Ecological genetics of Norwegian Daphnia. I: Genetic differentiation between pigmented and unpigmented alpine pond populations

The genetic composition of seven Daphnia populations was studied by starch gel electrophoresis: one lowland lake population and six populations inhabiting mountain ponds. Four alpine populations consisted of darkly pigmented animals, two alpine ponds and the lake were populated by non-pigmented Daphnia. The population of each pond contained the same genotype; only two ponds contained the same dominating genotype. The genetic distance between pigmented and transparent Daphnia was of a magnitude commonly found in comparisons between different species, whereas genetic distances found within the groups of pigmented or non-pigmented Daphnia were of a magnitude consistent with the assumption of local populations of one species. This dichotomy suggests that melanin pigmentation did not evolve independently in several lineages, but was acquired by a common ancestor of all pigmented Daphnia studied. The genetic variability was much higher in the lake population than in any of the pond populations.