Ecophysiological strategies of Antarctic intertidal invertebrates faced with freezing stress

Recent studies have revealed a previously unanticipated level of biodiversity present in the Antarctic littoral. Here, we report research on the ecophysiological strategies adopted by intertidal species that permit them to survive in this environment, presenting cold-tolerance data for the widest range of invertebrates published to date from the Antarctic intertidal zone. We found significant differences in levels of cold tolerance between species within this zone. However, and contrary to expectations, intraspecific comparisons of subtidal and intertidal groups of eight species found significant differences between groups in only three species. One species, the nemertean Antarctonemertes validum, showed evidence of the presence of antifreeze proteins (thermal hysteresis proteins), with 1.4°C of thermal hysteresis measured in its haemolymph. We found a strong inverse relationship across species between mass and supercooling point, and fitted a power law model to describe the data. The scaling exponent (0.3) in this model suggests a relationship between an animal’s supercooling point and its linear dimensions

Tergipes antarcticus (Gastropoda, Nudibranchia): distribution, life cycle, morphology, anatomy and adaptation ot the first mollusc known to live in Antarctic sea ice

Tergipes antarcticus (Gastropoda, Nudibranchia) has been reported from Antarctic sea ice twice (1903 and 2008). The extent of its distribution and life history remained unclear. We have evaluated data from several cruises, showing that T. antarcticus is widely distributed in sea ice throughout the Weddell Sea. Adults, juveniles, larvae and egg clutches of T. antarcticus were found in the ice indicating that the species reproduces within this habitat. We collected live material of T. antarcticus for a thorough description of all life stages and to investigate the developmental stages and physiological adaptations. Total developmental time from egg to veliger larvae was relatively short with 31 days (range 13–65 days) at 0°C. Liquid withdrawn from egg clutches and adult T. antarcticus showed clear signs of thermal hysteresis. This is the first report of thermal hysteresis from a sea ice metazoan. We conclude that T. antarcticus is an autochthonous species to Antarctic sea ice

Acquisition of freeze protection in a sea-ice crustacean through horizontal gene transfer?

Sea ice is permeated by small brine channels, which are characterised by sub-zero temperatures and varying salinities. Despite sometimes extreme conditions a diverse fauna and Xora thrives within the brine channels. The dominant calanoid copepods of Antarctic sea ice are Stephos longipes and Paralabidocera antarctica. Here, I report for the Wrst time thermal hysteresis (TH) in the haemolymph of a crustacean, S. longipes, whereas P. antarctica has no such activity. TH, the non-colligative prevention of ice growth, seems to enable S. longipes to exploit all available microhabitats within sea ice, especially the surface layer, in which strong temperature Xuctuations can occur. In contrast, P. antarctica only thrives within the lowermost centimetres of sea ice, where temperature Xuctuations are moderate. S. longipes possesses two isoforms of a protein with TH activity. A high homology to a group of (putative) antifreeze proteins from diatoms, bacteria and a snow mold and, in contrast, no homologs in any metazoan lineage suggest that this protein was obtained through horizontal gene transfer (HGT). Further analysis of available sequence data from sea-ice organisms indicates that these antifreeze proteins were probably transferred horizontally several times. Temperature and salinity Xuctuations within the brine channel system are proposed to provide “natural transformation” conditions enabling HGT and thus making this habitat a potential “hot spot” for HGT