Hybridization and Replacement of Roanoke Bass (Ambloplites cavifrons) with Invasive Rock Bass (A. rupestris) in Virginia: A Genetic Assessment of the Scope of the Problem

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The Roanoke Bass (Ambloplites cavifrons) is a sport fish endemic to the Roanoke, Chowan, Tar, and Neuse drainages in Virginia and North Carolina. Virginia populations of this species have declined over time, presumably in part due to competition and hybridization with Rock Bass (A. rupestris), an invasive congener introduced from the Gulf slope throughout the early 20th century. Displacement and hybridization were reported as early as the 1950s, but the current status of this invasion and its impacts on A. cavifrons populations are unknown. Eleven nuclear DNA microsatellite markers were developed to discriminate between A. cavifrons, A. rupestris, and their hybrids, and in doing so to assess the current distribution of A. cavifrons in Virginia. The panel of markers provided a high degree of resolution among these groups, further allowing us to separate F1 hybrids from backcrossed individuals. Our results suggest a complex mosaic of invasion, displacement, and introgression patterns across the range of A. cavifrons in Virginia. In some populations all individuals appear to remain genetically A. cavifrons, whereas in other populations A. cavifrons has been partially or completely replaced by A. rupestris and/or hybrids. In the Pigg watershed, an ongoing invasion is apparent, with A. rupestris dispersing upstream and hybridizing with A. cavifrons, whereas in another watershed upstream invasion is prevented for now by a small dam. Of eight Virginia watersheds that historically contained A. cavifrons, only five now contain predominantly A. cavifrons, and three of these are susceptible to future invasion. This research helps to identify intact A. cavifrons populations that could be targeted for habitat restoration efforts, as well as vulnerable populations that could be targeted for programs seeking to prevent the spread of A. rupestris from adjacent waterways.


Southeastern Fishes Council Annual Meeting (SFC)


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