Mixed evidence for reduced local adaptation in wild salmon resulting from interbreeding with escaped farmed salmon: complexities in hybrid fitness
Date
2008-08
Authors
Fraser, Dylan J.
Cook, Adam M.
Eddington, James D.
Bentzen, Paul
Hutchings, Jeffrey A.
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Abstract
Interbreeding between artificially-selected and wild organisms can have negative fitness
consequences for the latter. In the Northwest Atlantic, farmed Atlantic salmon recurrently escape
into the wild and enter rivers where small, declining populations of wild salmon breed. Most farmed
salmon in the region derive from an ancestral source population that occupies a nonacidified river
(pH 6.0-6.5). Yet many wild populations with which escaped farmed salmon might interbreed inhabit
acidified rivers (pH 4.6-5.2). Using common garden experimentation, and examining two early-life
history stages across two generations of interbreeding, we showed that wild salmon populations
inhabiting acidified rivers had higher survival at acidified pH than farmed salmon or F(1)
farmed-wild hybrids. In contrast, however, there was limited evidence for reduced performance in
backcrosses, and F(2) farmed-wild hybrids performed better or equally well to wild salmon. Wild
salmon also survived or grew better at nonacidified than acidified pH, and wild and farmed salmon
survived equally well at nonacidified pH. Thus, for acid tolerance and the stages examined, we found
some evidence both for and against the theory that repeated farmed-wild interbreeding may reduce
adaptive genetic variation in the wild and thereby negatively affect the persistence of depleted
wild populations.
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Citation
Fraser, Dylan J., Adam M. Cook, James D. Eddington, Paul Bentzen, et al. 2008. "Mixed evidence for reduced local adaptation in wild salmon resulting from interbreeding with
escaped farmed salmon: complexities in hybrid fitness." Evolutionary Applications 1(3): 501-512.