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:
Aulacorhynchus
Pteroglossus
Baillonius
Selenidera
Andigena
Ramphastos
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:
Ramphastos
Aulacorhynchus
Andigena
Selenidera
Pteroglossus
Baillonius
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.
Literature Cited:
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)
____________________________________________________________________________________________
Voting chart for SACC proposals
100-218
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."