Effect of natural selection on the duplicated lysyl oxidase gene in Atlantic salmon.

We examined the polymorphism of the lysyl oxidase (LOX) locus, involved in the initiation of muscle collagen cross-linking, in three populations of Atlantic salmon with different life histories and growth rates and compared it with a closely related species (rainbow trout). Up to four alleles were observed per individual, probably as a consequence of the tetraploid origin of the salmonid genome. We found high polymorphism in the LOX locus (16 alleles expressed in total and several low frequency private alleles) in two natural Atlantic salmon populations and extremely reduced diversity in a farmed population (3 alleles) with low density of collagen crosslinks. We also assessed the relative role of selection in maintaining LOX genetic variability in Atlantic salmon. Results from several neutrality tests suggest that selection is playing a role in shaping diversity at the LOX locus. Positive selection was inferred by three different likelihood phylogeny-based methods and one selected site, identified by all three different methods (PAML, FEL and REL) was located within the "copper-talon" characteristic of LOX proteins. We suggest that the retention of four alleles in the salmon LOX locus could be related to its multiple functions.