Introduction

More than any other habitat on earth, Antarctica is a unique natural laboratory, ideal for studying temperature adaptations. Hence special attention will be given to its paleogeography and to the adaptive mechanisms of Antarctic marine organisms. For example some adaptations (freezing avoidance, efficient enzymatic catalysis and cytoskeletal polymer assembly, decreased blood viscosity through reduction or elimination of erythrocytes and haemoglobin) represent a unique character of Antarctic fish and will be examined in detail. Specialisations in haematology and in the oxygen transport system were also developed by other polar and temperate organisms: Arctic mammals (reindeer, musk ox, whale), birds (penguin), reptiles (turtle), crustaceans (krill), cephalopods (squid). We describe the molecular mechanisms of the oxygen transport system in relation to requirements for function at low temperature.

It is pertinent to mention the difficulty in establishing consensus on objective criteria to identify a phenotypic trait as an adaptation. Thus, adaptation remains ‘a slippery concept’. The reader will find extensive discussion on this and other issues in two recent reviews (Reeve & Sherman, 1993; Garland & Carter, 1994).

The Antarctic

In the late Precambrian, 590 million years ago (Ma), Antarctica was the central part of the supercontinent Gondwana, which remained intact for 400 million years, during the Paleozoic and part of the Mesozoic, through the Jurassic; fragmentation began and continued during the Cretaceous. The continental drift took Antarctica to its present position about 65 Ma, at the beginning of the Cenozoic.