The impact of salinity exposure on survival and temperature tolerance of the Antarctic collembolan Cryptopygus antarcticus

The collembolan Cryptopygus antarcticus Willem is potentially exposed to habitat salinities equal to (or greater than) sea water, as a result of sea spray, drying of littoral habitats, dispersal or temporary entrapment on the surface of sea water, or exposure to localized salt deposits from dense vertebrate populations on terrestrial habitats. To test the impact of this exposure on C. antarcticus, the tolerance of the collembolan to being placed on the surface of sea water and solutions of higher salt concentrations is investigated. The effects of acclimation to exposure to liquids of different salinities [44, 100 and 200 parts per thousand (ppt) sea salt] on cold and heat tolerance, as well as thermal activity thresholds, are also explored. Cryptopygus antarcticus shows >75% survival after 10days of exposure to both sea water and 100-ppt salt, whereas it exhibits significantly lower survival after 5days (60% survival) and 10days (40%) of exposure to a 200-ppt solution. Body water content also decreases after exposure to all salinities, and particularly to the 200-ppt solution, in which>50% of body water is lost after 10days. Acclimation results in greater cold tolerance, although heat tolerance at 33, 35 and 37°C is either unaltered or reduced. The thermal activity thresholds of C. antarcticus at both high and low temperatures are also negatively affected by saline exposure. The data demonstrate the capacity of C. antarcticus to tolerate periods of exposure to saline conditions, and also show that this exposure can enhance cross-tolerance to low temperatures. The present study also demonstrates that salinity-associated stress at moderately low and high temperatures narrows the thermal range of activity, thus reducing the ability of collembolans to forage, develop and reproduce.