Among-locus variation in F-st: Fish, allozymes and the Lewontin-Krakauer test revisited

Variation among loci in the distribution of allele frequencies among subpop ulations is well known; how to tell when the Variation exceeds that expecte d when all loci are subject to uniform evolutionary processes is not well k nown. If locus-specific effects are important, the ability to detect those effects should vary with the level of gene flow. Populations with low gene flow should exhibit greater variation among loci in F-st than populations w ith high gene flow, because gene flow acts to homogenize allele frequencies among subpopulations. Here I use Lewontin and Krakauer's k statistic to de scribe the variance among allozyme loci in 102 published data sets from fis hes. As originally proposed, k much greater than 2 was considered evidence that the Variation in F-st among loci is greater than expected from neutral evolution. Although that interpretation is invalid, large differences in k in different populations suggest that locus-specific forces may be importa nt in shaping genetic diversity. In these data, k is not greater for popula tions with expected low levels of gene flow than for populations with expec ted high levels of gene flow. There is thus no evidence that locus-specific forces are of general importance in shaping the distribution of allele fre quencies at enzyme loci among populations of fishes.