Testing the effects of genetic crossing distance on embryo survival within a metapopulation of brown trout (Salmo trutta)
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Predicting progeny performance from parental genetic divergence can potentially enhance the efficiency of supportive breeding programmes and facilitate risk assessment. Yet, experimental testing of the effects of breeding distance on offspring performance remains rare, especially in wild populations of vertebrates. Recent studies have demonstrated that embryos of salmonid fish are sensitive indicators of additive genetic variance for viability traits. We therefore used gametes of wild brown trout (Salmo trutta) from five genetically distinct populations of a river catchment in Switzerland, and used a full factorial design to produce over 2,000 embryos in 100 different crosses with varying genetic distances (F ST range 0.005–0.035). Customized egg capsules allowed recording the survival of individual embryos until hatching under natural field conditions. Our breeding design enabled us to evaluate the role of the environment, of genetic and non-genetic parental contributions, and of interactions between these factors, on embryo viability. We found that embryo survival was strongly affected by maternal environmental (i.e. non-genetic) effects and by the microenvironment, i.e. by the location within the gravel. However, embryo survival was not predicted by population divergence, parental allelic dissimilarity, or heterozygosity, neither in the field nor under laboratory conditions. Our findings suggest that the genetic effects of inter-population hybridization within a genetically differentiated meta-population can be minor in comparison to environmental effects.
KeywordsGenetic distance Inbreeding Maternal effects Outbreeding Optimal outcrossing distance Additive genetic variance Salmo trutta Salmonidae
We thank E. Baumgartner, K. Bettge, B. Bracher, A. Bréchon, E. Clark, M. Escher, S. Gostely, N. Grandjean, U. Gutmann, L. Kocjancic-Curty, C. Küng, L. Milano, L. Müller, W. Müller, S. Nusslé, A. Ross-Gillespie, M. Schmid, B. von Siebenthal, H. Walther, and A. Wilson for valuable discussion and/or assistance in the field and in the laboratory, C. Primmer and the reviewers for comments on the manuscript, and C. Küng (Fisheries Inspectorate Bern) and K. Brönnimann (Burgergemeinde Belp) for permissions. This work was supported by the Bern canton, the foundation Maison de la Rivière, the Swiss National Science Foundation, and a Marie Curie Intra-European Fellowship to RBS.
Conflict of interest
The authors declare that they have no competing interests.
This video (51 seconds) shows the burial of an egg capsule into the river bed, and the later retrieval using a metal detector. (M4V 9825 kb)
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