Genetic signals of artificial and natural dispersal linked to colonization of South America by non-native Chinook salmon (Oncorhynchus tshawytscha)

GOMEZ-UCHIDA, DANIEL; CAÑAS-ROJAS, DIEGO; RIVA ROSSI, C; CIANCIO, J.E; PASCUAL, M.A.; ERNST, B.; AEDO, E.; MUSLEH, SELIM; VALENZUELA-AGUAYO, FRANCISCA; QUINN, T.P.; SEEB, JAMES; SEEB, LISA

Ecology and Evolution

John Wiley & Sons Ltd

Año: 2018

2045-7758

Invasion studies based on genetics data have provided unprecedented insights into evolutionary aspects of colonization among non-native populations. Yet, our understanding of how artificial (human-mediated) and natural dispersal pathways of non-native individuals influence genetic metrics, evolution of genetic structure, and admixture remains elusive. We capitalize on the widespread colonization of Chinook salmon Oncorhynchus tshawytscha, which has been mediated by both dispersal pathways in South America, to address these issues using data from a panel of 172 polymorphic SNPs. First, genetic diversity and the number of effective breeders (Nb) was higher among artificial than natural populations. Contemporary gene flow was common between adjacent artificial and natural as well as natural-alone populations and uncommon between far distant populations. Second, genetic structure revealed four distinct clusters throughout Chinook salmon distributional range with varying levels of genetic connectivity. Isolation-by-distance resulted from weak differentiation between adjacent artificial and natural as well as natural-alone populations combined with strong differentiation between far distant Atlantic populations experiencing strong genetic drift. Third, genetic mixture analyses revealed the presence of at least six donor geographic regions from North America, some of which likely hybridized as a result of multiple introductions. Relative propagule pressure or the proportion of Chinook salmon propagules introduced from various geographic regions according to government records significantly influenced genetic mixtures for two of three artificial populations. Our findings support a model of colonization in which high-diversity artificial populations became established, some of which following significant admixture resulting from propagule pressure, and low-diversity natural populations were subsequently founded from a reduced number of individuals (founder effect) via gene flow.