Three's Company: Observations of a Nonnative Map Turtle (Graptemys pseudogeographica) Occurring Syntopically with Two Endemic Graptemys in the Pearl River, Mississippi

Humans commonly move turtles and tortoises across geopolitical and geographic boundaries through food markets and the pet trade. One group commonly encountered in the pet trade is the genus Graptemys (map turtles and sawbacks). In the late 1980s, Graptemys pseudogeographica (false map turtle) was documented outside of its native range in the Pearl River near Jackson, Mississippi. Through replicated visual surveys in 2017 and 2018, we found that G. pseudogeographica persists in this location, but their densities were low (0.22/river km; 0.5% of all observations) compared with the 2 native Graptemys species. We evaluated the historical avenues for introduction via natural or human-mediated routes. Based on topographic profiles and historical hydrologic records, we strongly refute a prior hypothesis that G. pseudogeographica naturally colonized the Pearl from a neighboring drainage during the Easter Flood of 1979. Rather, we suggest that introduction via the release of unwanted pets is a more parsimonious conclusion. Because the lineage is shallowly diverged on an evolutionary scale, it seems possible that hybridization could occur between introduced G. pseudogeographica and Graptemys oculifera. Consequently, genetic introgression of the nonnative G. pseudogeographica genome is a possible threat to G. oculifera, a federally threatened species. This is a conservation concern to be further evaluated.