Genetics data have provided unprecedented insights into evolutionary aspects of colonization by 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 in South America, mediated by both dispersal pathways, to address these issues using data from a panel of polymorphic SNPs. First, genetic diversity and the number of effective breeders (N b) were higher among artificial than natural populations. Contemporary gene flow was common between adjacent artificial and natural and adjacent natural populations, but uncommon between geographically distant populations. Second, genetic structure revealed four distinct clusters throughout the Chinook salmon distributional range with varying levels of genetic connectivity. Isolation by distance resulted from weak differentiation between adjacent artificial and natural and between natural populations, with strong differentiation between distant Pacific Ocean and Atlantic Ocean populations, which experienced 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 established first; some of these populations exhibited significant admixture resulting from propagule pressure. Low‐diversity natural populations were likely subsequently founded from a reduced number of individuals.

The Neotropical region hosts 4225 freshwater fish species, ranking first among the world's most diverse regions for freshwater fishes. Our NEOTROPICAL FRESHWATER FISHES data set is the first to produce a large‐scale Neotropical freshwater fish inventory, covering the entire Neotropical region from Mexico and the Caribbean in the north to the southern limits in Argentina, Paraguay, Chile, and Uruguay. We compiled 185,787 distribution records, with unique georeferenced coordinates, for the 4225 species, represented by occurrence and abundance data. The number of species for the most numerous orders are as follows: Characiformes (1289), Siluriformes (1384), Cichliformes (354), Cyprinodontiformes (245), and Gymnotiformes (135). The most recorded species was the characid Astyanax fasciatus (4696 records). We registered 116,802 distribution records for native species, compared to 1802 distribution records for nonnative species. The main aim of the NEOTROPICAL FRESHWATER FISHES data set was to make these occurrence and abundance data accessible for international researchers to develop ecological and macroecological studies, from local to regional scales, with focal fish species, families, or orders. We anticipate that the NEOTROPICAL FRESHWATER FISHES data set will be valuable for studies on a wide range of ecological processes, such as trophic cascades, fishery pressure, the effects of habitat loss and fragmentation, and the impacts of species invasion and climate change. There are no copyright restrictions on the data, and please cite this data paper when using the data in publications.

Limited stocking efforts to introduce Atlantic salmon Salmo salar into Chilean rivers and streams were unsuccessful during the 20th century. Following the arrival of the aquaculture industry during the 1980s, escaped Atlantic salmon have presented an ecological risk to native taxa through predation, competition, and transmission of pathogens or parasites. However, whether commercial aquaculture strains represent the likely source of free-living Atlantic salmon in marine and freshwater environments is unclear. We used 272 single nucleotide polymorphisms to characterize free-living Atlantic salmon (n = 80) captured from 12 marine and freshwater locations in southern Chile. These were compared with 8 reference collections, 6 known commercial strains, and 2 wild populations of Atlantic salmon. We evaluated genetic structure among free-living Atlantic salmon and assessed individual ancestry and origin by assigning mixture samples to reference collections. We found evidence for genetic structure (number of clusters, K = 3) among free-living salmon unexplained by geography, environment, or life stage, but consistent with the number of clusters among commercial aquaculture strains. Most free-living Atlantic salmon had a close ancestry with farmed Norwegian strains, the most widely used by the industry, pointing to recent aquaculture escapes as their origin. Yet recent establishment of self-sustaining populations weakly differentiated from aquaculture broodstock cannot be ruled out. We propose increasing monitoring efforts of free-living Atlantic salmon in remote sites as well as in watersheds located in densely stocked aquaculture areas.