Mitochondrial DNA Variation in Native and Introduced Populations of Smallmouth Bass, Micropterus dolomieu

The smallmouth bass (Micropterus dolomieu) is native to drainages of the central United States and southern Canada (Coble, 1975), where it is an ecologically important predator in rivers, lakes, and streams (Sowa and Rabeni, 1995). The species was introduced to eastern north America during the mid-19th century, most likely from the Ohio River drainage (Jordan, 1888; Jenkins and Burkhead, 1993), and is established widely in nontidal sections of Atlantic slope rivers and their tributaries from Nova Scotia to South Carolina (Coble, 1975; Hocutt et al., 1986). In many of these coastal river systems, smallmouth bass have become numerically dominant and support important recreational fisheries (Garman and Nielsen, 1992). Little is known about the timing or locations of smallmouth bass introductions to Atlantic slope drainages or whether different genetic sources were involved (ordan, 1888; Raney, 1950;Jenkins and Burkhead, 1994). Vagility in riverine smallmouth bass is limited (Coble, 1975), and dams may have provided a potential isolating mechanism for genetically distinct strains originally introduced at various locations within drainages. At least five mainstem dams were constructed on the James River, Virginia, prior to initial smallmouth bass introductions to the drainage (Raney, 1950). Biological studies of the James River system (Garman and Nielsen, 1992) documented intradrainage differences in several aspects of smallmouth bass life history; specifically, growth rates, longevity, and spawning patterns of the species differed substantially among adjacent river sections. Isely et al. (1987) reported that genetically distinct groups of largemouth bass (Micropterus salmoides) held under similar conditions showed different first-year growth rates, suggesting that observed phenotypic differences were genetically based. In contrast, growth differences within the genus Micropterus also have been attributed to environmental effects such