Abstract
To predict how climate change will influence populations it is necessary to understand the mechanisms, particularly microevolution and phenotypic plasticity, which allow populations to persist in novel environmental conditions. Although evidence for climate-induced phenotypic change in populations is widespread, evidence documenting that these phenotypic changes are due to microevolution is exceedingly rare. In this study we use 32 years of genetic data (17 complete generations) to determine whether there has been genetic change toward earlier migration timing in a population of pink salmon that shows phenotypic change; average migration time occurs nearly 2 weeks earlier than it did 40 years ago. Experimental genetic data support the hypothesis that there has been directional selection for earlier migration timing, resulting in a substantial decrease in the late migrating phenotype (from >30% to <10% of the total abundance). From 1983-2011 there was a significant decrease – over three fold – in the frequency of a genetic marker for late migration timing, but there were minimal changes in allele frequencies at other neutral loci. These results demonstrate there has been rapid microevolution for earlier migration timing in this population. Circadian rhythm genes, however, did not show any evidence for selective changes from 1993-2009.