NEAFWA 2018

AUTHORS: Mary Gorton Janecka, Charles Criscione - Department of Biology, Texas A&M University; Jan E. Janecka, Department of Biological Sciences, Duquesne University

ABSTRACT. The construction of dams is one of the most pervasive and dramatic contemporary habitat modifications of the 20th and 21st centuries. Impoundments alter river and stream habitats directly by changing flow regime and increasing sedimentation. Dams are among the leading factors contributing to population reductions, isolation for freshwater organisms, and loss of biodiversity. The Concho watersnake (Nerodia paucimaculata) is a natricine endemic to central Texas. It was federally listed as a threatened species due to its small range, specific habitat requirements, and potential threats of habitat modification, specifically the construction of a major reservoir in 1990. The Concho watersnake was delisted in 2013 after surveys suggested it was able to persist in the reservoir. We conducted population genetic surveys of this species as part of the federally required post-delisting monitoring plan throughout the historic range on the Colorado and Concho Rivers. We developed eighteen species-specific microsatellites to assess effective population size and connectivity of 110 individuals captured from the upper Colorado River (UCR), within the reservoir (O.H. Ivie), and lower Colorado River (LCR)below the reservoir along the Colorado River. Despite extensive sampling, no Concho watersnakes were encountered or captured in the Concho River. Overall, the Concho water snake exhibited low genetic diversity (An: LCR = 4.615, O.H. Ivie = 3.385, and UCR = 3.23), (Hs : LCR = 0.516, O.H. Ivie = 0.479, and UCR = 0.504). Multiple structure analyses and Fst estimates support three genetic clusters corresponding to populations located above, below and within the dam. The O.H. Ivie Reservoir population exhibited the highest divergence, likely due to a founder effect. Our study suggests that low connectivity, coupled with prolonged drought conditions, may put the Concho watersnake at risk from bottlenecks and inbreeding, further promoting genetic drift. These effects could be ameliorated with a translocation program.