Rapid cold hardening in Antarctic microarthropods

1 Rapid cold hardening was examined in three common Antarctic microarthropods using differential scanning calorimetry over timescales between 3 and 30 h, under field and controlled laboratory conditions. 2 In fresh field samples and cultures of the springtail, Cryptopygus antarcticus (Willem), and cultures of the mites, Alaskozetes antarcticus (Michael) and Halozetes belgicae (Michael), maintained under summer field-simulating 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 °C (+3 to −2 °C). No response was obtained at higher or lower temperatures, or in field-fresh winter-acclimatized animals. The latter did not lose cold hardiness when held at positive temperatures for 12 h. 4 Gradual cooling of C. antarcticus over 20 h from +5 to −5 °C caused a considerable increase in cold tolerance. Rewarming partially but non-significantly reversed this effect. The greatest response occurred between +3 and +1 °C. Maximum faecal pellet production also occurred in this interval, but gut clearance alone was not sufficient to explain observed cold hardening. 5 It is hypothesized that these species possess a hitherto unrecognized capacity to alter cold hardiness in summer in response to environmental temperature cues over a shorter timescale than previously thought, by a mechanism that relies on neither gut clearance nor concentration of body fluids via water loss. This ability may reduce the developmental costs of premature entry into an inactive, cold-hardy state.

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