Temperature preferences of the mite, Alaskozetes antarcticus, and the collembolan, Cryptopygus antarcticus from the maritime Antarctic

The thermal preferences of Alaskozetes antarcticus (Acari, Cryptostigmata) and Cryptopygus antarcticus (Collembola, Isotomidae) were investigated over 6 h within a temperature gradient (−3 to +13 °C), under 100% relative humidity (RH) conditions. After 10 days of acclimation at −2 or +11 °C, individual supercooling points (SCP) and thermopreferences were assessed, and compared with animals maintained for 10 days under fluctuating field conditions (−6 to +7 °C). Acclimation at −2 °C lowered the mean SCP of both A. antarcticus (−24.2 ± 9.1) and C. antarcticus (−14.7 ± 7.7) compared to field samples (−19.0 ± 9.0 and −10.7 ± 5.2, respectively). Acclimation at +11 °C increased A. antarcticus mean SCP values (−13.0 ± 8.5) relative to field samples, whereas those of C. antarcticus again decreased (−16.7 ± 9.1). Mites acclimated under field conditions or at +11 °C selected temperatures between −3 and +1 °C. After acclimation at −2 °C, both species preferred +1 to +5 °C. Cryptopygus antarcticus maintained under field conditions preferred +5 to +9 °C, whereas individuals acclimated at +11 °C selected +9 to +13 °C. For A. antarcticus, thermopreference was not influenced by its cold hardened state. The distribution of field specimens was further assessed within two combined temperature and humidity gradient systems: (i) 0–3 °C/12% RH, 3–6 °C/33% RH, 6–9 °C/75% RH and 9–12 °C/100% RH and (ii) 0–3 °C/100% RH, 3–6 °C/75% RH, 6–9 °C/33% RH and 9–12 °C/12% RH. In gradient (i), C. antarcticus distributed homogeneously, but, in gradient (ii), C. antarcticus preferred 0–3 °C/100% RH. Alaskozetes antarcticus selected temperatures between 0 and +6 °C regardless of RH conditions. Cryptopygus antarcticus appears better able than A. antarcticus to opportunistically utilize developmentally favourable thermal microclimates, when moisture availability is not restricted. The distribution of A. antarcticus appears more influenced by temperature, especially during regular freeze-thaw transitions, when this species may select low temperature microhabitats to maintain a cold-hardened state.