Cold hardiness in Entomobrya nivalis (Collembola, Entomobryidae): annual cycle of polyols and antifreeze proteins, and antifreeze triggering by temperature and photoperiod |
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Authors: | P Meier J Zettel |
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Institution: | Zoologisches Institut der Universit?t Bern, Baltzerstrasse 3, CH-3012 Bern, Switzerland Fax: +44-31/631?48 88, CH
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Abstract: | In the Swiss Prealps Entomobrya nivalis hibernates in an inactive state, hidden under bark flakes on spruce. For freeze avoidance it relies on thermal hysteresis
proteins (THPs) and polyols (mainly ribitol, with small amounts arabitol and threitol). Polyols are present only during the
inactive state, THPs additionally protect during the transition phase in spring and autumn, when animals are still active
but frosts may occur. Peak values were recorded in February/March for THPs (3.5 °C hysteresis between melting and freezing
point) and for polyols (26 μg mg−1 FW; hemolymph osmolality 680 mosmol l−1). E. nivalis is able to control its hemolymph osmolality independently of body water content. Mean osmolality in summer was 350– 440 mosmol l−1, in winter it was elevated to 650 mosmol l−1, due to a synthesis mainly of ribitol. Body water content varied between 1.8 and 3.3 mg H2O mg−1 DW, depending on humidity conditions. Experiments on triggering of antifreeze synthesis showed the action of temperature
and photoperiod as cues, but there was also evidence for an endogenous rhythm. No clear correlation between antifreeze concentration
and supercooling ability could be established, suggesting that gut content or other parameters also play an inportant role.
Accepted: 18 November 1995 |
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Keywords: | Collembola Entomobrya nivalis cold hardiness antifreezes osmoregulation triggering |
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