A Population Genetics Study of Southern Appalachian Brook Trout

Observations of anglers and naturalists, and the findings of molecular genetics, indicate that native Southern Appalachian brook trout populations comprise a distinct lineage of Salvelinus fontinalis. In this century, the stream mileage inhabited by the region\u27s only native salmonid has been reduced by 70-80%. Attempts to restore declining populations by stocking have eroded the genetic integrity of many remaining native populations through hybridization with hatchery strains. In this study I review the decline and current status of brook trout in the Southern Appalachians (Part I), document the genetic structure of populations in Great Smoky Mountains National Park (Part II), delineate the geographical range and genetic structure of the Southern Appalachian lineage (Part III), and initiate the investigation of morphometric variation among northern and Southern Appalachian lineage populations and their hybrids (Part IV). Brook trout populations did not recover with Southern Appalachian forests after the depredations of the early decades of this century. Currently, much of their former range is occupied by introduced salmonids, primarily rainbow trout. In Great Smoky Mountains National Park, as elsewhere, attempts to restore declining populations relied extensively on stocking with hatchery strains derived from northeastern populations. Stocking records indicate that only 12 streams in the Park were not stocked with hatchery fish. Eleven of these unstocked streams and an additional 40 streams that had been stocked, were sampled. These samples, representing the majority of known Park populations, plus two hatchery strains and one naturalized hatchery derived population from the Park, were analyzed for variation in 15 proteins encoded by 24 loci. The unstocked samples and the hatchery samples were fixed for different alleles at the CK­ A2* locus, and exhibited significant differences in allele frequency at an additional 9 of 10 polymorphic loci. Samples from 28 of the 40 stocked streams were fixed for the diagnostic Southern Appalachian CK-A2* allele, indicating surprisingly low levels of hatchery gene introgression. Samples from 48 brook trout populations in Maryland, Virginia, North Carolina, and South Carolina were analyzed for variation at the same loci as Park samples to assess regional genetic structure. Variation at the CK-A2* locus and other variable loci demonstrates the existence of two discrete lineages of evolutionary and probably taxonomic significance. The Southern Appalachian lineage is found in Ohio River and Atlantic drainage streams from the New River southward, and the northern lineage is found in drainages north of the New River. Genetic heterogeneity among Southern Appalachian lineage populations is greater than that among northern lineage populations in my sample and indicates that the Southern Appalachians are a center of brook trout genetic diversity. Morphometric variation among northern and Southern Appalachian brook trout samples was not as clear as variation observed at allozyme loci. Significant differences between northern, southern, and hybrid samples were most evident in the means of head region morphometries adjusted for standard length. Means significantly different between northern and southern samples were intermediate in the hybrid samples. Southern Appalachian and hybrid samples also showed significantly lower variance than northern populations in some head region morphometries. Discriminant analyses of seven truss grid and two standard morphometries from a subset of the samples analyzed for allozyme variation were unable to distinguish between individuals from northern, Southern Appalachian, and hybrid populations