Acclimation, shock and hardening in the cold

Recent articles by Bowler [2005. J. Therm. Biol. 30, 125-130] and Loeschcke and Sørensen [2005. J. Therm. Biol. 30, 255-257] have discussed the relationship between acclimation, hardening and heat shock in ectothermic animals, implying that analogous processes occur at low temperatures. We address this implication using the Drosophila literature. Cold tolerance in Drosophila has been measured in response to hardening (usually 1-3 h) or acclimation (usually days-weeks) using at least 27 different duration-intensity combinations. The metrics of response to these treatments include chill coma recovery or onset, survival and measures of reproductive success. However, it is unclear whether the mechanisms underlying the different metrics are the same, or whether the causes of injury are related over duration-intensity exposures ranging from a few minutes to hundreds of days. Furthermore, whilst there is ample evidence for acclimation and cold hardening in Drosophila, there is no clear evidence for a cold-shock response analogous to the well-characterised heat-shock response.