MITOCHONDRIAL AND NUCLEAR-DNA SEQUENCE VARIABILITY AMONG POPULATIONS OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Mitochondrial and nuclear DNA variability was examined to assess popul ation genetic structure and phylogeographic relationships in rainbow t rout. Single-strand conformation polymorphisms and restriction site di fferences within 1055 bp of the mitochondrial D-loop region and 1566 b p of nuclear DNA in six single-copy nuclear DNA regions identified 31 mitochondrial genotypes and 50 nuclear alleles. Gene trees were constr ucted by sequencing each variant allele or mitochondrial genotype iden tified. Examination of 30 populations in 10 native rainbow trout group s using an analysis of molecular variance (AMOVA) indicated that 65% o f mitochondrial variability and 35% of nuclear variability was explain ed by differences among the 10 groups. Phylogenetic patterns evident i n mitochondrial and nuclear DNA were not always concordant. Difference s in the evolutionary patterns detected by mitochondrial and nuclear D NA may reflect the differential impact of past introgression events on variability in the two genomes.