHUM, L. A., S. L. PEREIRA, F. M. C. FERNANDES, S. R. MATIOLI, AND A. WAJNTAL. 2003. Diversification of Ramphastinae (Aves, Ramphastidae) prior to the Cretaceous/Tertiary boundary as shown by molecular clock of mt DNA sequences. Genetics Molecular Biology 26: 411-418.
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 and Rob Moyle)
Comments from Jaramillo: "YES _ Data are strong, and the new linear sequence reflects this new phylogenetic information."
Comments from Stiles: "YES. The evidence is strong and unequivocal. Incidentally, Moyle's paper also reopens the question of whether to lump Capitonidae into Ramphastidae, a proposal we voted down a while back. The main stumbling block, then as now, was Semnornis, but the level of genetic divergence strongly supports Prum's original proposal of lumping the two families, with Semnornis somewhere within as "incertae sedis". I would support a proposal to recognize Capitoninae and Ramphastinae plus Semnornis as incertae sedis within an expanded Ramphastidae."
Comments from Zimmer: "YES. The evidence seems compelling."
Comments from Nores: "SI; en este caso particular estoy de acuerdo con el nuevo ordenamiento ya que cuenta con un buen conjunto de datos coincidentes que soportan la DNA secuencia."