Population structure of brown trout (Salmo trutta), a host of freshwater pearl mussel (Margaritifera margaritifera) in Lake Norsjø tributaries

Abstract

Brown trout (Salmo trutta) is one of a few suitable host species for endangered freshwater pearl mussel (Margaritifera margaritifera). Freshwater pearl mussel larvae (glochidia) are obligate parasites. Glochidia, must attach to the gills of a suitable host fish, which in our study area is brown trout only. Microsatellite markers have been proven to express levels of genetic variation. We used 13 DNA microsattelite markers to evaluate population structure of brown trout (Salmo trutta) in three tributaries of Lake Norsjø, Telemark County, Norway. Genetic differentiation between rivers was found. It was indicated by our results that the river populations are composed of smaller subpopulations with gene flow strongly influencing the genetic variation, and recommended to treat each rivers as one population. We compared genetic diversity and population structure of brown trout and freshwater pearl mussel. Convergence between genetic diversity was found, as less diversity was found in upstream parts of rivers. Because the freshwater pearl mussel showed high genetic variability, compared to previous studies, it may be possible that high gene flow in host populations is beneficial.