Genetic variation in Scandinavian brown trout (Salmo trutta L.): evidence of distinct sympatric populations

Abstract

Large differences in certain morphological traits between populations of brown trout (Salmo trutta L.) in the lakes of northern Sweden led us to initiate an electrophoretic examination in an effort to understand the genetic structure of these populations. A total of 549 brown trout from four lakes were examined at 10 electrophoretically detected loci. Genetic variation was found at only three loci, coding for lactate dehydrogenase (LDH), alpha‐glycerophosphate dehydrogenase (AGP), and creatine phosphokinase (CPK). A total absence of heterozygotes at the LDH‐1 locus in Lake Bunnersjöarna, coupled with significant correlations between LDH‐1 type and both CPK‐1 allele frequencies and body size, is interpreted as evidence of two genetically isolated populations of brown trout in this lake. This finding, in addition to large allele frequency differences between brown trout from different lakes, is evidence of a large amount of genetic differentiation in these populations within a small geographical area. The implications of these results are discussed from both an evolutionary and a fishery management perspective. Further studies are planned to determine if these two sympatric populations are representatives of two widespread sibling species or are a locally evolved phenomenon. We also intend to detail the biochemical genetic, behavioral, and ecological differences between the two distinct populations in Lake Bunnersjöarna. © 1976 Mendelian Society of Lund