Molecular origins and mechanisms of fish antifreeze evolution

Independent evolution of distinctive types of antifreeze glycoprotein (AFGP) and peptides (AFP) in various polar and subpolar bony fish lineages bespeaks the breath of evolutionary ingenuity in converging on a similar life-preserving solution under extreme selective pressures from lethal, icy freezing marine conditions. Fish AF(G)Ps represent clear examples of a single adaptive genotype conferring a crucial fitness phenotype in a clear causal manner, which are exceptionally rare in evolutionary biology. Studies of the antifreeze function have richly enhanced our understanding of this new form of biochemical and physiological adaptation to extreme cold in marine vertebrate ectotherm. Additionally, the diverse AF(G)P genotypes are genetic novelties, and studies of their evolution have richly informed the field of molecular evolution on the array of innovative processes by which new genes arose, from classical evolution through gene duplication, to creating protein-coding gene from entirely noncoding DNA. This chapter reviews the origins and molecular mechanisms of fish AF(G)P genes that have been deduced in the past three decades and outstanding uncertainties, narrated as a historical account, with relevant environmental, organismal, physiological, and evolutionary considerations.