Contrasting genetic metrics and patterns among naturalized rainbow trout (Oncorhynchus mykiss) in two Patagonian lakes differentially impacted by trout aquaculture

Abstract

Different pathways of propagation and dispersal of non‐native species into new environments may have contrasting demographic and genetic impacts on established populations. Repeated introductions of rainbow trout (Oncorhynchus mykiss) to Chile in South America, initially through stocking and later through aquaculture escapes, provide a unique setting to contrast these two pathways. Using a panel of single nucleotide polymorphisms, we found contrasting genetic metrics and patterns among naturalized trout in Lake Llanquihue, Chile's largest producer of salmonid smolts for nearly 50 years, and Lake Todos Los Santos (TLS), a reference lake where aquaculture has been prohibited by law. Trout from Lake Llanquihue showed higher genetic diversity, weaker genetic structure, and larger estimates for the effective number of breeders (N b) than trout from Lake TLS. Trout from Lake TLS were divergent from Lake Llanquihue and showed marked genetic structure and a significant isolation‐by‐distance pattern consistent with secondary contact between documented and undocumented stocking events in opposite shores of the lake. Multiple factors, including differences in propagule pressure, origin of donor populations, lake geomorphology, habitat quality or quantity, and life history, may help explain contrasting genetic metrics and patterns for trout between lakes. We contend that high propagule pressure from aquaculture may not only increase genetic diversity and N b via demographic effects and admixture, but also may impact the evolution of genetic structure and increase gene flow, consistent with findings from artificially propagated salmonid populations in their native and naturalized ranges.

Genetic Differentiation and Origin of Naturalized Rainbow Trout Populations From Southern Chile, Revealed by the mtDNA Control Region Marker

“…For example, Benavente et al (2015) provided evidence of the occurrence of this process, since a population of rainbow trout that inhabit a stream of Llanquihue Lake could have originated through the establishment of escaped farm broodstocks. Although specific experimental designs are required to address this question, some reports suggest that part of the genetic diversity currently found in naturalized populations from southern Chile has been shaped through the interbreeding of cultured strains with existing naturalized populations (Consuegra et al, 2011;Canales-Aguirre et al, 2018). Our result would also reflect this process, especially in sites where intensive trout farming activities related to smolt production have taken place in recent decades, as had occurred in Ranco Lake, Puyehue Lake and Llanquihue Lake (Arismendi et al, 2009).…”

“…The level of genetic structuring recorded in our study (F ST = 0.169) is higher than that reported in other studies of naturalized populations of rainbow trout distributed in southern Chile. Since in previous studies the genetic analysis was usually limited to one or few basins located within a more restricted geographic area (Gajardo et al, 1998;Consuegra et al, 2011;Canales-Aguirre et al, 2018), the high level of genetic structuring registered in our study may be related to the analysis of a broader geographic scale. In this regard, different factors, such as isolation by distance, among others, may play a significant role in increasing the differentiation among basins.…”

“…In Chile, there is little information on the origin or the lineages that compose the rainbow trout populations spread in natural environments and data on their evolutionary relationships with different varieties of North America. Genetic information available is limited to allozyme, microsatellite and single nucleotide polymorphisms (SNPs) variabilities in naturalized populations distributed in the south and north of the country (Gajardo et al, 1998;Consuegra et al, 2011;Benavente et al, 2015;Cárcamo et al, 2015;Canales-Aguirre et al, 2018). These studies helped to elucidate the diversity and structuring of rainbow trout inhabiting Chile, showing levels of genetic diversity similar to trout in its native distribution range (Gajardo et al, 1998;Consuegra et al, 2011).…”

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

“…Canales‐Aguirre et al. () found that estimates of LD N b were higher for non‐native rainbow trout populating a Patagonian lake with intensive trout aquaculture than for a lake where trout aquaculture has been prohibited by law. This highlights a possible role of continuous trout escapes and artificial dispersal on enlarging N b .…”

Chilean Salmon Sushi: Genetics Reveals Product Mislabeling and a Lack of Reliable Information at the Point of Sale

“…Although the bulk of Chile's salmonid production is exported, these three cultured species can also be sold nationally following statutory requirements [9]. In addition to aquaculture fish, Chile also supports widespread and abundant populations of naturalized salmonid fishes, where the entire life cycle is completed as free-living individuals [10] including rainbow trout, Chinook salmon (Oncorhynchus tshawytscha), and brown trout (Salmo trutta) [11][12][13][14]. There is evidence that such naturalized populations could make significant contributions to commercial services supporting human consumption (e.g., Chinook salmon), but the scale or geographical distribution of services for these species provide is unclear.…”