Evolutionary Relationships between Graptemys Turtles in the Mississippi River

Abstract

The Mississippi River contains widely recognized species of freshwater turtles belonging to the genus Graptemys that are closely related to other species found outside of the Mississippi. In particular, G. pseudogeographica, G. p. kohnii, G. ouachitensis, and G. o. sabinensis are of interest. DNA from populations outside of the Mississippi River has shown that other Graptemys species form monophyletic groups and produce resolved evolutionary data. However, tissue samples taken and sequenced from the aforementioned Graptemys turtles in the Mississippi River drainage system do not form a clear monophyletic clade of recognized species, as seen in sister taxa outside of the Mississippi. Instead, samples from this drainage are paraphyletic and scattered throughout the phylogeny. Sequences across four nuclear genes, RELN, BDNF, NB17483, and HNFAL were obtained from individuals belonging to G. pseudogeographica, G. ouachitensis, G. o. sabinensis, and G. p. kohnii. Three of the four nuclear genes were used to construct individual phylogenies and concatenate new data with previous data in a new, comprehensive gene tree. Individual gene trees provided low resolution and concatenated phylogenies produced paraphyletic groups in the Graptemys tree of life. Monophyletic clades are documented outside of the Mississippi River drainage system, but did not emerge in phylogenies generated by MrBayes. Instead, paraphyletic groups persisted, indicating a need for further investigation for more support and to investigate why paraphyletic groups are predominant in the Mississippi River. The resulting data and analysis provided further information for understanding the pattern and process of evolutionary history and diversification in turtles of the southeastern United States, but more research is needed to strengthen current data indicating paraphyletic relationships among Graptemys species located in the Mississippi River drainage system.