ECOLOGICAL GENETICS OF NORWEGIAN DAPHNIA .2. DISTRIBUTION OF DAPHNIA-LONGISPINA GENOTYPES IN RELATION TO SHORT-WAVE-RADIATION AND WATER COLOR

In the mountain range of South Norway, transparent and melanic members of the Daphnia longispina complex occur. Melanic populations inhabit clearwater lakes and ponds, while transparent populations are found in ponds with slightly humic water. Mixed populations have not been detected. The distribution patterns of the two morphs are related to ambient levels of short-wave radiation, and the light absorptive properties of the inhabited waters. The pigment present is probably melanin, which is deposited in the dorsally directed parts of the carapace, head shield and antennae. Allozyme studies indicate that these distinct morphs are only remotely related, the alpine transparent group being closer to lowland, likewise transparent, populations. A melanic population found at Svalbard is closely related to the melanic mainland populations. Clonal diversity in ponds and shallow lakes is very low, in contrast to populations of deeper lakes.