The invasion of an Atlantic Ocean river basin in Patagonia by Chinook salmon: new insights from SNPs

Abstract

Chinook salmon spawning was first reported in the 1980s in the Caterina River tributary of the Santa Cruz River basin of Patagonia, which drains into the Atlantic Ocean. A naturalized population now persists and its source has been debated. Chinook salmon from California populations was directly released into the Santa Cruz River in the early twentieth century, but ocean ranching experiments on the Pacific coast of Patagonia (Chile) also released Chinook salmon of lower Columbia River origin (University of Washington hatchery stock) in the late twentieth century. We used genetic stock identification with single nucleotide polymorphisms to explore the origin of this Chinook salmon population. The genotypes of salmon that invaded the Santa Cruz River were compared with those derived from 69 known populations from the Northern Hemisphere. Chinook Salmon of the Santa Cruz River were found to be most similar to those from the lower Columbia River. This supports the hypothesis that the Santa Cruz River population was founded from the ocean ranching in southern Chile and the river was invaded by fish straying from Pacific coast basins. Moreover, we find that the life history of these naturalized fish, as inferred from scale analysis, was similar to that of the progenitor stock. We suggest that the successful invasion of the Caterina River in Patagonia by Chinook salmon was aided by pre-adaptations of some of the stocks used in the ocean ranching experiments to conditions in the new environment, rather than a post-colonization adaptation.

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

“…Second, a decrease in H E and LD N b among natural populations may have occurred due to subsequent founder effects, which appeared especially pronounced among Chinook salmon populations that colonized Atlantic Ocean rivers. These possibly experienced further genetic drift subsequent to their colonization from populations previously established in Pacific Ocean basins (Ciancio et al., ; Riva‐Rossi et al., ). Mitochondrial gene diversity supports a similar result: D‐loop haplotype diversity among non‐native Chinook salmon in South America was higher among Pacific Ocean basins close to points of introduction than in so‐called peripheral populations such as CAT (Riva‐Rossi et al., ).…”

“…However, habitat variation causes salmon to stray selectively, so proximity is not the only factor influencing dispersal (Pascual & Quinn, ; Westley, Dittman, Ward, & Quinn, ). Additionally, the influence of oceanographic currents flowing southward along the southeastern Pacific Ocean (Cape Horn Current) and east into the Atlantic Ocean (West Wind Drift) may provide a directional component to dispersal from the Pacific Ocean to the Atlantic Ocean resulting in long‐distance gene flow (Becker, Pascual, & Basso, ; Ciancio et al., ; Riva‐Rossi et al., ).…”

“…A fourth cluster comprised Chinook salmon from SAC and CAT, two natural Atlantic Ocean populations that showed strong differentiation ( θ = 0.069–0.231; Table ) from all Pacific Ocean basins. Results from two mitochondrial DNA studies (Becker et al., ; Riva‐Rossi et al., ) and another using biparental SNPs (Ciancio et al., ) failed to support successful stocking of Chinook salmon from California, United States, to Atlantic Ocean basins at the beginning of the twentieth century. On the contrary, those studies supported the origin of propagules from Pacific Ocean basins during more recent periods.…”

“…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., ).…”

“…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., ). However, we lack a clear understanding on how genetic diversity, dispersal, and genetic admixture are linked to artificial and natural dispersal pathways of this species from its distributional range in South America.…”