SEQUENCE DIVERGENCE IN THE MTDNA CONTROL REGION OF AMPHIDROMOUS AND LANDLOCKED FORMS OF AYU

We investigated mitochondrial DNA divergence for amphidromous and land locked forms of ayu Plecoglossus altivelis to describe their genetic s tatus and search for genetic markers discriminating the two forms. The first half of the control region was sequenced for 60 fish, 15 indivi duals from each of 2 amphidromous and 2 landlocked populations. These sequences were found to be highly variable, suggesting their utility f or the analysis of intra-specific divergence. The landlocked form was genetically more homogeneous than the amphidromous form in terms of th e number of polymorphic sites and the magnitude of nucleotide diversit y. Intra-form net nucleotide substitutions were 0.024% in the landlock ed and -0.062% in the amphidromous, showing that intra-form genetic di fferentiations were small. In contrast, inter-form net nucleotide subs titutions were considerably higher, 0.241-0.527%, indicating some gene tic heterogeneity in the mitochondrial genome between the two forms. N early 80% of fish were distinguishable as amphidromous or landlocked b y the nucleotide substitutions at hyper-variable sites.