Resurrect Rhynchospiza for South American “Aimophila”
Effect on South American CL: This would change the genus for two species in the SACC list from Aimophila to Rhynchospiza.
Background: Our current Note is as follows:
The genus Aimophila is widely suspected of being polyphyletic (Ridgway 1901, Storer 1955b, Wolf 1977). Aimophila stolzmanni was formerly (e.g., Hellmayr 1938, Meyer de Schauensee 1970) placed in a monotypic genus, Rhynchospiza, but most recent authors (e.g., Ridgely & Tudor 1989) have followed Paynter (1967, 1970a) in merging this into Aimophila. DaCosta et al. (2009) have confirmed that Aimophila is polyphyletic and that the South American taxa are not members of true Aimophila; they recommended resurrection of Rhynchospiza, which would also include stolzmanni’s sister species, A. strigiceps. SACC proposal badly needed.
New information: DaCosta et al. (2009) sequenced two mitochondrial genes (cyt-b, NADH) for all members of Aimophila as well as many taxa in related genera. Their results confirmed the long-held suspicion that Aimophila is polyphyletic. The only true Aimophila are three Middle American species. Chesser et al. (2010) have followed their recommendations in resurrecting Peucaea (including “mysticalis” [sic] throughout their text) for one group of sparrows formerly in Aimophila and transferred another species to Amphispiza. This leaves the two South American species, stolzmanni (“stolzmani” [sic] in their Fig. 3; see below) and strigiceps, which DaCosta et al. recommended placing in Rhynchospiza Ridgway, 1898, evidently the oldest genus available for the two.
Analysis and recommendation: The genetic data show strong support for a sister relationship between stolzmanni and strigiceps, which also makes sense in terms of biogeography and plumage similarities. The thicker-than-normal bill of stolzmanni likely reflects a pattern of seed-eating birds in arid areas have over-sized bills because seeds in such climates tend to be large and tough to crack. True Aimophila are in a completely different part of the emberizid tree – see their Fig. 3 below – sorry for the fuzziness of the screen grab. Although support is strong for the inclusion of the two South American species in a clade that includes the Peucaea group, that group also includes the Myospiza group of Ammodramus sparrows and Arremonops. Therefore, resurrection of Rhynchospiza seems the simplest and wisest solution, as recommended by DaCosta et al. Therefore, I recommend a YES on this one.
DaCOSTA, J. M., G. M. SPELLMAN, P. ESCALANTE, AND J. KLICKA. 2009. A molecular systematic revision of two historically problematic songbird clades: Aimophila and Pipilo. J. Avian Biology 40: 206-216.
Van Remsen, August 2010
Comments from Stotz: “YES. The North American committee has been redoing this section of the Emberizidae, and this fits in with that approach. It would be very difficult to imagine a basis for continuing to maintain Rhynchospiza within Aimophila, lumping them into a broad genus representing the clade at the top of the tree in the proposal would produce a large very heterogeneous group.”