Genetic differentiation in Coregonus albula (L.) (Salmonidae) populations in Finland

Enzyme gene variability has been studied by starch gel electrophoresis in 20 Finnish vendace (Coregonus albula) populations. Eighteen populations originate from fresh water and two from brackish water. Fourteen populations spawned in the time typical for the species, i.e. in the autumn, four in the winter and two in the spring. Genotype-environment interactions were studied with regard to several hydrological and spatial variables. Genetic polymorphism in vendace is relatively high for a fish. About half of the enzyme loci studied were polymorphic and the mean heterozygosity per locus per individual is 0.08. The degree of polymorphism is related to the metabolic function of enzymes. The average genetic distance between populations, based on five polymorphic loci, is 0.036 (ranging from 0.001 to 0.245) and 0.016 based on all loci studied. The genetic distances indicate that the winter- and spring-spawning populations are the most differentiated. They differ also very much from each other. This indicates that each one of them has arisen independently from populations spawning in autumn. The change in spawning time can be attributed to selection operating on zygotes and juveniles. This selection is due to adverse winter oxygen conditions associated with dystrophy and warm water. The genetic differentiation observed between populations may be due to natural selection or genetic drift or both.