Abstract
Translocation of organisms within or outside its native range carries the risk of modifying the community of the recipient ecosystems and induces gene flow between locally adapted populations or closely related species. In this study, we evaluated the genetic consequences of large‐scale translocation of cleaner wrasses that has become a common practice within the salmon aquaculture industry in northern Europe to combat sea lice infestation. A major concern with this practice is the potential for hybridization of escaped organisms with the local, recipient wrasse population, and thus potentially introduce exogenous alleles and breaking down coadapted gene complexes in local populations. We investigated the potential threat for such genetic introgressions in a large seminatural mesocosm basin. The experimental setting represented a simulated translocation of corkwing wrasse (Symphodus melops) that occurs on a large scale in the Norwegian salmon industry. Parentage assignment analysis of mesocosm's offspring revealed 30% (195 out of 651 offspring) interbreeding between the two populations, despite their being genetically (F ST = 0.094, p < 0.05) and phenotypically differentiated. Moreover, our results suggest that reproductive fitness of the translocated western population doubled that of the local southern population. Our results confirm that human translocations may overcome the impediments imposed by natural habitat discontinuities and urge for immediate action to manage the genetic resources of these small benthic wrasses.
Highlights
Organisms are frequently released into natural environments inten‐ tionally or inadvertently, such as via ship's ballast water or escapees from aquaculture facilities (Laikre, Schwartz, Waples, & Ryman, 2010; Swan, McPherson, Seddon, & Moehrenschlager, 2016)
We evaluated the genetic consequences of large‐scale translocation of cleaner wrasses that has be‐ come a common practice within the salmon aquaculture industry in northern Europe to combat sea lice infestation
The experimental set‐ ting represented a simulated translocation of corkwing wrasse (Symphodus melops) that occurs on a large scale in the Norwegian salmon industry
Summary
Organisms are frequently released into natural environments inten‐ tionally or inadvertently, such as via ship's ballast water or escapees from aquaculture facilities (Laikre, Schwartz, Waples, & Ryman, 2010; Swan, McPherson, Seddon, & Moehrenschlager, 2016). Putative deleterious genetic risks, associated with large‐scale releases and translocations, include the loss of genetic variation and adaptations as well as alterations in genetic profiles and population structure (Geller et al, 2010; Hӓnfling, 2007; Laikre et al, 2010). The large population sizes and extensive geographic areas commonly occupied by most marine fish make these studies very challenging (see refer‐ ences in Araki & Schmidt, 2010; Blanco Gonzalez, Aritaki, Knutsen, & Taniguchi, 2015). Apparent translocated individuals of goldsinny (Jansson et al, 2017) and corkwing wrasse (Faust, Halvorsen, Andersen, Knutsen, & André, 2018) have been found in the proximities of salmon farms in Norway, with indication of hybridization with locals for the latter species. We addressed several critical questions con‐ cerning the reproductive behavior of translocated fish: (a) Do local and translocated wild‐caught marine fish interbreed? (b) Do locally adapted populations present reproductive fitness advantage over translocated individuals? (c) Do specimens display any mating pref‐ erence regarding origin or phenotypic traits?
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