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 notothenioid, 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.
“Many species have evolved traits that are adaptive in their environment but are similar to disease states in humans,” says Jake Daane, lead author of the study (Northeastern University).
“We use this natural variation to better understand genetic mechanisms
of disease.” 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.
“Antarctic notothenioids don’t have swim bladders to adjust their buoyancy in the water column. Rather, they use reductions in bone density to help them ‘float’ in the water column at low energetic cost,” says co-author Bill Detrich (coauthor, Northeastern University).
“What is a genetic disease state in us is a means of survival in these fishes.”
“The genetic changes we found are severely pathological in humans, including some that have been considered not compatible with life,” added Alex Dornburg (coauthor, North Carolina Museum of Natural Sciences).
“Finding that notothenioids use the same genetic pathways to achieve buoyancy in water represents a tremendous opportunity for human health research.”
To test the function of the genetic changes identified, the team further used advances in gene editing to engineer genetically modified zebrafish embryos with the same mutations as Antarctic notothenioids. As these zebrafish grew, they displayed the same loss of bone as observed in the Antarctic species.
“Our research is revealing Antarctic notothenioids to be important models for human disease. In addition to low bone density, Antarctic fishes also have evolved other apparently pathological conditions, including the
loss of kidney glomeruli and red blood cells,” says Matthew Harris (coauthor, Boston Children’s Hospital and Harvard Medical School).
Harris added, “These biomedically-relevant processes can be studied to reveal the genetic mechanisms behind these ‘disease’ states and their accommodation in these fishes. The results should lead to deeper understanding of how we might treat comparable disorders in humans.”