Proposal (553) to South American Classification Committee
Add subfamilies to Accipitridae
Effect on SACC: This proposal would divide the South American
representatives of the Accipitridae into three subfamilies.
Background & new information: Although many classifications have used
subfamily designations in the Accipitridae, SACC has not, as explained in the
SACC footnote excerpt below. New
data, as also explained in the footnote, however, confirm that the Accipitridae
contains several deeply divergent lineages that could be designated as
subfamilies:
Lerner & Mindell (2005) found that the
Accipitridae consisted of fourteen principle lineages, which they designated
with subfamily rank. Griffiths et al. (2007) found that the family consists of eight
major lineages, which they designated using tribe, subtribe, and infratribe
ranks; none of Peters (1931) subfamilies was found to be monophyletic. SACC proposal
needed to consider subfamily structure.
Here is a summary tree from Griffiths et al. (2007):
Here is their tree using maximum likelihood, which is easier
to use in examining relative levels of divergence (but more difficult to read
here – I recommend looking at the pdf of their paper):
Here is their appendix on recommended classification, but
note that their scheme treats Secretarybird and Osprey as subfamilies, whereas
we treat the latter as a separate family.
So, to maintain the level of our ranks, convert their Tribe groups to
Subfamily rank.
The Lerner & Mindell (2005) trees are basically the
same, but with different interpretations of group ranks and slightly weaker
taxon sampling.
Discussion: We have no formal definition of “subfamily” beyond the
obvious, namely monophyletic groups within a family. Under “Taxonomy” in our Introduction, we have the following
statement: “Most traditional subfamilies are
omitted unless supported by multiple independent data sets that mark major,
deep branches within a family.”
Personally,
I increasingly see the value in emphasizing strong within-family monophyletic
groups with subfamily rank, particularly as confidence increases with better
and better DNA-based data. Not
only is it helpful to have official names for such groups, but also the names
emphasize monophyletic groupings.
We have no objective definition of “major, deep”, but no one else does
either; in fact, objective definitions of any higher rank are largely
nonexistent. Regardless of rank,
marking the well-supported nodes with names increases the information content
of classification.
So far,
we have not used tribes in SACC, and that is a separate issue that we should
discuss. For the purposes of this
proposal, I recommend we stick to subfamilies. Besides, in this case the groupings get messier inside
Accipitrinae.
With
that preamble, I think the data sets of Lerner & Mindell (2005) and Griffiths
et al. (2007) indicate that the family contains at least three major divisions:
(1) Elaninae (Elanus and Gampsonyx); (2) Gypaetinae (for us only
Leptodon, Elanoides, and Chondrohierax);
and (3) Accipitrinae (for us, everything else). I would agree with Griffiths et al.’s interpretation of the
branching pattern that three subfamilies are the way to go, with other groups relegated
to tribe rank.
Note
that we have already adopted the Griffiths et al. (2007) classification in
terms of sequence of genera (proposal 384), so this proposal is just adding subfamily
structure, as outlined above, to the existing sequence of genera.
Recommendation: I recommend a YES on this. The results of Griffiths et al. are solid, and also
consistent with an earlier, independent data-set (as well as other studies with
better taxon sampling within the subfamilies, such as Raposo do Amaral et al.’s
analyses of the buteonine genera.
My only concern is that additional gene sampling might alter the
branching pattern, as it did for the plovers (see proposal 551), but that same concern could be hurled at virtually
every study on which we have based our classification so far.
Literature:
GRIFFITHS,
C. S., G. F. BARROWCLOUGH, J. G. GROTH, AND L. MERTZ. 2007. Phylogeny,
diversity and classification of the Accipitridae based on DNA sequences of the
RAG-1 exon. J. Avian Biology 38: 587-602.
LERNER,
H. R. L., AND D. P. MINDELL. 2005. Phylogeny of eagles, Old World vultures, and
other Accipitridae based on nuclear and mitochondrial DNA. Molecular
Phylogenetics and Evolution 37: 327-346.
Van Remsen,
October 2012
Comments from Zimmer: “YES.
I agree with Van that there is
value in emphasizing strong, within-family monophyletic groups with formal
names. The waters may be muddied
somewhat if we also adopt Proposal #560 (recognizing “Tribes” as a level in our
classification), but, overall, I think this is the way to go. As for the Accipitridae, the three
major divisions as interpreted by Griffiths et al constitute a sensible first
step, and I think we should adopt those subfamilies into our classification.”
Comments from Stiles:
“YES. These three subfamilies seem
reasonable and taxonomically equivalent.
However, from there on down things get dicier. In Accipitrinae one could easily recognize 10-12 tribes;
hence I’d be a bit reluctant to plunge into tribes - and the finer the
subdivisions used, the more likely that further work will require revision!”
Comments from Nores: “NO, it doesn’t seem necessary.”
Comments from Robbins: “NO - see comments under proposal # 552.”