Rapid cold-hardening of Drosophila melanogaster (Diptera: Drosophiladae) during ecologically based thermoperiodic cycles.
In contrast to most studies of rapid cold-hardening, in which abrupt transfers to low temperatures are used to induce an acclimatory response, the primary objectives of this study were to determine (i) whether rapid cold-hardening was induced during the cooling phase of an ecologically based thermoperiod, (ii) whether the protection afforded was lost during warming or contributed to increased cold-tolerance during subsequent cycles and (iii) whether the major thermally inducible stress protein (Hsp70) or carbohydrate cryoprotectants contributed to the protection afforded by rapid cold-hardening. During the cooling phase of a single ecologically based thermoperiod, the tolerance of Drosophila melanogaster to 1 h at -7 degrees C increased from 5 +/- 5% survival to 62.5 +/- 7.3% (means +/- S.E.M., N=40-60), while their critical thermal minima (CTmin) decreased by 1.9 degrees C. Cold hardiness increased with the number of thermoperiods to which flies were exposed; i.e. flies exposed to six thermoperiods were more cold-tolerant than those exposed to two. Endogenous levels of Hsp70 and carbohydrate cryoprotectants were unchanged in rapidly cold-hardened adults compared with controls held at a constant 23 degrees C. In nature, rapid cold-hardening probably affords subtle benefits during short-term cooling, such as allowing D. melanogaster to remain active at lower temperatures than they otherwise could.
Kelty
J D
JD
Department of Zoology, 212 Pearson Hall, Miami University, Oxford, OH 45056, USA. j-kelty@uchicago.edu
Lee
R E
RE
D000064:Acclimatization; D000375:Aging; D000818:Animals; D050260:Carbohydrate Metabolism; D003080:Cold Temperature; D003451:Cryoprotective Agents / Q000378:metabolism; D004331:Drosophila melanogaster / Q000502:physiology*; D005260:Female; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006358:Hot Temperature; D008297:Male; D010507:Periodicity; D012727:Sex Characteristics
D003451:Cryoprotective Agents; D018840:HSP70 Heat-Shock Proteins