Experimental studies of ice nucleation in an Antarctic springtail (Collembola, Isotomidae)

Ice nucleation was studied in field-fresh and acclimated (4 degreesC withou t food for 11-20 days) samples of the springtail Cryptopygus antarcticus Wi llem (Collembola. Isotomidae) at Rothera Research Station. Adelaide Island on the Antarctic Peninsula. Ice nucleator activity (INA) was measured by a freezing droplet technique in addition to supercooling point (SCP) profiles and polyol, sugar, and water contents. Field and acclimated samples showed bimodal SCP distributions with a distinct high group (HG, mean SCP -8 to - 10 degreesC) and low group (LG: mean SCP - 23 to - 25 degreesC), which wer e significantly different. Acclimation at 4 degreesC increased the proporti on of individuals in the LG relative to that in the HG without significant effects on the mean SCP of both groups. INA of the HG was significantly gre ater than that of the LG. and acclimation further reduced the INA of the LG . The number of active ice nucleator agents (INAs) calculated for the HG of field samples increased by 23-100 times over the temperature range - 5 to - 8 degreesC compared to only 7 times for the LG over the same range. These differences were accentuated in the acclimation experiments. Glucose and g alactose were the main carbohydrates in both field and acclimated springtai ls, with the latter compound occurring in almost twice the concentration in the LG compared with that in the HG. Acclimation reduced the concentration of both compounds (glucose by 77% and galactose by 54%). whereas water con tent increased significantly. Digestion of food may have continued during a cclimation at 4 degreesC, which could reduce the LG INA. Lowering of temper ature over time is more likely to elicit a cold hardening response than con stant temperature acclimation. INA numbers calculated at the nucleation tem peratures for C. antarcticus samples were higher in the LG than in the HG. However, inactivation of INAs may be a key mechanism underlying cold harden ing in this species, either by sequestration within the cellular matrix or by being only seasonally active. (C) 2001 Academic Press.