Studying how fish living in the world's coldest environment adapted to nascent polar conditions millions of years ago is the subject of a paper to be published in a forthcoming issue of the Proceedings of the National Academy of Sciences.
The suborder Notothenioidei is a group of more than 100 species found exclusively in Antarctic waters.
Accounting for the bulk of fish diversity around Antarctica, they possess antifreeze glycoproteins that allows them to survive in frigid waters, and are an important food source for larger predators.
The authors used a time-calibrated molecular phylogeny of notothenioids and reconstructed palaeoclimate to show that the antifreeze glycoproteins evolved sometime around 42 to 22 million years ago, coinciding with a period of global cooling around 35 million years ago.
However, the most species-rich lineages radiated at least 10 million years after the evolution of antifreeze glycoproteins, indicating that the acquisition of the glycoproteins was not the sole factor for the notothenioids’ success.
The authors surmise that the combination of glycoprotein acquisition, as well as the exploitation of new ecological niches and habitats brought about by increased glacial and ice sheet activity during a second period of global cooling about 12–5 million years ago, led to the diversification of the lineage.
In a tragic twist of fate, the notothenioids are so well-adapted to polar conditions that they are now threatened by global warming, with a rise as little as 2°C being enough to devastate this unique lineage, according to lead author Thomas Near.
"Given their strong polar adaptations and their inability to acclimate to warmer water temperatures, climate change could devastate this most interesting lineage of fish with a unique evolutionary history," Near said.
For more information, see the paper: Near, TJ, A Dornburg, KL Kuhn, JT Eastman, JN Pennington, T Patarnello, L Zane, DA Fernández, and CD Jones (2012) Ancient climate change, antifreeze, and the evolutionary diversification of Antarctic fishes. Proceedings of the National Academy of Sciences of the United States of America doi:10.1073/pnas.1115169109
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