Genetic Structure of Spotted Bass ('Micropterus Punctulatus') in the Red River Basin

Abstract

Mitochondrial DNA sequence variation and allele frequencies for fIve microsatellite DNA loci was used to assess the genetic structur of spotted bass populations in the upper Red, Ouachita, and Arkansas river basins, with emphasis on those in the Red River Basin. Results for 318 spotted bass from 14 localities provide no evidence that the present spotted bass populations in western reaches ofthe Red River Basin carry remnants of variation that originated in a pre-glacial Ouachita River. The population in East Cache Creek, which potentially supported native populations of the nominal subspecies M. p. wichitae, appears to have been introduced from farther east in the Red River Basin. The pattern of overall similarity for both mtDNA and microsatellite DNA indicates that spotted bass in the Ouachita River Basin are more similar to those in the Arkansas River Basin than to those in the Red River Basin, a result that conflicts with expectations based on a previous Pleistocene model for the biogeography of the fishes of the region. These results, together with a nested clade analysis of mtDNA variation, suggest that the present pattern of genetic variation in spotted bass of the region is a result of recent events, possibly post-Pleistocene dispersal into the region. The result for microsatellite DNA showed no evidence of hybridization with smallmouth bass as a factor in the present genetic structure of spotted bass. The corresponding results for mtDNA provided no added resolution to this question because mtDNA is not divergent between the two species in the study area.