THERMAL ADAPTATION IN THE ARCTIC COLLEMBOLAN ONYCHIRUS-ARCTICUS (TULLBERG)

Ecophysiological characteristics, including survival at high and low temperatures, locomotory activity at sub-zero temperatures, supercooling ability and oxygen consumption rates, were investigated for the Arctic springtail Onychiurus arcticus (Tullberg) (Collembola, Onychiuridae). Individuals had a mean (+/- SE) fresh weight of 428.2 +/- 107.6 mu g which contained 74.0 +/- 10.2% body water. Survival at high temperatures was humidity dependent. After 3 h exposure at 100% relative humidity and 30 degrees C, >80% of the animals survived, but at >32.5 degrees C no individual survived. 70% of the animals survived a Ih exposure at 32.5 degrees C but at 35.0 degrees C all animals died. At 0% relative humidity there were no survivors after 3 h at >25.0 degrees C. At sub-zero temperatures, 60% of the springtails survived for 84 days at -3.0 degrees C, but at -5.0 degrees C survival was reduced to 35%. Individual collembolans showed locomotor activity down to -4 degrees C. O. arcticus was freezing-intolerant and individuals supercooled to -6.1 +/- 0.1 degrees C before freezing. This relatively high mean. (SE) supercooling point was stable throughout summer and was unaffected by acclimation temperature. A non-linear relationship existed between oxygen consumption and temperature. Between 0 and 10 degrees C the Q(10) was high at 7.0. It declined to 1.6 over the temperature range 10 to 30 degrees C, increasing to 5.8 at higher temperatures. O. arcticus possesses ecophysiological characteristics suited to life in the upper layer of soil and surface vegetation, and beneath snow cover. However, it appears to be poorly adapted to survive severe winter temperatures being intolerant of freezing and with little supercooling ability. Such features may restrict its present distribution in the Arctic, but it seems likely that it would benefit by an increase in environmental temperature.