Effects of natural selection on patterns of DNA sequence variation at the transferrin, somatolactin, and p53 genes within and among chinook salmon (Oncorhynchus tshawytscha) populations

This paper describes DNA sequence variation within and among four populatio ns of chinook salmon (Oncorhynchus tshawytscha) at the transferrin, somatol actin and p53 genes. Patterns of variation among salmon species at the tran sferrin gene have been hypothesized to be shaped by positive natural select ion for new alleles because the rate of nonsynonymous substitution is signi ficantly greater than the rate of synonymous substitution. The twin goals o f this study were to determine if the history of selection among salmon spe cies at the transferrin gene is also reflected in patterns of intraspecific variation in chinook salmon, and to look for evidence of local adaptation at the transferrin gene by comparing patterns of nonsynonymous and synonymo us variation among chinook salmon populations. The analyses presented here show that unlike patterns of variation between species, there is no evidenc e of greater differentiation among chinook salmon populations at nonsynonym ous compared to synonymous sites. There is also no evidence of a reduction of within-species variation due to the hitchhiking effect at the transferri n gene, although in some populations nonsynonymous and synonymous derived m utations are both at higher frequencies than expected under a simple neutra l model. Population size weighted selection coefficients (4Ns) that are con sistent-with both the inter and intraspecific data range from similar to 10 to similar to 235, and imply that between 1 and 40% of new nonsynonymous m utations at the transferrin gene have been beneficial.