A comparative study of patterns of water loss from two Antarctic springtails (Insecta, Collembola)
Dehydration experiments were conducted on individual Collembola at 0% relative humidity with the temperature ramped from 5 to 34°C at the rate of 0.5°C min−1. Continuous records of weight loss with time were made using an electrobalance. In both Parisotoma octooculata and Cryptopygus antarcticus, the rate of water loss increases with temperature and time. Parisotoma dehydrates faster than Cryptopygus under similar conditions when the evaporative flux reaches a smaller peak earlier in the former species. The slope of the relationship of conductance (of water vapour) to the evaporative driving force (vapour density deficit) is linear over a wide range, and is not significantly different in the two springtails although the conductance of Parisotoma is significantly higher than that of Cryptopygus. The conductance is inversely related to the vapour density deficit in Cryptopygus during the initial 10 min drying period, and in both species at similar low water contents (after 34 min in Parisotoma and 50 min in Cryptopygus). Cryptopygus contains a significantly greater weight of water (10 μg) than Parisotoma, and this combined with lower conductance values determines its slower rate of dehydration under the experimental conditions. The results are discussed in relation to simultaneous heat and mass transfer processes in porous solids, and with regard to the ecology of these Collembola. Field data show that Cryptopygus has a higher water content than Parisotoma throughout the year, and the experimental data support the observed distributions of these species in the maritime Antarctic.
Authors: Block, William, Harrisson, Paul M., Vannier, Guy