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.”
Comments from Pérez-Emán: “NO. As I indicated in Proposal 552, it is risky to define subfamily level taxonomy based on monophyletic groups resulting from DNA analyses. Although I agree this is a powerful tool, I am concerned about the stability of monophyletic groups with increase taxon sampling and the use of different molecular characters. For example, in this particular case, comparing Lerner & Mindell (2005) results with those of Griffiths et al. (2007), studies with similar number of characters but different markers, node support for the proposed subfamilies is different. In fact, the phylogenetic relationship of Elanus is not resolved at all (see Fig. 2 in Lerner & Mindell (2005)). Thus, if we had only this information (a nice study with good taxon and character sampling), what would be our proposal at the level of subfamily? Additional information based on different sets of characters, if congruent with this particular hypothesis, would provide with a potential more meaningful definition of the subfamily category.”
Comments from
Cadena: “YES, but not
strongly convinced (see comments under proposal 552).”
Comments
from Jaramillo: “YES. Seems uncontroversial to me other than in the
point of whether we use the subfamily division, and if so, how to we move to
other groups that require similar treatment.”