Maintenance of Genetic Diversity during Reintroduction: Assessment Among Potential Parents, Offspring, and Migrants at Two Spring Chinook Salmon Programs

Reintroduction programs provide salmonid populations access to historical habitat, however little is known about the demographic and evolutionary consequences of these actions. Here we evaluated if genetic diversity was maintained in two reintroduction programs, because maintenance of genetic variation is important for maximizing future adaptive potential. Using previously constructed genetic pedigrees and associated microsatellite genotypes, we examined whether genetic diversity was maintained between reintroduced cohorts and F₁ progeny (age-3 to age-5) that returned in subsequent years to dams on the South Fork McKenzie and South Santiam rivers, Oregon. In all comparisons, the average number of alleles observed at each locus decreased between potential parents and offspring; however observed heterozygosity did not differ. Results suggest that most alleles were lost as a result of genetic drift, likely mediated by the highly skewed fitness of reintroduced salmon/parents. However our results also indicated that migrants, defined here as individuals not produced above dams, restored some genetic variation that was lost between potential parents and offspring, and contributed genetic variants not previously observed in reintroduced salmon. Our results indicate that gene flow will be vital to the long term viability of these reintroduction programs.