THE COLD-HARDINESS AND GEOGRAPHIC DISTRIBUTION OF EARTHWORMS (OLIGOCHAETA, LUMBRICIDAE, MONILIGASTRIDAE)

The cold-hardiness of 12 species and 2 subspecies of earthworms from Northern Eurasia was studied. Supercooling temperatures, the water content and the thresholds of tolerated temperatures of earthworms and their cocoons were determined. Threshold values varied within -1...-35 degrees C for earthworms, -1...-196 degrees C for cocoons. Earthworms of 4 species and 2 subspecies survived freezing. Cocoons of all species except Eisenia fetida were cold-tolerant. During wintering at subzero temperatures, earthworms lost up to 20 % of water, cocoons up to 37 %. Species of the same life form can overwinter at different stages and have different cold-hardiness values. On the whole, litter and soil-litter species (except for Eisenia fetida) were more resistant to cold compared to endogean ones. The following preliminary classification of earthworms according to their tolerance to negative temperatures has been worked out: 1) both onthogenetic phases are tolerant; 2) only cocoons are tolerant; 3) both onthogenetic phases are intolerant. The geographic distribution of all studied species (except for Eisenia nordenskioldi nordenskioldi) is partially or completely limited by an insufficient resistance of the worm's phase to negative temperatures. A significant cold-hardiness of cocoons of most species is non-adaptive, as worms hatched from the eggs in the spring die having not enough time to reach sexual maturity and to lay cocoons before the onset of subzero temperatures. Only 3 species (Eisenia nordenskioldi nordenskioldi, Eisenia atlavinyteae, Dendrobaena octaedra) can live in permafrost regions, this being the main reason for a drastically reduced diversity of earthworm assemblages in eastern Siberia (except for its southern, montane parts). In general, reasons for the impoverishment lie in modern climatic conditions correlated to ecophysiological capacities of the earthworms.