Speed of exposure to rapid cold hardening and genotype drive the level of acclimation response in Drosophila melanogaster

Comparing methodologies that attempt to mimic natural conditions is important when evaluating thermal tolerances of ectotherms, as exposing animals to different artificial thermal regimes may provide conflicting information of an insect's thermal profile. Rapid cold hardening (RCH) occurs in ectotherms and typically increases survivorship to extreme cold exposure through a short, pre-treatment to a non-lethal cold temperature. Here we assess survivorship in a set of genotypes from the Drosophila melanogaster Reference Panel for direct and ramping RCH pre-treatments at cooling rates occurring under more natural conditions (0.1 °C/min and 0.5 °C/min) in combination with a direct and ramped rewarming treatment post cold exposure. We find that all three pre-treatment exposures alone significantly increase survivorship. We find significant correlations in survivorship among treatments across genotypes, suggesting that regardless of the pre-treatment, individuals of a given genotype have an innate level of acclimation. When rewarming is introduced, survivorship significantly decreased relative to pre-treatment alone and correlations of survival between phenotypes were not significant. Our results suggest that rewarming and slow RCH are costly to survival while a quicker RCH may impart physiological benefits more consistently across genotypes.