Consequences of farmed-wild hybridization across divergent wild populations and multiple traits in salmon
Date
2010-06
Authors
Fraser, Dylan J.
Houde, Aimee Lee S.
Debes, Paul V.
O'Reilly, Patrick
Eddington, James D.
Hutchings, Jeffrey Alexander
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Abstract
Theory predicts that hybrid fitness should decrease as population divergence increases. This
suggests that the effects of human-induced hybridization might be adequately predicted from the
known divergence among parental populations. We tested this prediction by quantifying trait
differentiation between multigenerational crosses of farmed Atlantic salmon (Salmo salar) and
divergent wild populations from the Northwest Atlantic; the former escape repeatedly into the wild,
while the latter are severely depleted. Under common environmental conditions and at the
spatiotemporal scale considered (340 km, 12 000 years of divergence), substantial cross
differentiation had a largely additive genetic basis at behavioral, life history, and morphological
traits. Wild backcrossing did not completely restore hybrid trait distributions to presumably more
optimal wild states. Consistent with theory, the degree to which hybrids deviated in absolute terms
from their parental populations increased with increasing parental divergence (i.e., the collective
environmental and life history differentiation, genetic divergence, and geographic distance between
parents). Nevertheless, while these differences were predictable, their implications for risk
assessment were not: wild populations that were equally divergent from farmed salmon in the total
amount of divergence differed in the specific traits at which this divergence occurred. Combined
with ecological data on the rate of farmed escapes and wild population trends, we thus suggest that
the greatest utility of hybridization data for risk assessment may be through their incorporation
into demographic modeling of the short- and long-term consequences to wild population persistence.
In this regard, our work demonstrates that detailed hybridization data are essential to account for
life-stage-specific changes in phenotype or fitness within divergent but interrelated groups of wild
populations. The approach employed here will be relevant to risk assessments in a range of wild
species where hybridization with domesticated relatives is a concern, especially where the
conservation status of the wild species may preclude direct fitness comparisons in the wild.
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Citation
Fraser, Dylan J., Aimee Lee S. Houde, Paul V. Debes, Patrick O'Reilly, et al. 2010. "Consequences of farmed-wild hybridization across divergent wild populations and multiple traits
in salmon." Ecological Applications 20(4): 935-953.