MITOCHONDRIAL-DNA AND NUCLEAR MICROSATELLITE DIVERSITY IN HATCHERY AND WILD ONCORHYNCHUS-MYKISS FROM FRESH-WATER HABITATS IN SOUTHERN CALIFORNIA

We examined mitochondrial control-region haplotype diversity and allel ic frequency distributions for three polymorphic microsatellite loci i n 541 coastal Oncorhynchus mykiss collected from six habitats associat ed with different levels of human activity and ocean access in souther n California. Extensive urbanization, climatic unpredictability, and t he accelerated rate of decline in anadromous fish suggested a probable loss of genetic diversity in this area due to habitat fragmentation, geographic isolation, and population bottlenecks. Unexpectedly high le vels of genetic diversity were found in southern California population s of O. mykiss. Haplotype diversity (H-S) was highest in anadromous fi sh (H-S = 0.74) and lowest in the Whale Rock Hatchery trout (H-S = 0.3 2). The proportion of variation attributable to population differentia tion among habitat groups (G(ST)) was 10%. Haplotype frequencies showe d a close relationship between anadromous steelhead and resident rainb ow trout from closed habitats (D-ST = 0.03). Combined microsatellite a llelic diversity (at loci Omy77, Omy207, and Ssa289) was highest in ra inbow trout from closed habitats (88%), and lowest in Whale Rock Hatch ery fish (29%). Greatest microsatellite distance (delta mu = 17.1) was between anadromous steelhead and reservoir rainbow trout, and closest identity (delta mu = 1.8) was among rainbow trout from closed habitat s, hatchery rainbow trout, and reservoir rainbow trout. Analysis of ge netic distance measures for both molecular markers showed that conside rations of life history patterns and freshwater habitats that retain o cean access remain important factors in the preservation of the unique genetic diversity found in southern California coastal O. mykiss.