Antifreeze proteins in the bodily fluids of Antarctic fishes are a crucial adaptation to life in the freezing waters — but their appearance alone is insufficient to explain the huge diversity of the region's fish species. Thomas Near of Yale University in New Haven, Connecticut, and his colleagues constructed a phylogeny of these notothenioid fishes (a sample pictured) and correlated it to both the appearance of the proteins and changes in global climate.

Credit: T. J. NEAR

Contrary to the perception that the appearance of antifreeze proteins was the crucial factor driving evolution, they found that the most species-rich lineages diversified at least 10 million years after the proteins' appearance. This bout of evolution happened during a second cooling event in the Late Miocene (11.6 million to 5.3 million years ago), when ice activity in the Southern Ocean is thought to have increased. The authors suggest that the appearance of this new polar habitat, combined with the pre-existing antifreeze proteins, spurred the evolution of notothenioids.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1115169109 (2012)