Molecular Systematics of Map Turtles (Graptemys): A Comparison of Mitochondrial Restriction Site Versus Sequence Data

Analyses of mitochondrial DNA (mtDNA) restriction sites and sequences were used to estimate phylogenetic relationships in the emydid turtle genus Graptemys. We compared resolution and concordance among four mtDNA data sets: (1) restriction sites, (2) cytochrome b sequences (380 base positions [bp]), (3) control region sequences (344 bp), and (4) combined (cytochrome b and control region) sequences. Five of the 12 currently recognized species could not be distinguished on the basis of restriction sites. Cytochrome b sequences provided even less phylogenetic information, whereas control region sequences identified all taxa. Bootstrap consensus trees for the restriction site and control region sequence data resolved three monophyletic clades: a pulchra group, a pseudogeographica group, and the basal G. geographica. Of the four data sets, the control region offered the greatest resolution with respect to species identification and phylogenetic information. However, a character congruence approach, combining both sequence and restriction site characters, significantly bolstered bootstrap support for the major clades and enhanced phylogenetic resolution within them. Sequence divergence estimates (restriction sites: 0.0–3.2%; cytochrome b: 0.0–1.5%) for Graptemys are among the lowest values reported for a generic-level comparison involving vertebrates. These findings are discussed in light of recent drainage isolation events along the Gulf of Mexico and a proposed slow rate of mtDNA evolution in turtles.