**4. Discussion**

(*P* = 0.08, *H*<sup>0</sup> = 0.007), New River (*P* = 0.34, *H*<sup>0</sup> = 0.064), and Holston River (*P* = 0.29, *H*<sup>0</sup> = 0.100) populations. Atlantic-slope populations exhibited lower mean percent polymorphic loci and heterozygosity values (*P* = 0.05, *H*<sup>0</sup> = 0.004) than Gulf of Mexico drainage populations (*P* = 0.33, *H*<sup>0</sup> = 0.068). Analysis of molecular variance showed that approximately 34% of the total genetic diversity resulted from variation within populations, 18% among populations within drainages, and 48% among drainages. Most of the total limiting variance was attributed to the *CK-A2*\* locus, meaning that most of the variance that we measured with allozyme markers was due to differentiation among northern and southern lineages of the species.

There was no apparent pattern regarding where populations characterized as southern, northern, or introgressed were located geographically within the New, Holston, Yadkin, and James drainages (**Figure 1**). Cluster analysis of unbiased genetic distances [38] among all populations showed that all populations of northern origin or with a high frequency of the *CK-A2*\*78 allele clustered together; these included populations from the James River drainage (Barbours Creek, Ewin Run, and Pickles Branch), the Holston drainage (Henshew Creek), the New River drainage (Pearis Thompson and Little Indian Creek), and Paint Bank Hatchery. The Roaring Fork population in the Holston drainage had a high frequency of the northern allele, but did not cluster closely with the other northern populations due to a high frequency of a rare allele at the *GPI-A*\* locus. Cluster analysis of unbiased genetic distances [38] among populations showed no geographic patterns of

**Yadkin River**

**Figure 1.** Genetic characterization at the *CK-A2*\* locus for 83 wild brook trout populations in southwest Virginia,

Northern

Genetic Characterization

**James River**

VA

**Roanoke River**

Southern Introgressed

genetic variation among the populations of putative southern Appalachian origin.

**New River**

including 56 populations characterized in this study and 27 populations characterized previously.

Scale (km) 0 10 20 30 40 50

WV

TN

**Holston River**

NC

VA

62 Biological Resources of Water
