Genetic monitoring suggests ongoing genetic change in wild salmon populations due to hybridization with aquaculture escapees
Itzia Coral San Román, Ian Fleming, Steven Duffy, Melissa K. Holborn, Nicole C. Smith, Amber Messmer, Danielle Davenport, Ian Bradbury
Abstract
Abstract Substantial domestication associated divergence of farmed from wild Atlantic salmon has raised concerns regarding the negative impacts of farm escapees on the genetic integrity and adaptability of wild salmon populations. Studies from across the North Atlantic have repeatedly demonstrated the presence of hybridization and introgression from escapees into wild salmon populations, however longer-term genetic monitoring has rarely been conducted. Here we use targeted SNP panels to evaluate the presence of hybridization and subsequent introgression of escaped farmed salmon into 18 southern Newfoundland rivers and reconstruct the number of escapees contributing to hybrids sampled over an 8-year period encompassing three reported escape events. Ongoing hybridization was observed throughout the entire time series, with F1 young-of-the-year individuals detected every year, as well as a notable increase in the proportion of backcross wild fish. Population estimates of domestic admixture were highest in smaller rivers reaching up to 78%, and the amount of aquaculture-associated European ancestry within individuals ranged as high as 39%. Spatial patterns of hybridization were closely associated with proxies of wild population size based on habitat area. Genetic analyses of relatedness indicated that at least one farm escapee parent was present each year, with the highest estimated numbers occurring after two escape events. This 8-year genetic time series, the longest monitoring period for farm escapee impacts in North America, offers valuable insight into the ongoing genetic impacts of escaped farmed salmon on wild populations.