Cytonuclear Introgressive Swamping and Species Turnover of Bass After an Introduction

Abstract

Species-specific RFLP markers from mitochondrial DNA (mtDNA) were identified and employed in conjunction with previously reported data for nuclear allozyme markers to examine the genetic consequences of an artificial introduction of spotted bass (Micropterus punctulatus) into a north Georgia reservoir originally occupied by native smallmouth bass (M. dolomieul). The cytonuclear genetic data indicate that within 10–15 years following the unauthorized Introduction, a reversal in these species' abundances has occurred and that more than 99% of the population sample analyzed here consists of spotted bass or products of interspecific hybridization. This demographic shift, perhaps ecologically or environmentally mediated, has been accompanied by introgressive swamping; more than 95% of the remaining smallmouth bass nuclear and cytoplasmic alleles are present in individuals of hybrid ancestry. Dilocus cytonuclear disequilibria were significantly different from zero, with patterns indicative of an excess of homospecific genetic combinations (relative to expectations from single-locus allelic frequencies) and a disproportionate contribution of smallmouth bass mothers to the hybrid gene pool. Results document dramatic genetic and demographic changes following the human-mediated introduction of a nonnative species.