Proposal (247) to South American Classification Committee
Eliminate the genus Platycichla and place P. leucops and P. flavipes in Turdus
Background: Systematists have long questioned whether the thrush genus Platycichla should be recognized as distinct with respect to the large and cosmopolitan genus Turdus. For example, Ridgely and Tudor (1989) noted that Platycichla was named solely because it is smaller than most Turdus, and suggested that the two genera should probably be merged considering their similarities in plumage, vocalizations, and behavior.
New data and analysis: Two recent phylogenetic studies based on mitochondrial DNA sequence data demonstrate conclusively that Platycichla is nested within the genus Turdus, implying the two genera should be merged in order to make Turdus monophyletic. Based on complete cyt b and ND2 sequences, Klicka et al. (2005) found that Turdus is paraphyletic but forms a well supported clade with the addition of three mostly monotypic genera (Platycichla, Nesocichla, and Cichlherminia). Although Platycichla was clearly found to be nested within Turdus, its exact phylogenetic position was not determined owing to sparse taxon sampling; in addition, only one of its constituent species (P. leucops) was sampled. Voelker et al. (2006) presented analyses of cyt b, ND2, and ND3 sequences with much more complete taxon sampling: they included 60 of the 65 species of Turdus, in addition to the two species of Platycichla, and several other thrush genera whose systematic position had been contentious. Their results confirmed those of Klicka et al., showing that Turdus is not monophyletic with respect to Platycichla: the two species in the latter genus are part of a well-supported clade formed by mostly South American Turdus taxa. Voelker et al. further showed that the two species of Platycichla are not each other's closest relatives; a tree forcing the monophyly of the genus was significantly less likely than unconstrained trees. The latter result is consistent with differences in nesting biology between the two species noted by Londo–o (2005).
Recommendation: I believe the available data leave no doubt that Platycichla is not a distinct genus with respect to Turdus and that it is not even a monophyletic group. Thus, I recommend a YES vote to get rid of Platycichla and to rename its two constituent species as Turdus leucops and T. flavipes. (Because Turdus has priority over Platycichla, the latter genus needs to be eliminated.)
Klicka, J., G. Voelker, & G. M. Spellman. 2005. A molecular systematic revision of the "true thrushes" (Turdinae). Molecular Phylogenetics and Evolution 34: 486-500.
Londo–o, G.A., 2005. A description of the nest and eggs of the Pale-eyed Thrush (Platycichla leucops), with notes on incubation behavior. Wilson Bulletin 117: 394-399.
Voelker, G., S. Rohwer, R. C. K. Bowie & D. C. Outlaw. 2007. Molecular systematics of a speciose, cosmopolitan songbird genus: defining the limits of, and relationships among, the Turdus thrushes. Molecular Phylogenetics and Evolution 42: 422-434.
C. Daniel Cadena, November 2006
Comments from Remsen: "YES. Clearly, burden-of-proof now falls on anyone claiming that Platycichla is not embedded within Turdus."
Comments from Stiles: "YES. The various citations clearly indicate that Platycichla cannot stand as a genus unless one splits up Turdus into an uncertain number of mini-genera, which would serve no useful purpose for elucidating relationships. Also worth noting that unless I'm mistaken, only one of the two species of Platycichla has been sequenced and there is thus no explicit evidence that the two are sister species in any case."
Comments from Jaramillo: "YES - Data are clear that Platycichla is nested within Turdus. Also, results in Voelker et al. 2007 show that Platycichla flavipes and P. leucops are not sisters."
Comments from Robbins: "YES. Recently published molecular data demonstrate that Platycichla is embedded within Turdus; hence, I vote yes for subsuming this genus within Turdus."
Comments from Nores: "YES. Tanto desde el punto de vista molecular, como se–alado por Cadena, como del punto de vista morfol—gico no parece haber dudas de que Platycichla no difiere de Turdus."
Comments from Pacheco: "YES. Em verdade, tais resultados ratificam o que est‡ delineado desde Ridgway (1907). Peter Clement in Thrushes (Princeton 2000) escreveu para "Platycichla: Two species restricted to South America. They are similar to (and poorly separated from) the Turdus thrushes in size, shape and structure."