EFFECTS OF DEHYDRATION ON WATER RELATIONS AND SURVIVAL OF LUMBRICID EARTHWORM EGG CAPSULES

Earthworm egg capsules of five species were compared with regard to su rvival and water relations upon exposure to controlled dehydration at 20 degrees C. Cocoons of the investigated species all contained about 3.5 g water g(-1) dry weight when fully hydrated. Approximately 18% of this does not readily freeze upon cooling to -40 degrees C and is ref erred to as osmotically inactive water, Cocoons exposed to desiccation lose a large proportion of the osmotically active water over 1-4 days until water in the cocoon fluids has equilibrated with surrounding wa ter vapour. The amount of osmotically inactive water, on the other han d, is only reduced by 10-20%. Dendrobaenn octaedra was the species mos t tolerant to drought, its tolerance limit coinciding with loss of pra ctically all osmotically active water. For the five species investigat ed, there seemed not to be any clear correlation between drought toler ance and microhabitat. Previous investigations have suggested a very c lose relation between tolerance to dehydration and to subzero temperat ures in overwintering earthworm cocoons. Survival at a given level of dehydration at room temperature is less than at temperatures below 0 d egrees C, and the tolerance of room temperature dehydration is not clo sely correlated with cold hardiness across the range of the species st udied.