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 mon th 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 perio d. After the final moult adults over-wintered again before commencing oviposition, suggesting that the life cycle (egg-egg) will take at lea st five years. Mortality was not biased towards any instar or time of year. Highest individual growth rates were obtained at a constant temp erature of 7 degrees C in the laboratory. However, experimental increa se of mean field temperature from 2.7 to 4.3 degrees C by use of a pla stic cloche led to decreased growth, although no change in moulting fr equency or mortality rate. Laboratory survival was greatest at 2 degre es C and decreased with increasing temperature. Alaskozetes antarcticu s may be described as 'a' (adversity) selected, showing an exceptional ly long life cycle of five to six years and extensive physiological in vestment in survival adaptations. Moult synchronisation in early summe r, involving entering winter in the inactive premoult phase, will incr ease overwinter survival by reducing the chance of inoculative freezin g from gut contents, and may be advantageous in maximising the time av ailable for feeding during the subsequent summer, or ensuring proximit y of the sexes after the final moult.