Rapid cold hardening in Antarctic microarthropods

1. Rapid cold hardening was examined in three common Antarctic microarthrop ods using differential scanning calorimetry over timescales between 3 and 3 0 h, under field and controlled laboratory conditions. 2. In fresh field samples and cultures of the springtail, Cryptopygus antar eticus (Willem), and cultures of the mites, Alaskozetes antarcticus (Michae l) and Halozetes belgicae (Michael), maintained under summer field-simulati ng conditions, supercooling point (SCP) distributions tracked microhabitat temperature variation over the observation period. 3. Controlled acclimation of samples of summer-acclimatized C. antarcticus caused significant cold hardening after 12 h at temperatures around 0 degre esC (+3 to -2 degreesC). No response was obtained at higher or lower temper atures, or in field-fresh winter-acclimatized animals. The latter did not l ose cold hardiness when held at positive temperatures for 12 h. 4. Gradual cooling of C antarcticus over 20 h from +5 to -5 degreesC caused a considerable increase in cold tolerance. Rewarming partially but non-sig nificantly reversed this effect. The greatest response occurred between +3 and +1 degreesC. Maximum faecal pellet production also occurred in this int erval, but gut clearance alone was not sufficient to explain observed cold hardening. 5. It is hypothesized that these species possess a hitherto unrecognized ca pacity to alter cold hardiness in summer in response to environmental tempe rature cues over a shorter timescale than previously thought, by a mechanis m that relies on neither gut clearance nor concentration of body fluids via water loss. This ability may reduce the developmental costs of premature e ntry into an inactive, cold-hardy state.