Monday, December 11, 2006

Cryoprotective dehydration and inoculative freezing in the Antarctic midge, Belgica antarctica

Michael A. Elnitsky, elnitsma@muohio.edu1, Scott A. L. Hayward2, Joseph P. Rinehart, rineharj@fargo.ars.usda.gov3, Luke H. Sandro1, David L. Denlinger, denlinger.1@osu.edu4, and Richard E. Lee1. (1) Miami University, Department of Zoology, 212 Pearson Hall, Oxford, OH, (2) Liverpool University, School of Biological Sciences, Crown Street, Liverpool, United Kingdom, (3) USDA-ARS, Insect Genetics and Biochemistry Research Unit, Biosciences Research Lab, 1605 Albrecht Blvd, Fargo, ND, (4) Ohio State University, 470 Aronoff Laboratory, 318 West 12th Avenue, Columbus, OH

During winter, larvae of the Antarctic midge, Belgica antarctica, must endure 7-8 months of continuous subzero temperatures, encasement in a matrix of soil and ice, and severely desiccating conditions. This environment, along with the fact that larvae possess a high rate of water loss and are extremely tolerant of desiccation, may promote the use of cryoprotective dehydration as a strategy for winter survival. Therefore, the purpose of the present study was to investigate the capacity of larvae to resist inoculative freezing and undergo cryoprotective dehydration at subzero temperatures. Slow cooling to -3oC in an environment at equilibrium with the vapor pressure of ice reduced larval water content by ~35% and depressed the body fluid melting point more than 3-fold to -2.6oC. At day fourteen of the subzero exposure, larval survival was >95%, suggesting larvae have the capacity to undergo cryoprotective dehydration. The ability of larvae to resist inoculative freezing and utilize a strategy of cryoprotective dehydration was significantly affected by soil moisture content. The percentage of larvae that resisted inoculative freezing, as detected by a reduction of larval water content during slow cooling to -3oC, decreased with increasing soil moisture. These results suggest that larvae of the Antarctic midge have the capacity to resist inoculative freezing at relatively low soil moisture contents and undergo cryoprotective dehydration.

Species 1: Diptera Chironomidae Belgica antarctica (Antarctic midge)