The findings, which illuminate how programs of gene expression have evolved to control profoundly different developmental outcomes, are reported in the April 18th issue of Current Biology by Drs. Thomas Giger, Carlo Largiadèr, and Laurent Excoffier of the University of Bern, along with colleagues from France, Ireland, Denmark, and the UK.
Salmonid fish, which include trout and whitefish as well as salmon, show exceptional levels of life-history variation--that is, residential and migratory types often co-occur within a single population of young fish. Before reaching sexual maturity and leaving their natal stream, migratory individuals undergo dramatic morphological, physiological, and behavioral changes that prepare them for adulthood in open fresh and salty waters.
In their innovative work, which is based on studying the gene expression profiles of hundreds of genes at a time in different fish populations, the researchers studied gene expression in two species--strains of the brown trout, Salmo trutta, and a strain of the Atlantic salmon, Salmo salar. The researchers showed that many genes of genetically similar sedentary and migrant populations living in the same river were expressed at different levels. At the same time, two sedentary brown trout populations from Denmark and France, despite having diverged half a million years ago, showed very similar gene expression profiles. This remarkable similarity in gene expression between populations sharing the same life history--but being genetically very divergent and occupying different habitats--suggests that the genetic program of a given life history has been a highly selected attribute during the evolution of brown trout populations.
The findings also indicate that such striking differences in gene expression profiles are probably controlled by only a few major genes.
In addition, the authors showed that while there is a large diversity in gene expression levels between individuals from the same population, the different expression profiles associated with lifestyle fates were so distinct that by measuring the expression levels of relevant genes, it was possible to predict the future lifestyle of fish at the juvenile stage.
The researchers include Thomas Giger, Laurent Excoffier, Philip J. R. Day, Alexis Champigneulle, Michael M. Hansen, Richard Powell and Carlo R. Largiadèr of the University of Bern in Bern, Switzerland. This work was supported by the Swiss National Science Foundation grant 3100-067136.01 to C.R.L.
Giger et al.: "Correspondence: Life history shapes gene expression in salmonids." Publishing in Current Biology 16, R281-R282, April 18, 2006. www.current-biology.com.
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