P3.78 Saturday, Jan. 5 Salinity Tolerance in the Antarctic Midge: Seawater Acclimation Confers Cross Tolerance to Freezing and Dehydration ELNITSKY, M.A.*; BENOIT, J.B.; LOPEZ-MARTINEZ, G.; DENLINGER, D.L.; LEE, R.E.; Miami University; Ohio State University; Ohio State University; Ohio State University; Miami University email@example.com
Summer storms along the Antarctic Peninsula can result in larvae of the midge, Belgica antarctica, becoming periodically inundated with seawater from tidal spray. As microhabitats dry, larvae may be exposed to increasing concentrations of seawater. Alternatively, as a result of melting snow or following rain, larvae may be immersed in freshwater for extended periods. We assessed the tolerance and physiological response of B. antarctica larvae to salinity exposure, and examined the effect of seawater acclimation on tolerance of freezing, dehydration, and heat shock. Midge larvae tolerated extended exposure to hyperosmotic seawater; nearly 50% of larvae survived a 10-d exposure in seawater (~1000 mOsm kg-1) and ~25% of larvae survived 6 d in 2000 mOsm kg-1 seawater. Exposure in hyperosmotic seawater reduced body water content and increased hemolymph osmolality. Nearly all larvae survived a 10-d exposure in freshwater and isoosmotic seawater (~400 mOsm kg-1). A 3-d acclimation to seawater increased the survival of freezing relative to freshwater-acclimated larvae. Even after rehydration, the freezing survival of larvae acclimated in seawater was greater than freshwater-acclimated larvae. Additionally, seawater acclimation increased the larvae’s subsequent tolerance of dehydration. However, relative to freshwater-acclimated larvae, seawater acclimation reduced the tolerance of heat shock. These results suggest that the physiological response of B. antarctica larvae to osmotic perturbation may confer cross tolerance to other stressors and effect survival in the harsh and unpredictable Antarctic environment.