Increase in cold‐shock tolerance by selection of cold resistant lines in Drosophila melanogaster

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Abstract
In Drosophila melanogaster, the cold‐shock tolerance of adult flies at ‐7°C increased 22% after a prior 2h exposure to 4°C as measured by LD50, the dose (degree minutes of exposure to subzero temperature) which resulted in 50% mortality. Cold‐shock tolerance was further significantly increased by selecting cold resistant lines by exposure of adults (1) to 4°C for 2 h (short‐term chilling), or (2) to ‐7°C for 80–120 min (cold shock), or (3) to short‐term chilling followed by cold‐shock. After ten generations of selection, the greatest increase in cold‐shock tolerance was found in flies selected using the combined exposure of short‐term chilling and cold shock. LD50s increased 33% in comparison with the unselected control strain when no chilling pre‐treatment was given prior to cold shock at ‐7°C. The rapid cold‐hardening response increased 82% in the line selected by the short‐term chilling and cold‐shock regime. The enhanced cold‐shock tolerance was relatively stable since no decrease was observed after four generations without selection. This report shows the role of short‐term adaptation as well as selection in the capacity to survive low temperatures in non‐diapausing stages of insects.