Comparison of levels of variability among loci: Table 2 lists a number of single locus statistics. The mean numbers of alleles and mean heterozygosity levels ob- served at the 10 allozyme loci were three to four times lower than seen at the DNA level. No correlation was seen, however, between allele numbers and heterozy- gosity levels for either set of markers. For the RFLP loci, this reflects the fact that the majority of alleles detected were either private or rare and thus had little effect on heterozygosity. The greater mean heterozygosity ob- served at the nuclear DNA markers resulted from the absence of loci exhibiting low levels of polymorphism and not from any tendency for the RFLP loci to possess greater individual heterozygosities. Table 2 shows that seven protein loci exhibit levels of polymorphism below that of the least variable RFLP locus (GM727). Frequen- cieso f the most common allele at all 17 RFLPs are presented graphically in Figure 3. All loci were domi- nated by, at most, three common alleles whose com- bined frequency exceeded 0.940 in all populations.