Seasonal changes in tolerance to cold and desiccation in Phauloppia sp (Acari, Oribatida) from Finse, Norway

In the alpine region at Finse, Norway, Phauloppia spp. (Acari, Oribatida) i nhabit lichens on top of boulders. Adult mites are about 0.5 mm in length a nd have a mean weight of ca. 15 mu g. Temperatures in the lichens may drop below -35 degrees C in winter and increase to 55 degrees C in the summer. L arge seasonal variations were recorded in supercooling points and body flui d osmolality. Mean January values of SCPs and osmolality were -35.3 degrees C and 3756 mOsm, while July values were -9.4 degrees C and 940 mOsm, respe ctively. Thermal hysteresis proteins were present in both summer and winter acclimated mites. In mid-winter, some of the mites survived mole than 49 d ays in a water vapor saturated atmosphere at -19 degrees C, and more than 4 2 days enclosed in ice at the same temperature. The mites showed high tolerance to desiccation. Specimens collected in Octo ber survived up to 23 days at 22 degrees C and 5% RH. The tolerance to desi ccation was lower in specimens collected during the winter. Some mites surv ived the loss of up to 90% of their total water content and were reactivate d when given access to water. Length measurements of individual Phauloppia sp. showed that both male and female mites are clearly divided in two size groups, suggesting that they belong to two closely related species or diffe rent populations. (C) 2000 Elsevier Science Ltd. All rights reserved.