Anthropogenic effects on genetic diversity and life history strategies of Oncorhynchus mykiss

Variable life history characteristics in Oncorhynchus mykiss may have provided the diversity necessary to allow this species to persist and adapt to human disturbances. In addition to resident, estuarine, and anadromous ecotypes, there is considerable life history variation within each of these life history types. Resident rainbow trout spend their entire life in freshwater and disperse to nearby lakes and streams, but may interbreed with sympatric anadromous steelhead. Steelhead have one of the most diverse anadromous life histories of species of Pacific salmon. This includes duration of freshwater rearing as juveniles (typically one to three years) and number of spawning occurrences (iteroparous versus semelparous). Additionally, adult steelhead are classified as stream-maturing if they over-winter in freshwater prior to spawning (summer run), or ocean-maturing if they migrate from the ocean to native streams shortly before spawning (winter run). This dissertation addressed the effects of human disturbance on the interaction of these life history types of O. mykiss.; Results from case studies and broad analyses of O. mykiss populations from multiple sub-basins provided evidence that patterns of genetic diversity are related to characteristics of life history. Resident and anadromous ecotypes of the same sub-basin experience relatively high gene flow unless separated by barriers (i.e., waterfalls or dams), leading to higher differentiation among sub-basins than among ecotypes within sub-basins. Gene flow is high among summer (stream-maturing) and winter (ocean-maturing) run steelhead in the same sub-basin since spawning time is similar, but later migrating B-run summer steelhead appear to have significant differences in allele frequencies from A-run steelhead. Repeat spawning is also less common in B-run than A-run steelhead, presumably due to the evolution of semelparity related to larger body size of B-run fish.; Anthropogenic disturbances have negatively impacted the distribution of life history diversity in the Columbia River basin. The combination of habitat destruction/exclusion and planting of non-native hatchery stocks has lead to more homogenous distribution of genetic variation, rather than locally distinct populations. Due to widespread human disturbances to river ecosystems, both short- and long-term persistence of some populations and life histories of O. mykiss are questionable.