Molecular phylogeny and divergence of the map turtles (Emydidae: Graptemys)

The map turtles (genus Graptemys) comprise a morphologically diverse clade that forms a major component of the southeastern US hotspot of chelonian diversity. Map turtles have experienced both recent and rapid diversification resulting in long-standing uncertainty regarding species boundaries and phylogenetic relationships within the genus as well as timing of their divergence. We present a phylogeny for the group that includes geographically representative sampling for all described species and subspecies. We make use of an empirical prior on rates of molecular evolution to estimate divergence times with a molecular clock under a coalescent framework. Together, the phylogeny and divergence time estimates suggest that diversification has been both more recent and more rapid than has so far been suspected. We provide a well-supported evolutionary framework for Graptemys that is necessary for understanding map turtle diversity, biogeography, and for conservation of this threatened clade of turtles.