Physiological and Molecular Mechanisms of Stress Tolerance in a Polar Insect

Polar terrestrial environments are often described as deserts, where water availability is recognized as one of the most important limits on the distribution of terrestrial organisms. Global warming has further impacted the extreme thermal and hydric conditions experienced by Antarctic terrestrial plant and arthropod communities, especially as a result of glacial retreat along the Antarctic Peninsula. Within this context we focused our attention on thermal and hydric adaptations in the terrestrial midge, Belgica antarctica, the largest and most southerly holometabolous insect living in this challenging and changing environment. Overwintering midge larvae encased in the frozen substrate must endure desert-like conditions for more than 300 days since free water is biologically unavailable as ice. During the summer, depending on the vagaries of precipitation, wind, temperature and insolation, larvae may be immersed in melt water or detrital outwash from penguin rookeries and seal wallows, in addition to saltwater splash. During the past four years we made considerable progress in defining microclimatic conditions experienced by the larvae, and characterized larval and adult responses to thermal, hydric and osmotic stress at molecular levels. We demonstrated that larvae maintain constitutively elevated levels of heat shock proteins and have the capacity to undergo cryoprotective dehydration, the first demonstration in a true insect. We also discovered a novel role for the rapid cold-hardening response by showing that it increases freezing tolerance in larvae of B. antarctica. Using genomic and proteomic approaches we identified more than 90 genes that are uniquely expressed in response to dehydration, making it one of the best-known polar organisms from a molecular perspective.