The cooling of the Southern Ocean surrounding Antarctica, which began approximately 35 million years ago and gave rise to its present icy state, has for decades been considered a classic example of climate change triggering rapid adaptation. Using tens of thousands of genes mapped from across the genomes of a group of Antarctic fishes called notothenioids, a team of researchers is now challenging this paradigm, revealing that the massive amount of genetic change required for life in the Antarctic occurred long before the Antarctic cooled. These genetic changes not only have major implications for understanding the evolution of Antarctica's unusual animals, but also highlight that some key adaptations used by fishes mirror the genetics of human bone diseases such as osteoporosis. The team found evidence of an increase in mutation rate during the evolution of Antarctic fishes prior to the onset of icy waters in the Southern Ocean that corresponded with a severe reduction of bone mineral density. These findings challenge how we consider adaptation versus standing genetic diversity to predict the response of modern populations to contemporary climate change.
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