Presently, the emydine species can be divided into four well-supported, monophyletic groups (Figure 1); listed in order of their date of authorship these are:
Emys Dumeril 1806 - The type species of Emys is the European pond turtle, Emys orbicularis (Linnaeus 1758). Using mtDNA data, Bickham at el. (1996) were the first to suggest that the western pond turtle, Emys marmorata Baird and Girard 1852, Blanding’s pond turtle, Emys blandingii (Holbrook 1838), and E. orbicularis form a monophyletic group. Given this arrangement, Bickham et al. (1996) suggested that all three species could be placed in the genus Emys, pending further support. Since that time, a monophyletic Emys has been strongly supported by two additional molecular-based studies (Lenk et al., 1999; Feldman and Parham, 2002) and an expanded Emys was adopted by Feldman and Parham (2002). However, Holman and Fritz (2001), based on the results of Lenk et al. (1999), suggested the Emys clade be divided into three separate genera: Emys, Actinemys Agassiz, 1857 (for E. marmorata) and Emydoidea Gray 1870 (for E. blandingii). They specifically avoided placing a species without shell kinesis (E. marmorata) into the same genus as taxa with shell kinesis (E. orbicularis and E. blandingii). We disagree with this typological approach, and provide the following arguments in support of a more inclusive Emys.
First, there are multiple examples of turtle genera that display varying degrees of shell kinesis. Two notable examples are mud turtles (Kinosternon) and Palearctic tortoises (Testudo). In fact, shell kinesis can be polymorphic within a single species. For example, the spider tortoise, Pyxis arachnoides, can have a plastron with a well developed hinge or an akinetic plastron (Siebenrock, 1906; Bour, 1981). Additionally, Harding (pers. comm. To JFP) has recorded E. blandingii with akinetic plastra in Michigan. Because shell kinesis is a character that can vary at several taxonomic levels, even within emydine species, we feel it should not be used to split Emys into separate genera.
Second, Feldman and Parham (2002) found that the amount of uncorrected sequence divergence among the three Emys species (5.66-6.33%) overlaps with the genetic distances seen between other congeneric emydines (4.22- 6.09%), but is less than that observed between emydine genera (7.01-9.26%). Although useful as a comparative example, we emphasize that genetic distance alone (i.e, without a phylogenetic justification) should not be an arbiter of taxonomy.
Third, the taxonomy suggested by Holman and Fritz (2001) results in three closely related genera, each with a single living species. This would obscure the undeniably close relationships of E. marmorata, E. blandingii and E. orbicularis. Separate generic names are redundant because Emys species are already distinguished by their specific epithets. Extinct relatives of Emys species exist, but the bulk of Emys research and interest is focused on living taxa. To make the scientific names informative to the majority of workers, we suggest Actinemys and Emydoidea be reserved as subgeneric names for groups that include a living species and its close fossil relatives.
Terrapene Merrem 1820- No taxonomic revision is required for the well-known genus Terrapene. All analyses support the hypothesis that the species of Terrapene represent a natural group with a shared history that is independent of the other emydines.
Clemmys Ritgen 1828- The only species in the genus Clemmys is the type species, Clemmys guttata (Schneider 1792). Although monotypic genera are generally undesirable, it is necessary here because the phylogenetic affinities of C. guttata to other emydine genera are uncertain (Bickham et al., 1996; Burke et al., 1996; Feldman and Parham, 2002). None of the analyses suggest a close affinity to Emys marmorata or Glyptemys.
Glyptemys Agassiz 1857- All analyses agree that the wood turtle, Glyptemys insculpta (LeConte 1829), and bog turtle, Glyptemys muhlenbergii (Schoepff 1801), are each other’s closest relative and are not closely related to Clemmys. Two groups working in parallel (Holman and Fritz, 2001; Feldman and Parham 2002) revised the taxonomy of these species. Unbeknownst to one another, they chose different names for this clade. Feldman and Parham (2002) chose Calemys Agassiz 1857 while Holman and Fritz (2001) chose Glyptemys. The generic revision of Holman and Fritz (2001) was published three months before Feldman and Parham (2002) so Glyptemys is the appropriate, valid name. We would like to thank James Harding, Phillip Spinks and Patricia Holroyd for providing helpful suggestions.
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