The effects of Medieval dams on genetic divergence and demographic history in brown trout populations

Abstract

BackgroundHabitat fragmentation has accelerated within the last century, but may have been ongoing over longer time scales. We analyzed the timing and genetic consequences of fragmentation in two isolated lake-dwelling brown trout populations. They are from the same river system (the Gudenå River, Denmark) and have been isolated from downstream anadromous trout by dams established ca. 600–800 years ago. For reference, we included ten other anadromous populations and two hatchery strains. Based on analysis of 44 microsatellite loci we investigated if the lake populations have been naturally genetically differentiated from anadromous trout for thousands of years, or have diverged recently due to the establishment of dams.ResultsDivergence time estimates were based on 1) Approximate Bayesian Computation and 2) a coalescent-based isolation-with-gene-flow model. Both methods suggested divergence times ca. 600–800 years bp, providing strong evidence for establishment of dams in the Medieval as the factor causing divergence. Bayesian cluster analysis showed influence of stocked trout in several reference populations, but not in the focal lake and anadromous populations. Estimates of effective population size using a linkage disequilibrium method ranged from 244 to > 1,000 in all but one anadromous population, but were lower (153 and 252) in the lake populations.ConclusionsWe show that genetic divergence of lake-dwelling trout in two Danish lakes reflects establishment of water mills and impassable dams ca. 600–800 years ago rather than a natural genetic population structure. Although effective population sizes of the two lake populations are not critically low they may ultimately limit response to selection and thereby future adaptation. Our results demonstrate that populations may have been affected by anthropogenic disturbance over longer time scales than normally assumed.

Human mining activity across the ages determines the genetic structure of modern brown trout (Salmo trutta L.) populations

“…Thus, the impact of this chemical barrier appears to restrict fish movement to the same extent as physical barriers observed in some other systems (Hansen et al. ).…”

Echoes of a distant time: effects of historical processes on contemporary genetic patterns in Galaxias platei in Patagonia

“…Although our estimates in lakes with low contemporary connectivity were low, they were not as critically low as expected for populations experiencing high drift (see also Hansen et al . ). This is true in particular for the Lake Mellizas, an isolated lake occupying a small area with a long history of physical isolation.…”

“…; Hansen et al . ). However, while consideration of both temporal scales has increased over the last decade (Paun et al .…”

Population Genetic Structure and Genetic Diversity in Twisted-Jaw Fish,Belodontichthys truncatusKottelat & Ng, 1999 (Siluriformes: Siluridae), from Mekong Basin

“…The population genetic structure analysis based on the [26][27][28]. However, given that this dam is only 23 years old, it is unlikely to have had an impact on the genetic structure.…”