Aspects of the environmental physiology of an antarctic terrestrial mite.

The physiological adaptations enabling the terrestrial mite Alaskozetes antarcticus (Michael) (Acari: Cryptostigmata) to inhabit the maritime Antarctic environment at Signy Island, South Orkney Islands, were investigated by experiments on animals cultured in the U.K. Log10 individual oxygen consumption rate was linearly related to log10 live weight and metabolic rate (oxygen consumption per unit live weight) was related to the reciprocal of the absolute temperature by the Arrhenius equation. Alaskozetes possesses a higher metabolic rate than comparable temperate species, measured at the same temperature, and is thereby enabled to remain active at temperatures that would immobilize temperate forms. A low activation energy for certain reactions may be responsible for metabolic rate elevation. Alaskozetes lacks the ability to regulate its metabolic rate in response to diurnal or seasonal temperature fluctuations. This is considered to enable the maximal utilization of higher temperatures for activity, feeding and growth and the conservation of metabolic reserves at low temperatures. Starvation, food materials, oxygen concentration and length of culture period are among the other factors affecting oxygen consumption rates in Alaskozetes. Freezing is fatal in Alaskozetes; winter survival occurs by means of supercooling and absence of ice formation in the tissues. The capacity to supercool extensively is dependent on the absence of gut contents containing efficient ice nucleating agents. Low acclimation temperatures prevent feeding and thereby promote supercooling. Supercooling ability is also increased by glycerol production in response to low temperature or low relative humidity, since glycerol concentration and supercooling points (temperatures of spontaneous body freezing) are linearly and inversely related. The ability to avoid freezing by supercooling and the use of low temperature as a cue for the development of increased cold tolerance are of considerable survival value in the field. The concept of adaptation is discussed with illustrations drawn from the results of the present research on Alaskozetes.