Taxon of the Week #3: Rana

The taxon that has been chosen to receive the coveted Taxon of the Week spot today is the frog genus Rana. Rana is a large primarily Holarctic genus of frogs, and probably the inspiration for most depictions of frogs in the world (see the page on Wikipedia and linked pages for images). Well-known species are the edible frog (Rana × esculenta - actually not a true species but a hybrid) and the European common frog (Rana temporaria).

I thought I'd look up the info on Rana over lunchtime. Pretty soon, my head was swimming. The genus Rana has been hit with two major investigations in recent years, both of which have received some frosty responses. Frost et al. (2006) in their investigation of the 'Amphibian Tree of Life' divided Rana between more than fifteen smaller genera to remove its previous paraphyly (for instance, the above-mentioned Rana esculenta would become Pelophylax esculentus). As happens with any wholesale name change, there has been quite a bit of outcry at the idea of having to update the filing systems. Also, a number of authors have felt that the number of taxa sampled by Frost et al. was not enough to inspire confidence in their results. The review by Wiens (2007) was particularly vitriolic - the scientific equivalent of attempting to hold the subject down and kick them repeatedly in the teeth. Smith and Chiszar (2006) have suggested the more mollifying approach of treating Frost et al.'s various genera as subgenera, though unless one was willing to accept a paraphyletic genus this would also require sinking some well-established genera such as Staurois within Rana. Division of the genus Rana was also supported by Che et al. (2007).

The other cause of debate was perpetrated by Hillis & Wilcox (2005), who investigated the phylogeny of New World species of 'Rana' (most of which would belong to Lithobates in the Frost et al. system). The problem came when Hillis & Wilcox suggested a whole series of subgeneric taxa for nested groups of species that they defined according to the rules of the PhyloCode, but also allowed for use under the ICZN as subgenera. Debate promptly exploded about whether Hillis & Wilcox's names were validly published and usable (Dubois, 2006, 2007; Hillis, 2007). Compared to this argument, Frost et al.'s division appears quite simple. I may return to this in a later post, if my brain doesn't implode first. Check out the Dubois (2006) paper in particular - Dubois thinks that the answer to our problems is to make the ICZN more complicated. No. Thank. You.

REFERENCES

Che, J., J. Pang, H. Zhao, G.-F. Wu, E.-M. Zhao & Y.-P. Zhang. 2007. Phylogeny of Raninae (Anura: Ranidae) inferred from mitochondrial and nuclear sequences. Molecular Phylogenetics and Evolution 43 (1): 1-13.

Dubois, A. 2006. New proposals for naming lower-ranked taxa within the frame of the International Code of Zoological Nomenclature. Comptes Rendus Biologies 329 (10): 823-840.

Dubois, A. 2007. Naming taxa from cladograms: A cautionary tale. Molecular Phylogenetics and Evolution 42 (2): 317-330.

Frost, D. R., T. Grant, J. Faivovich, R. H. Bain, A. Haas, C. F. B. Haddad, R. O. de Sá, A. Channing, M. Wilkinson, S. C. Donnellan, C. J. Raxworthy, J. A. Campbell, B. L. Blotto, P. Moler, R. C. Drewes, R. A. Nussbaum, J. D. Lynch, D. M. Green & W. C. Wheeler. 2007. The amphibian tree of life. Bulletin of the American Museum of Natural History 297: 1-370.

Hillis, D. M. 2007. Constraints in naming parts of the Tree of Life. Molecular Phylogenetics and Evolution 42 (2): 331-338.

Hillis, D. M., & T. P. Wilcox. 2005. Phylogeny of the New World true frogs (Rana). Molecular Phylogenetics and Evolution 34 (2): 299-314.

Smith, H. M., & D. Chiszar. 2006. Dilemma of name-recognition: why and when to use new combinations of scientific names. Herpetological Conservation and Biology 1 (1): 6-8.

Wiens, J. J. 2007. Review: The Amphibian Tree of Life. Quarterly Review of Biology 82: 55-56.