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The cooling of the Southern Ocean around Antarctica, which began about 35 million years ago and gave rise to its current ice state, has been considered for decades as an example climate change, leading to rapid adaptation.
Using tens of thousands of genes mapped in the genomes of a group of Antarctic fish called notothenioids, a team of researchers is questioning this paradigm, revealing that the magnitude of the genetic change needed to life in Antarctica occurred well before the cooling of Antarctica. .
These genetic changes not only have major implications for understanding the evolution of unusual Antarctic animals, but they also highlight that some of the major adaptations used by fish reflect the genetics of the diseases of the Antarctic. human bones such as osteoporosis.
"Many species have developed traits that are adaptive in their environment but are similar to disease states in humans," said Jake Daane, lead author of the study (Northeastern University). "We use this natural variation to better understand the genetic mechanisms of the disease."
The team found evidence of an increase in the rate of mutation during the evolution of Antarctic fish prior to the onset of icy waters in the Southern Ocean, corresponding to a significant reduction in bone mineral density.
"Antarctic notothenioids do not have a swimbladder to adjust their buoyancy in the water column. Instead, they use reduced bone density to help them "float" in the low-energy water column, says co-author Bill Detrich (co-author). , Northeastern University). "What is a state of genetic disease in us is a means of survival for these fish."
"The genetic changes we have found are extremely pathological in humans, including those considered incompatible with life," said Alex Dornburg (co-author, North Carolina Museum of Natural Sciences). "Finding that notothenioids use the same genetic pathways to achieve buoyancy in water is a tremendous opportunity for human health research."
To test the function of the identified genetic modifications, the team also used advances in gene editing to design genetically modified zebrafish embryos bearing the same mutations as Antarctic notothenioids. As these zebrafish grew, they had the same bone loss as seen in Antarctic species.
"Our research shows that Antarctic notothenioids are important models of human disease.In addition to low bone density, Antarctic fish have also evolved into other apparently pathological conditions, including the loss of glomeruli and red blood cells. in the kidney, "said Matthew Harris. Boston Children's Hospital and Harvard Medical School).
Harris added, "These biomedically relevant processes can be investigated to reveal the genetic mechanisms underlying these disease states and their adaptation to these fishes, and the results should provide a better understanding of how to treat comparable disorders in humans." 39, man. "
Rather than changing these unusual adaptations in the face of major environmental upheavals, the team found that much of this genetic variation was already in place before the cooling of Antarctica. This finding challenges the way in which we view adaptation as opposed to permanent genetic diversity to predict the response of modern populations to contemporary climate change.
Antarctic notothenioids were at the right place at the right time to take advantage of the transition to an icy Antarctic there are millions of years. However, their future is uncertain.
"Notothenoids are of great ecological, economic and medical importance, but many species can not tolerate warming by more than a few degrees," said Thomas Near (co-author, Yale University). "Ironically, predictions of climate change now warn that this unique radiation of fish could be decimated over the next century and it is up to us to prevent such a tragic loss."
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The paper, "Historical contingency shapes adaptive radiation in Antarctic fish" was published as a pre-publication online on Nature Ecology & EvolutionThe website of June 10, 2019, and appears here: https: /
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