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      Fitness of hatchery-reared salmonids in the wild

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          Abstract

          Accumulating data indicate that hatchery fish have lower fitness in natural environments than wild fish. This fitness decline can occur very quickly, sometimes following only one or two generations of captive rearing. In this review, we summarize existing data on the fitness of hatchery fish in the wild, and we investigate the conditions under which rapid fitness declines can occur. The summary of studies to date suggests: nonlocal hatchery stocks consistently reproduce very poorly in the wild; hatchery stocks that use wild, local fish for captive propagation generally perform better than nonlocal stocks, but often worse than wild fish. However, the data above are from a limited number of studies and species, and more studies are needed before one can generalize further. We used a simple quantitative genetic model to evaluate whether domestication selection is a sufficient explanation for some observed rapid fitness declines. We show that if selection acts on a single trait, such rapid effects can be explained only when selection is very strong, both in captivity and in the wild, and when the heritability of the trait under selection is high. If selection acts on multiple traits throughout the life cycle, rapid fitness declines are plausible.

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          Stability and flexibility of epigenetic gene regulation in mammalian development.

           Wolf Reik (2007)
          During development, cells start in a pluripotent state, from which they can differentiate into many cell types, and progressively develop a narrower potential. Their gene-expression programmes become more defined, restricted and, potentially, 'locked in'. Pluripotent stem cells express genes that encode a set of core transcription factors, while genes that are required later in development are repressed by histone marks, which confer short-term, and therefore flexible, epigenetic silencing. By contrast, the methylation of DNA confers long-term epigenetic silencing of particular sequences--transposons, imprinted genes and pluripotency-associated genes--in somatic cells. Long-term silencing can be reprogrammed by demethylation of DNA, and this process might involve DNA repair. It is not known whether any of the epigenetic marks has a primary role in determining cell and lineage commitment during development.
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            Natural selection and the heritability of fitness components.

            The hypothesis that traits closely associated with fitness will generally possess lower heritabilities than traits more loosely connected with fitness is tested using 1120 narrow sense heritability estimates for wild, outbred animal populations, collected from the published record. Our results indicate that life history traits generally possess lower heritabilities than morphological traits, and that the means, medians, and cumulative frequency distributions of behavioural and physiological traits are intermediate between life history and morphological traits. These findings are consistent with popular interpretations of Fisher's (1930, 1958) Fundamental Theorem of Natural Selection, and Falconer (1960, 1981), but also indicate that high heritabilities are maintained within natural populations even for traits believed to be under strong selection. It is also found that the heritability of morphological traits is significantly lower for ectotherms than it is for endotherms which may in part be a result of the strong correlation between life history and body size for many ectotherms.
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              Genetic effects of captive breeding cause a rapid, cumulative fitness decline in the wild.

              Captive breeding is used to supplement populations of many species that are declining in the wild. The suitability of and long-term species survival from such programs remain largely untested, however. We measured lifetime reproductive success of the first two generations of steelhead trout that were reared in captivity and bred in the wild after they were released. By reconstructing a three-generation pedigree with microsatellite markers, we show that genetic effects of domestication reduce subsequent reproductive capabilities by approximately 40% per captive-reared generation when fish are moved to natural environments. These results suggest that even a few generations of domestication may have negative effects on natural reproduction in the wild and that the repeated use of captive-reared parents to supplement wild populations should be carefully reconsidered.
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                Author and article information

                Journal
                Evol Appl
                Evol Appl
                eva
                Evolutionary Applications
                Blackwell Publishing Ltd (Oxford, UK )
                1752-4571
                1752-4571
                May 2008
                : 1
                : 2
                : 342-355
                Affiliations
                [1 ]Department of Zoology, Oregon State University Corvallis, OR, USA
                [2 ]Eawag, The Swiss Federal Institute of Aquatic Science and Technology Kastanienbaum, Switzerland
                [3 ]NOAA, Northwest Fisheries Science Center Manchester, WA, USA
                [4 ]NOAA, Northwest Fisheries Science Center Seattle, WA, USA
                Author notes
                Michael Blouin, Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, OR 97331, USA. Tel.: 541 737 2362; fax: 541 737 0501; e-mail: blouinm@ 123456science.oregonstate.edu
                Article
                10.1111/j.1752-4571.2008.00026.x
                3352433
                © 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd
                Categories
                Synthesis

                Evolutionary Biology

                selection, captive breeding, conservation genetics, adaptation

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