Characterization of drought-induced rapid cold-hardening in the Antarctic midge, Belgica antarctica

Survival of the terrestrial midge, Belgica antarctica, on the Antarctic Peninsula is promoted, not only by their adaptations to prolonged exposures to seasonal stresses, but also by their ability to respond to unpredictable changes in their environments. Rapid cold-hardening (RCH) is an extremely swift acclimatory response of insects that occurs within minutes to hours. While the RCH response is most commonly induced by a brief exposure to mildly low temperatures, a similar rapid acclimatory response can also be elicited by exposure to drought. In this study, we characterized this drought-induced RCH in larvae of B. antarctica. Compared to fully hydrated larvae, those desiccated at various relative humidity (R.H.) conditions between 0 and 99% R.H. for 2 h had a significantly greater survival (~ 50%) to freezing at − 14 °C. The amount of water loss varied between 4 and 16% depending on R.H. conditions; however, all treatments were equally effective in eliciting the protective response against freezing stress, and its induction was evident within 30 min of desiccation. Lack of substantial changes in body-fluid osmolality or levels of major cryoprotectants suggest that accumulation of these protective solutes is not a primary mechanism of this response. Interestingly, the RCH protection induced by desiccation persisted after larvae were allowed to recover a significant portion of the lost water. Our results indicate that larval midges are highly sensitive to desiccation, capable of swiftly initiating physiological changes in response to a small reduction in their body water content.