GROWTH AND SURVIVAL STRATEGY OF THE ANTARCTIC MITE ALASKOZETES ANTARCTICUS

Growth and mortality rates of three juvenile instars and adults of the oribatid mite Alaskozetes antarcticus were measured over a twelve month period using field enclosures in its maritime Antarctic habitat. A pattern was found of rapid growth during the short summer period (0.2-0.4 mu g dry weight increment per day) followed by gradual weight loss overwinter. Most individuals completed one instar per year, reaching a premoult resting phase by late summer, with the moult being delayed and relatively synchronised early the next summer. A small proportion of proto- and deutonymphs completed two moults within one summer period. After the final moult adults over-wintered again before commencing oviposition, suggesting that the life cycle (egg-egg) will take at least five years. Mortality was not biased towards any instar or time of year. Highest individual growth rates were obtained at a constant temperature of 7 degrees C in the laboratory. However, experimental increase of mean field temperature from 2.7 to 4.3 degrees C by use of a plastic cloche led to decreased growth, although no change in moulting frequency or mortality rate. Laboratory survival was greatest at 2 degrees C and decreased with increasing temperature. Alaskozetes antarcticus may be described as 'a' (adversity) selected, showing an exceptionally long life cycle of five to six years and extensive physiological investment in survival adaptations. Moult synchronisation in early summer, involving entering winter in the inactive premoult phase, will increase overwinter survival by reducing the chance of inoculative freezing from gut contents, and may be advantageous in maximising the time available for feeding during the subsequent summer, or ensuring proximity of the sexes after the final moult.