Genetic differentiation among gammarid (Eulimnogammarus cyaneus) populations in Lake Baikal, East Siberia

Genetic differentiation of Eulimnogammarus cyaneus, a littoral gammaridean amphipod endemic to Lake Baikal, was investigated by allozyme analyses of 2 1 gene loci. Individuals from 29 sites around the entire lake were differen tiated into northern and southern population groups with a Nei's genetic di stance of 0.035 (G(st) = 0.020). The distribution of the two groups in the lake approximately corresponded with the bathymetric division between the n orth basin and the central and south basins. No notable physical barrier to prevent genetic mixing between the two groups is recognized in the lake at present, so the two groups should have been spatially isolated and then ge netically differentiated within this limnetic system through significant dr ops of lake level in the past. The two groups are now in close contact at a narrow area near Olkhon Strait along the west coast of the lake. Different ly colored individuals of this species appeared to form a panmictic populat ion in each habitat.