Competing generic concepts for Blanding’s, Pacific and European pond turtles (Emydoidea, Actinemys and Emys)—Which is best?

Abstract

We review competing taxonomic classifications and hypotheses for the phylogeny of emydine turtles. The formerly recognized genus Clemmys sensu lato clearly is paraphyletic. Two of its former species, now Glyptemys insculpta and G. muhlenbergii, constitute a well-supported basal clade within the Emydinae. However, the phylogenetic position of the other two species traditionally placed in Clemmys remains controversial. Mitochondrial data suggest a clade embracing Actinemys (formerly Clemmys) marmorata, Emydoidea and Emys and as its sister either another clade (Clemmys guttata + Terrapene) or Terrapene alone. In contrast, nuclear genomic data yield conflicting results, depending on which genes are used. Either Clemmys guttata is revealed as sister to ((Emydoidea + Emys) + Actinemys) + Terrapene or Clemmys guttata is sister to Actinemys marmorata and these two species together are the sister group of (Emydoidea + Emys); Terrapene appears then as sister to (Actinemys marmorata + Clemmys guttata) + (Emydoidea + Emys). The contradictory branching patterns depending from the selected loci are suggestive of lineage sorting problems. Ignoring the unclear phylogenetic position of Actinemys marmorata, one recently proposed classification scheme placed Actinemys marmorata, Emydoidea blandingii, Emys orbicularis, and Emys trinacris in one genus (Emys), while another classification scheme treats Actinemys, Emydoidea, and Emys as distinct genera. The inclusion of Actinemys in the same taxon as Emydoidea + Emys is unacceptable under a phylogenetic classification framework because there is evidence for the non-monophyly of this clade. Moreover, Actinemys, Emydoidea, and Emys are morphologically highly distinct. Their morphological divergence exceeds by far the differences that typically occur among species of the same genus, so that a continued usage of the distinct genera Actinemys, Emydoidea and Emys is recommended.