M. Holmstrup et P. Westh, EFFECTS OF DEHYDRATION ON WATER RELATIONS AND SURVIVAL OF LUMBRICID EARTHWORM EGG CAPSULES, Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, 165(5), 1995, pp. 377-383
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.