The role of rapid cold hardening in protecting Drosophila melanogaster against damage from sublethal cold stress

Ectothermic animals, including insects, are reliant on the surrounding environment to maintain the internal temperature needed for metabolic processes. If the temperature drops too far, the animal will begin to accumulate potentially irreparable damage. While some cold stress can be mitigated through behavioral thermoregulation, many insects have evolved physiological responses to protect against cold damage. Rapid cold hardening (RCH) is one such process. A short exposure to a low temperature increases survival upon subsequent exposure to a normally lethal temperature. While much work has focused on the effect of RCH at lethal temperatures, there has been less work on whether RCH also protects against sublethal damage. This study provides additional insight into the complexity of rapid cold hardening responses in insects. Drosophila were exposed to an RCH treatment of 4°C followed by a sublethal cold shock of -2°C. Drosophila were assayed for reproduction, tissue damage, metabolites, activity, and respiration following the cold shock. We found that RCH conserves reproduction in males but not females. RCH protects against tissue damage, particularly in females. While activity and respiration were not significant, there are patterns indicating differing responses to a cold shock preceded by rapid cold hardening. Although RCH did not protect against all types of cold stress damage, preserving reproductive capability and minimizing tissue damage indicate that RCH can protect against some sublethal cold damage.