Genetic variation in time and space: Microsatellite analysis of extinct and extant populations of Atlantic salmon

Information on genetic composition of past and present populations may be o btained by analyzing DNA from archival samples. A study is presented on the genetic population structure of extant and extinct local populations of At lantic salmon from 1913 to 1989 using dried scales as a source of DNA. Vari ation at six microsatellite loci was studied. Tests for differentiation amo ng populations and among time series within populations showed that populat ion structure was stable over time. This was also confirmed by a neighbor-j oining dendrogram which showed a clear clustering of samples from individua l rivers that covered a time span of up to 76 years. These results suggest that salmon populations evolve as semi-independent units connected by modes t amounts of gene flow. Additionally, a clear association between geographi c and genetic distance was found. This relationship has otherwise been diff icult to establish in several recent studies. The discrepancy may be due to impact of human activities on the genetic structure of present populations , whereas old samples represent populations in a more unaffected state. How ever, other explanations related to differences in the sampling of past and present populations may be equally valid.