| Popis: |
The Antarctic Peninsula is characterized by harsh and dynamic environmental conditions. Organisms inhabiting this environment may be challenged by extremes of low temperature, limited water availability, dramatic seasonal fluctuations of light availability and ultraviolet radiation, and high salinity. This dissertation describes three projects examining the tolerance and physiological responses to such environmental stress of two Antarctic arthropods, the midge Belgica antarctica and the collembolan Cryptopygus antarcticus. The first investigation examined the ability of B. antarctica larvae to resist inoculative freezing at subzero temperatures and instead dehydrate as a strategy for winter survival (i.e., cryoprotective dehydration). When cooled to subzero temperatures in the presence of ice, the body fluid melting point was depressed to near equilibrium with the ambient temperature, due to reductions of body water content and the accumulation of several osmolytes, suggesting larvae can undergo cryoprotective dehydration at subzero temperatures. Under more natural conditions, the use of cryoprotective dehydration versus freeze tolerance for winter survival appears to depend upon the moisture content of the surrounding soil. The purpose of the second study was to assess the tolerance and physiological response to desiccation of C. antarcticus under ecologically-relevant conditions. Slow dehydration at high relative humidities characteristic of the austral summer induced the accumulation of several organic osmolytes and increased the tolerance of water loss. A mild drought acclimation further increased the subsequent desiccation tolerance of C. antarcticus. The springtails were also susceptible to water loss at subzero temperatures and likely rely upon such dehydration as a key component for winter survival. As B. antarctica microhabitats may be periodically inundated with seawater, the final investigation examined the osmotic response and tolerance of larvae to hyperosmotic seawater exposure. The larvae displayed an impressive tolerance of the osmotic stress, as ~50% survived a 6-d submergence in pure seawater. Hyperosmotic stress induced the accumulation of organic osmolytes and resulted in a significant positive correlation between the rate of oxygen consumption and larval body water content. Finally, a brief seawater acclimation enhanced the subsequent tolerance of freezing and dehydration, but reduced the tolerance of heat shock. |
