Data from: Sixty years of anthropogenic pressure: a spatio-temporal genetic analysis of brown trout populations subject to stocking and population declines

Analyses of historical samples can provide invaluable information on
changes to the genetic composition of natural populations resulting from
human activities. Here, we analyze 21 microsatellite loci in historical
(archived scales from 1927-1956) and contemporary samples of brown trout
(Salmo trutta) from six neighbouring rivers in Denmark, to compare the
genetic structure of wild populations before and after population declines
and stocking with non-local strains of hatchery trout. We show that all
populations have been strongly affected by stocking, with admixture
proportions ranging from 14 to 64%. Historical population genetic
structure was characterized by isolation-by-distance and by positive
correlations between historical effective population sizes and habitat
area within river systems. Contemporary population genetic structure still
showed isolation-by-distance, but also reflected differences among
populations in hatchery trout admixture proportions. Despite significant
changes to the genetic composition within populations over time, dispersal
rates among populations were roughly similar before and after stocking. We
also assessed whether population declines or introgression by hatchery
strain trout should be the most significant conservation concern in this
system. Based on theoretical considerations, we argue that population
declines have had limited negative effects for the persistence of adaptive
variation, but admixture with hatchery trout may have resulted in reduced
local adaptation. Collectively, our study demonstrates the usefulness of
analyzing historical samples for identifying the most important
consequences of human activities on the genetic structure of wild
populations.