NOTES ON THE ECOLOGY AND PHYSIOLOGY OF THE ANTARCTIC ORIBATID MITE MAUDHEIMIA-WILSONI

The oribatid mite Maudheimia wilsoni Dalenius was found to be numerous on the underside of stones at Jutulsessen (72-degrees-S, 3-degrees-E) in Dronning Maud Land, Antarctica. Daily temperature fluctuations of the microhabitat from as high as 19-degrees-C and to as low as -17-deg rees-C were observed during the austral summer. Optimal activity of th e mites occurred at 10-degrees-C. Even in January the mean supercoolin g point of adult mites was as low as - 30.8 +/- 4.7-degrees-C. Haemoly mph osmolality ranged from 500 to 800 mOsmol and thermal hystersis fre ezing points from -4.7 to - 6.1-degrees-C. Adult mites had a mean wate r content of 43.6% and a water loss rate of 0.12 mug h-1 at 15-degrees -C and 10% relative humidity.