Rangewide genetic structure in paddlefish inferred from DNA microsatellite loci

We surveyed paddlefish Polyodon spathula from 12 geographic locations encompassing the species' entire range at five polymorphic DNA microsatellite loci. Nearly all pairwise estimates of genetic heterogeneity among geographic samples were significant, as was the overall test of genetic heterogeneity. A test for isolation by distance was not significant. A neighbor-joining phenogram did not reveal any obvious phylogeographic patterns, other than a high degree of distinctiveness of the samples from the Tombigbee River and Grand Lake of the Ozarks and, to a lesser extent, the Mermentau River. The distinctiveness of the Mermentau and especially the Tombigbee River populations is not surprising because they are in different drainages. The distinctiveness of the Grand Lake population is accompanied by reduced heterozygosity, perhaps due to low effective population size or past stocking practices. We interpret the distribution of genetic variation in paddlefish as one of historically high levels of gene flow among populations that have more recently become isolated by habitat alteration (e.g., dams). Although we do not advocate large-scale movement of paddlefish, especially among historically isolated drainages, stocking practices that facilitate gene flow around recently erected barriers might be advisable. We also recommend additional analyses using microsatellites as a means of monitoring the genetic variation in paddlefish and the use of mitochondrial DNA to further investigate the historical isolation among drainages.