Genetic and morphometric differentiation among sympatric spawning stocks of whitefish (Coregonus lavaretus L.) in Lake Femund, Norway

Lake Femund, Norway, contains several sympatric ecotypes of whitefish, Coregonus lavaretus L. Deepwater whitefish, river whitefish, and shallow water whitefish can be easily distinguished by spawning habitat and gillraker number. Variation in morphological and ecological characters and allozyme loci from 11 different spawning sites was analysed to compare the ecological polymorphism with possible genetic sub-structuring of whitefish in the lake. Of the individual morphological and ecological characters, gillraker number best separated the spawning populations, followed by body length. In a hierarchical cluster analysis based on gillraker number, body length and age of fish, the four deepwater sites grouped together as well as the three samples from, or closely related to, inlet rivers. The shallow water sites, however, were more dispersed. In the allozyme analysis, nine of the 38 enzyme loci were polymorphic at the 0.95 level. The amount of genetic variation was quite similar among localities with Hexp = 0.046 - 0.066. Allele frequencies differed significantly among localities at all polymorphic loci indicating distinct reproductive isolation between spawning sites. A consensus tree based on genetic distances grouped samples according to spawning depth and trophic morphology rather than regional proximity. All deepwater spawners grouped together with rather high support while geographically adjacent samples differing by their morphology or behaviour were dispersed. The patterns of differentiation based on allozyme variation and morphology are not fully concordant, but still the association between genetic differentiation and morphological and life history variables was highly significant. Thus, the morphological differences are not due to phenotypic plasticity within single spawning populations as is commonly seen in many other fish species. The possible evolutionary origins of reproductively isolated whitefish forms are discussed. The relatively close association between differences in gillraker counts and genetic difference indicates that the present management of Femund whitefish stocks based on gillraker counts is sensible.