Effects of ingestion of liquids on the cold tolerance of an Antarctic mite
Samples of a cryptostigmatid mite, Alaskozetes antarcticus, were collected during summer and winter on Signy Island, South Orkney Islands, in the maritime Antarctic. In four experiments, adult mites were maintained at 4°C and 100% r.h. for periods of 14, 28 and 32 days. In two of these experiments the mites received cold-hardening pre-treatments at −15 and −20°C (56 and 21 days respectively). The experiments compared: (1) The effects of acclimation with and without access to distilled water, (2) the effects of liquid glucose (10% solution) and algal diets, in terms of cold hardiness (supercooling points and cryoprotectant levels). In one of the experiments, changes in live weight and body water content were determined. For cold-hardy mites, with high glycerol levels and low supercooling points, the distilled water and glucose treatments produced an extreme loss (about 20–25°C) of supercooling ability. When no liquid was available, only a small (about 4°C) loss occurred. Glycerol concentrations decayed in both cases. Non cold-hardy mites, with low glycerol levels and a wide range of supercooling points, did not show differing responses when acclimated at 4°C with and without distilled water, but exposure to glucose solution did result in extreme supercooling point elevations. These results are related to seasonal changes in Alaskozetes cold hardiness in the field, and are discussed in terms of hypotheses advocating external (bacterial and mineral) and internal (organic) sources of ice-nucleating agents.