Ancestry and genetic structure of resident and anadromous rainbow trout (Oncorhynchus mykiss ) in Argentina

Abstract

Since the first introduction from North America more than a century ago, rainbowtrout (Oncorhynchus mykiss) have rapidly established self-sustaining populations inmajor river basins of Patagonia. Many generations later, only the freshwater residentlife history is expressed in the Chubut and Negro rivers of northern Argentinian Pata-gonia, whereas both the resident and anadromous life histories are found in the SantaCruz River of southern Argentina. Despite previous studies that have tried to identifythe sources of these introduced populations, uncertainty still exists. Here we com-bined data from many single-nucleotide polymorphisms and microsatellite loci inO. mykiss populations from Argentina and North America to evaluate putative sourcepopulations, gene flow between Argentinian river basins, and genetic diversity differ-ences between Argentinian and North American populations. We found that popula-tions from northern and southern Patagonia are highly differentiated and havelimited gene flow between them. Phylogeographic analysis also confirmed that theyhave separate origins, with the northern populations most closely related to thedomesticated rainbow trout strains that are raised worldwide and the Santa CruzRiver populations most closely related to North American populations from Californiaand Oregon that have an anadromous component. In addition, fish with different lifehistories in the Santa Cruz River were found to constitute a single interbreeding pop-ulation. No evidence was found of reduced genetic variation in introduced rainbowtrout, suggesting multiple contributing sources. In spite of these advances in under-standing, significant questions remain regarding the origins and evolution of theintroduced O. mykiss in Patagonia.