Disaptation and recovery in the evolution of Antarctic fishes.

The radiation of notothenioid fishes provides an excellent system to explore issues of evolution and adaptation. Most studies emphasize adaptation to the extreme Antarctic environment; however, recent work provides cogent examples of disaptation or evolutionary loss of function. The nature and extent of regressive change is revealed by subsequent adaptive recovery. Ancestral notothenioids were benthic but some became secondarily pelagic through the retention of larval characters. Paedomorphosis has produced detrimental changes in lateral-line sensory systems that have been made good by compensatory adaptation. In the icefish family, compensatory adaptation has followed the loss of the oxygen-binding pigments haemoglobin and myoglobin.