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.
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.”