Is Chinemys megalocephala FANG, 1934 a valid species? New insights based on mitochondrial DNA sequence data

An 871 bp long fragment of the mitochondrial cytochrome b gene was used for reconstructing the phylogeny of turtles of the genus Chinemys. C. nigricans is clearly differentiated from the other two species of that genus, separated by a sequence divergence of approximately 4.3 to 5.7 %. No differences were detected between two C. megalocephala and two C. reevesii. However, considerable sequence divergence ranging 1.6 to 1.7 % was found among C. reevesii as an additional sequence obtained from GenBank differed significantly from our own data. It might be that this finding is due to sequencing errors of the GenBank sequence. Three hypotheses are formulated to explain the identical sequence data of C. megalocephala and C. reevesii: (a) Both nominal species are identical and C. megalocephala is just a “diet variant” of C. reevesii as believed earlier based on morphology. (b) The identity of mtDNA sequence data in C. megalocephala and C. reevesii is the result of introgressive hybridization of two closely related species. (c) C. megalocephala originated from hybridization of only distantly related species, as known for several chelonians. In (b) and (c), the maternal parent or ancestor would be C. reevesii as mitochondrial DNA is inherited exclusively in a maternal line.