Evolution of Type II Antifreeze Protein Genes in Teleost Fish: A Complex Scenario Involving Lateral Gene Transfers and Episodic Directional Selection

I examined hypotheses about lateral transfer of type II antifreeze protein (AFP) genes among "distantly" related teleost fish. The effects of episodic directional selection on amino acid evolution were also investigated. The strict consensus results showed that the type II AFP and type II antifreeze-like protein genes were transferred from Osmerus mordax to Clupea harengus, from the ancestral lineage of the Brachyopsis rostratus-Hemitripterus americanus clade to the ancestor of the Hypomesus nipponensis-Osmerus mordax group and from the ancestral lineage of Brachyopsis rostratus-Hemitripterus americanus-Siniperca chuatsi-Perca flavescens to Perca flavescens. At the present time, the available evidence is more consistent with the LGT hypothesis than with other alternative explanations. The overall results indicate that evolutionary history of the type II AFP gene is complex, and that episodic directional selection was instrumental in the evolution of this freeze-preventing protein from a C-type lectin precursor.