Effects of low-temperature acclimation on the survival and cold tolerance of an antarctic mite
The effects of long-term exposures to constant temperatures (+4, 0, −5, −10, −15 and −20°C) on the survival of a cryptostigmatid mite, Alaskozetes antarcticus, were studied during 1983–1984 on Signy Island, South Orkney Islands, in the maritime Antarctic. Field-fresh samples collected during the austral summer showed very large (e.g. about 60 percentage points) variations in survival when placed at constant temperatures, as a result of collection-date effects. Pretreatment acclimations (10-day) at +4 and 0°C (especially) reduced this variation. Short-term modulations in cold-hardiness levels were related to ambient temperature fluctuations. However, samples collected on the same occasion, from microhabitats 20 m apart, also showed significant cold-hardiness variation. For twelve summer samples, survival after 24 h at −15°C was highly correlated with supercooling capacity. Winter samples showed little variation in survival, interms of collection-date. Percentage survival remained greater than 85% at −5, −10 and −15°C, for exposures up to 100 days. Samples with median supercooling points of about −30°C, showed 52% survival after 250 days at −15°C, and 73% survival after 100 days at −20°C. At −15°C, supercooling capacity was used up at an estimated rate of 0.06 deg day−1, as a result of a time-temperature interaction effect on the probability of heterogeneous nucleation. Adult mites showed 78% survival after 21 days encasement in distilled water ice, at −15°C. Survival differences between post-larval stages were not detected. In conclusion, survival ability under controlled laboratory conditions appeared to exceed the requirements of average winter-habitat temperatures, but the effects of fluctuating and extreme temperatures require investigation. Supercooling points are considered to be accurate indicators of low-temperature survival capability in this species.