FEEDING STRATEGY OF EARTHWORMS IN MOUNTAIN PERMAFROST SOILS

The effect of temperature of the feeding activity of earthworms inhabiting the mountain permafrost soils was studied in the Upper Kolyma region (Magadan district). Experimental studies were carried out on a polyploid form Eisenia nordenskioldi (Eisen) (Lumbricidae, Oligochaeta), the only lumbricid species occurring in natural habitats of this region. Earthworms were acclimated in the laboratory to various temperatures from 1 to 25-degrees before estimating the feeding activity. The population of E. nordenskioldi under study showed the normal feeding patterns in the temperatures range 10-25-degrees with the maximum food consumption at 15-20-degrees. The daily food consumption in the optimum temperature zone averaged 800-1000 mg/g body mass, while the time of food passage through the digestive tract amounted to 6-7 h. As compared with the other geographical populations, the Kolyma population is characterized by a wide temperature range of feeding activity and by a shift of their optimum zone to the upper threshold of the normal life activity for the earthworms. Specific features of feeding of the Kolyma population are discussed with special reference to the hydrothermal conditions of the earthworm microhabitats. The feeding strategies of the E. nordenskioldi population from the Upper Kolyma mountain soils, Arctic tundra of the Taimyr peninsula and forest soil of the temperature zone are compared.