The invasion of Patagonia by Chinook salmon (Oncorhynchus tshawytscha): inferences from mitochondrial DNA patterns

Abstract

The Chinook salmon Oncorhynchus tshawytscha, which was introduced deliberately in Chile four decades ago for sport fishing and aquaculture, represents a rare example of a successful translocation of an anadromous Pacific salmon into the southern Hemisphere, offering a unique opportunity to examine the role of introduction history and genetic variability in invasion success. We used historical information and mitochondrial displacement loop sequences (D-loop) from seven colonized sites in Chile and Argentina and from native and naturalized Chinook salmon populations to determine population sources and to examine levels of genetic diversity associated with the invasion. The analysis revealed that the Chinook salmon invasion in Patagonia originated from multiple population sources from northwestern North America and New Zealand, and admixed in the invaded range generating genetically diverse populations. Genetic analyses further indicated that the colonization of new populations ahead of the invasion front appear to have occurred by noncontiguous dispersal. Dispersal patterns coincided with ocean circulation patterns dominated by the West Wind Drift and the Cape Horn Currents. We conclude that admixture following multiple introductions, as well as long-distance dispersal events may have facilitated the successful invasion and rapid dispersal of Chinook salmon into Patagonia.

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

“…We covered the entire distributional range of Chinook salmon among Pacific Ocean and Atlantic Ocean basins in South America by supplementing archived samples of seven populations (Riva‐Rossi et al., ) with contemporary collections of two populations. Archived samples were collected during 2005–2009 and included Estero Pichicolo (PIC), a hatchery population, and Pacific Ocean rivers Cobarde (COB), Vargas (VAR), Serrano (SER), and Prat (PRA).…”

“…Second, we simulated hybrid classes (F1, F2, and backcrosses) in HYBRIDLAB (Nielsen, Bach, & Kotlicki, ) from randomly sampling 100 genotypes from each of two selected geographic regions. We explored whether true hybrids could be reliably assigned to their parental genotypes using mixture analysis, because mtDNA evidence suggests that substantial hybridization may have occurred between founding lineages in South America (Riva‐Rossi et al., ).…”

“…Introductions of Pacific salmon into the Southern Hemisphere, especially New Zealand and South America, have provided unique research opportunities to investigate the relative roles of propagule pressure, preadaptations, phenotypic plasticity, and low ecosystem resistance in explaining invasions (Arismendi et al., ; Pascual et al., ; Quinn, Kinnison, & Unwin, ). Several genetics studies in South America have ascertained the origin of donor (native) salmonid populations (Ciancio, Riva‐Rossi, Pascual, Anderson, & Garza, ; Riva‐Rossi, Lessa, & Pascual, ; Riva‐Rossi et al., ). Other studies have shown significant gains in genetic diversity among non‐native populations that may be important for invasion success (Correa & Moran, ; Di Prinzio, Rossi, Ciancio, Garza, & Casaux, ; Narum et al., ).…”

“…Chinook salmon were also repeatedly introduced to South America via several government‐sponsored and private initiatives during most of the twentieth century, both in Chile and in Argentina, to develop recreational and commercial fisheries as well as net‐pen aquaculture (Basulto, ; Pascual & Ciancio, ). Several studies indicate that successful introductions of Chinook salmon to South America, with adults returning in large numbers, occurred following sea‐ranching experiments in the Lake (X Region) and Magallanes (XII Region) districts in Chile at the end of 1970s and beginning of 1980s (Correa & Gross, ; Niklitschek & Toledo, ; Riva‐Rossi et al., ; Soto, Arismendi, Di Prinzio, & Jara, ). Many other populations have formed beyond initial and well‐documented stocking sites, suggesting that Chinook salmon in South America comprise both artificial and natural populations (Table ).…”

“…Many other populations have formed beyond initial and well‐documented stocking sites, suggesting that Chinook salmon in South America comprise both artificial and natural populations (Table ). Past and recent genetics and genomics studies have identified multiple donor populations of Chinook salmon that likely interbred and now coexist among Pacific Ocean and Atlantic Ocean basins (Correa & Moran, ; Narum et al., ; Riva‐Rossi et al., ). Both individual assignment and genetic analysis of population mixtures (McKinney, Seeb, & Seeb, ) have greatly assisted tracking the geographic origin of donor Chinook salmon populations to various sites in South America (Ciancio et al., ; Correa & Moran, ; Di Prinzio et al., ).…”