Temperature and the hygropreference of the Arctic Collembolan Onychiurus arcticus and mite Lauroppia translamellata

The hygropreference of adult Onychiurus arcticus (Tullberg) was investigated over 2 h at 0, 10 and 20 degrees C, along humidity gradients (12-98% RH) established using different salt solutions. At all temperatures 0. arcticus preferred the highest humidity (98% KH). At 0 and 20 degrees C, saturated conditions were preferred to 98% RH. The hygropreference of the mite Lauroppia translamellata (Willmann) was also assessed at 20 degrees C, and no clear RH preference was observed. This species survived the loss of 24.9 +/- 2.1% of its initial water content when held for 24 h at 20 degrees C and 12% RH. A range of assays designed to eliminate the influence of thigmotactic behaviour and population clumping pen-nit exclusion of these factors as being responsible for the observed results. The mean initial water content of O. arcticus samples (71.7 +/- 10.9, 73.4 +/- 4.0 and 73.8 +/- 23.5% at 0, 10 and 20 degrees C, respectively) did not differ significantly between temperatures, indicating that the results were not influenced by differences in initial hydrated state. The percentage water loss of individuals within the gradient increased with temperature, and differed significantly between regimes. The ecological significance of the observed humidity preferences are discussed.