Decline of Bartram's Bass Due to Introgressive Hybridization With Invasive Alabama Spotted Bass

Invasives can promote extirpation or extinction of native species through a myriad of biological mechanisms. Introgressive hybridization, for example, can be just as detrimental as predation and competition especially for species with limited reproductive barriers such as fishes. Yet hybridization is often overlooked as an issue due to the inability to quantify without employing molecular genetic techniques. In this study we sampled individuals on two occasions, (2004, n=623; and 2010, n=653) from four reservoirs of the Savannah River drainage system (South Carolina) in an attempt to quantify hybridization and introgression between introduced species (Alabama Spotted Bass, Micropterus punctulatus henshalli; Smallmouth Bass, M. dolomieu) and endemics (Bartram’s Bass, M. sp. cf. coosae; Largemouth Bass, M. salmoides) over both temporal and spatial scales. Results are of special concern for Bartram’s Bass, a recently recognized rare lineage of Redeye Bass endemic only to the Savannah River. Three bi-allelic nuclear (nDNA) loci and one mitochondrial (mtDNA) locus were utilized for this study. Our results indicate overwhelming introgression between Alabama Spotted and Bartram’s Bass with strong selection for Alabama Spotted Bass genotypes within reservoirs. However, refugial areas in the tributaries may allow Bartram’s Bass to remain within the system and provides a source for management.