Candidate gene expression associated with geographical variation in cryoprotective dehydration of Megaphorura arctica

A number of small and permeable invertebrates survive subzero temperatures by cryoprotective dehydration (CPD) in which animals readily lose water to equilibrate body fluid melting points with surrounding temperature thereby avoiding the risk of freezing. Population studies are useful for detecting evolutionary climatic adaptation by comparing populations from locations differing in climatic characteristics. To identify the existence of adaptive variation for important physiological mechanisms underlying the CPD capacity we investigated the gene expression profile of five candidate genes as well as water content and cryoprotectant concentrations in five natural populations from diverse climatic origins. Our results show that Arctic populations, originating from an area with severe winter conditions (Svalbard), respond differently than the populations coming from more benign conditions (Mainland Norway). The Svalbard populations lost water and accumulated trehalose faster in response to cold exposure at -6 °C. The gene expression results suggests that the Svalbard populations experience less cellular perturbation and has a lesser need for molecular chaperones (hsp70) during CPD, but handles the stress by early and rapid induction of cryoprotectant producing enzymes (tps) and oxidative stress scavengers (sod) and possibly also membrane modifications (fad). Thus, these traits relate to the severity of the climate adapted to and are likely markers of their adaptive history.