Chutes and Ladders: Drainage Exchange of Map Turtles (Genus Graptemys) Across the Tennessee-Tombigbee Waterway in Northeastern Mississippi

Abstract

The movement of nonindigenous aquatic species into new river systems has the potential to negatively impact native species and/or their environments. The construction of the Tennessee-Tombigbee Waterway (TTW) in the 1970s and 1980s directly linked 2 evolutionarily distinct aquatic communities, and faunal exchange across the TTW has been documented in both fishes and freshwater mussels. However, to date there have been no recognized exchanges of the turtle fauna between the Tennessee and Tombigbee river systems. Herein we document the exchange of Ouachita map turtles (Graptemys ouachitensis), a native of the Tennessee River system, and Alabama map turtles (Graptemys pulchra), a native of the Tombigbee River system, each occurring outside its native ranges in the opposite river system likely via dispersal in the TTW. For G. ouachitensis, we observed a range displacement of ∼ 55 river kilometers (rkm) south from the nearest specimen records in the Tennessee River system into upper Bay Springs Lake of the Tombigbee River drainage. Graptemys pulchra had a range displacement northward of ∼ 137 rkm from the nearest specimen record in the Tombigbee River system to Pickwick Lake of the Tennessee River drainage. For the latter, it seems most parsimonious that G. pulchra historically occurred farther north than the specimen record suggests. Otherwise, individuals would have had to execute movements through and/or around 4 locks and dams, which seems less probable. We recommend that additional monitoring of nonnative turtles should be conducted to document existing range and potential range expansions (inclusive of Graptemys nigrinoda, blackknobbed sawback) while studies to assess genetic introgression among these closely related species are warranted.