On tolerance of earthworm Eisenia nordenskioldi (Oligochaeta, Lumbricidae) for extremely low soil moisture in the northeast of Asia

The ability of invertebrates to survive droughts in their special capsules was studied by the example of the earthworm Eisenia nordenskioldi Eisen. This species is of wide valence; it colonized tundra, forest, and forest-steppe zones in Asia and party in Eastern Europe. The earthworms of this species were collected in late July and divided into 48 groups. Each group consisted of 6 individuals with similar mass (+/-5 mg). The samples were placed into glass tubes, closed by cotton-gauze plugs, and kept in darkness at room temperature. When soil dree, the animals stopped feeding, rolled themselves into balls (by 2-3 individuals) and formed capsules made of soil particles stuck by slime and excrements. Every 10 days, 12 individuals were tested for the water content, other 12, for glycogen, lipids, glucose, and polyols concentrations. In addition, soil moisture and temperature of earthworms' habitat were measured. The multiyear dynamics of the earthworms' number was monitored. E. nordenskioldi, like other earthworm species, is resistant to a short-term loss of water (to 50% of body mass) in the open air. When the soil moisture decreases down to 15-18%, this species forms capsules where it can stay for two months under a gradual fall of soil moisture down to 5%. Being in the capsules, the earthworms lost about 42% of their intial mass. The water content in tissues remained the same. Thus, capsules allow earthworms to support the water homeostasis of their bodies at the expense of the metabolic water produced in utilization of reserve substances. The adaptations described allow these animals to sustain a high water deficit in the environment and to inhabit not only their traditional mesophytic biotopes, but also periodically droughty expanding their range.