UC Santa Cruz

Perhaps one of the world's most important groups of fish are the species within the Pacific trout complex, due to their harvest in fisheries and use in aquaculture. This dissertation consists of an in-depth evaluation of this group at different scales, from the assessment of biological traits throughout the reconstruction of pedigrees in two populations to a phylogeographic examination of multiple largely undescribed species. Here, a combination of novel molecular techniques allowed me to address critical ecological questions for the management and conservation of this group.

In chapter one, I describe the discovery, characterization and development of single nucleotide polymorphisms for O. mykiss for the study of ecological interactions, phylogeography, and conservation status. These tools have great power for population genetic analysis, and for individual identification and pedigree reconstruction. The last allows the tracking of families, and an unprecedented level of evaluation of natural and hatchery populations.

Chapter two expands the scope of these molecular tools to provide a powerful means of understanding of biological traits for steelhead hatchery programs in the Russian River, California. Reconstruction of cohort age distributions revealed a strong component of fish that spawn at age two, in contrast to program goals and distinct from naturally spawning steelhead. Correlations between family members in the day of spawning revealed a strongly heritable component to this life history trait and demonstrated the potential for selection to alter life history traits. These results demonstrate the promise of SNP-based pedigree reconstruction for providing biological inference in high-fecundity organisms.

Chapter three describes how the molecular tools developed were applied to population genetics of trout inhabiting northwestern Mexico, to elucidate biodiversity, and evolutionary history, and measure introgression from hatchery rainbow trout. Here, I confirmed the vast genetic diversity present in northwestern Mexican trout and provided evidence that trout inhabiting the Sierra Madre Occidental correspond to independent lineages separated from O. mykiss. Introgression from non-native trout was detected, but the genetic integrity of native trout is still maintained. All the information presented in this document will help to guide effective conservation strategies for this globally important group of fishes.