Phylogenetic implications of karyotypic variation in the Batagurinae (Testudines: Emydidae)

Abstract

The present study examined karyotypes of 16 genera and, along with previous reports, chromosomal data are now available for 18 of the 23 recognized batagurine genera. There are no karyotypic data available for the members of McDowell's (1964) Hardella complex. The Batagur, Heosemys and Geoemyda complexes retain the hypothesized primitive karyotype for the subfamily (2n=52). All the genera in these three complexes have been examined except Batagur and Annamemys. The Orlitia complex is karyotypically distinct with 2n=50 and the NOR located terminally on a large microchromosome. The genus Malayemys inclusion in the Batagur complex is not supported. Malayemys is characterized by a 2n=50 karyotype, with the NOR located interstitially on a large microchromosome. The Malayemys complex is erected to contain this genus at a point intermediate between the Orlitia complex and the subfamily Emydinae. Malayemys and the emydines are karyotypically indistinguishable. The Neotropical genus Rhinoclemmys (Geoemyda complex) differs only slightly from the primitive batagurine karyotype in the position of the NOR. The species R. funerea and R. punctularia further differ in possessing one less metacentric macrochomosome. An interesting situation involves two subspecies of R. punctularia. The nominate subspecies is characterized by a 2n=56 karyotype, while R. p. melanosterna reportedly has a 2n=52 karyotype. Such a difference is interpreted as indicative of genetic differentiation between the two forms of a magnitude inconsistent with considering them as conspecific. Taken together with zoogeographic considerations, the karyotypic difference between the forms R. p. punctularia and R. p. melanosterna seem sufficient to warrant species distinction for R. melanosterna as previously suggested by Pritchard (1979b).