MOISTURE RELATIONSHIPS OF THE HIGH ARCTIC COLLEMBOLAN ONYCHIURUS-ARCTICUS

Rates of desiccation, rehydration and survival, under conditions of 0 and 100% relative humidity, were investigated in the high arctic colle mbolan Onychiurus arcticus (Tullberg) over a range of temperatures fro m -3 to 10-degrees-C. Desiccation, measured over 4h in a dry environme nt, was rapid and highly significantly correlated with saturated vapou r pressure deficit (SVPD). At 10-degrees-C animals lost over 60% of bo dy moisture in under 1 h. Under moist conditions body weight remained constant. Survival, measured over 4h under dry conditions, showed a hi ghly significant negative correlation with SVPD across the range of te mperatures. Survival in moist controls was 100%. Partially desiccated animals were able to rehydrate using free water or moisture from a sat urated atmosphere, but uptake of the former was faster. Rates of water uptake were around 30 times slower than rates of loss through desicca tion. Animals given free water regained initial weights in 24-144h, de pendent on temperature. Uptake rates of free water, measured over the time necessary fully to rehydrate, were highly significantly correlate d with temperature, whereas those for atmospheric moisture were not. O ver the time scales used in the experiments, three linear regression e quations accurately predict rates of desiccation, rehydration and surv ival from SVPD or temperature. Ecological adaptation by O.arcticus to the highly contrasting climatic environments of the arctic summer and winter seasons is discussed in the context of climate change.