Combined effects of drought and cold acclimation on phospholipid fatty acid composition and cold-shock tolerance in the springtail Protaphorura fimata.

Terrestrial arthropods' ability to survive sub-zero winter temperatures is an important factor influencing their abundance and geographic distribution. It is, therefore, important to understand their physiological mechanisms of low-temperature survival. Acclimation to moderate-low temperature can improve cold tolerance, and pre-acclimation to mild desiccation can also improve survival of a subsequent cold exposure. However, very few studies have assessed the combined actions of cold and drought acclimations. In the present study, we combined cold acclimation with drought acclimation making it possible to assess the interactions between effects of these two stressors using the springtail Protaphorura fimata as a model organism. We investigated the interacting effects of drought and cold acclimation on body fluid osmolality, membrane phospholipid fatty acid (PLFA) composition, and cold-shock tolerance. Acclimation to mild drought (- 2.46 MPa) increased body fluid osmolality from 0.33 to 1.25 Osm at all acclimation temperatures (5, 10, 15, or 20 °C) likely due to accumulation of the compatible osmolytes, trehalose, and alanine. Interestingly, the expected positive effect of drought acclimation on cold-shock tolerance was only evident at high acclimation temperature (20 °C), whereas at intermediate temperatures (10 and 15 °C), there was an interaction between acclimation temperature and drought. At 5 °C, no effect of drought acclimation on cold-shock tolerance was observed despite high osmolality. The positive effect of drought acclimation at 20 °C on subsequent cold-shock survival coincided with a drought-induced effect on PLFA composition only detectable at high temperature. We discuss the possible roles of drought-induced compatible osmolytes and an altered PLFA composition in the cold-shock tolerance of arthropods.