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A study of octopus DNA may have solved a lasting mystery about when the rapidly melting West Antarctica ice sheet last collapsed, unlocking valuable information about how much future sea levels might rise in a warming climate.
The innovative research focused on the genetic history of the Turquet octopus (Pareledone turqueti), which lives on the Antarctic seabed, and what it could reveal about the region’s geology over time.
Tracing past encounters between the species’ different populations suggested that the most recent ice sheet collapse occurred more than 100,000 years ago during a period known as the Last Interglacial — something geoscientists suspected but had not been able to definitively confirm, according to the published study. Thursday in the journal Science.
“This project was exciting because it offers a brand new perspective to solve a long-standing question in the geoscience community,” said lead study author Sally Lau, a postdoctoral researcher at James Cook University in Australia.
“The DNA of living animals today contains all the information about their past ancestors, so it’s like a time capsule,” she said.
The research team made its findings by sequencing the DNA of 96 Turquet octopuses collected by institutions around the world and by fishing bycatch over the years. The oldest samples dated from the 1990s, but when sequenced their genes provided a detailed family tree stretching back millions of years.
The family tree of octopuses
The DNA analysis allowed researchers to understand whether different populations of Turquet octopuses had interbred and at what point that interbreeding had occurred.
“It’s like doing a 23andMe on the octopus,” Lau said, referring to the genetic testing company. “This information is passed on from parents to children and grandchildren, and so on.”
Today, populations of Turquet octopus in the Weddell, Amundsen and Ross seas are separated by the continent-sized West Antarctic ice shelves and cannot intermingle.
However, the study suggested that genetic connectivity between these populations last occurred about 125,000 years ago, during the last interglacial, when global temperatures were similar to today.
This finding indicated that the West Antarctic Ice Sheet had collapsed during this period – an event that would have flooded coastal areas, but opened up ice-bound areas on the seafloor for the octopuses to occupy, eventually encountering members of the Turquet populations and could reproduce with it. that were once geographically separated.
“What makes the WAIS important is that it is also Antarctica’s current largest contribution to global sea level rise. A complete collapse could raise global sea levels by somewhere between 3 and 5 meters,” study author Jan Strugnell, professor and director of the Center for Sustainable Tropical Fisheries and Aquaculture at James Cook University, said in a statement. Strugnell first came up with the idea of using genomic methods to investigate whether the ice sheet collapsed during the last interglacial.
“Understanding how the WAIS was configured in the recent past when global temperatures were similar to today can help us improve future sea level rise projections,” she said.
Why octopuses?
The team chose this octopus species for the study because the animals are relatively immobile: they can only crawl on the seabed, meaning they are more likely to reproduce within their genetically distinct local populations. In contrast, a fast-moving marine species like krill would have more homogeneous DNA, blurring historical genetic connections, Lau said.
Furthermore, the biology of the Turquet octopus is relatively well studied and scientists understand its DNA mutation rate and generation time, which are crucial for accurate molecular dating, Lau added.
Previous studies involving species of crustaceans and marine molluscs had discovered a biological signature of ice shelf collapse with direct connections between the Ross and Weddell seas, Lau noted. But the new Turquet octopus study was the first with enough high-resolution data and an adequate sample size to understand whether that genetic connectivity was caused by the collapse of the ice sheet or by a much more gradual movement of octopuses along its edges.
Lau said her team’s genetic approach could not reveal exactly when the ice sheet collapsed or how long that event lasted. However, with fresh octopus samples and more advanced DNA analysis techniques, it may be possible to resolve these questions in the future.
“We would like to continue using DNA as a proxy to explore other parts of Antarctica where climate history is poorly understood,” she said. “We are constantly looking for new species to test these scientific questions.”
‘Groundbreaking’ study
In a commentary published alongside the study, Andrea Dutton, a professor in the department of geosciences at the University of Wisconsin-Madison, and Robert M.
DeConto, a professor at the University of Massachusetts Amherst’s School of Earth and Sustainability, called the new research “groundbreaking.”
They noted that while geological evidence had been accumulating that the icy expanse of the West Antarctic Ice Sheet may have collapsed during the last interglacial period, “the findings of each study come with caveats.”
Deploying a completely different data set for this pressing issue “posed a number of intriguing questions, including whether this history will repeat itself given Earth’s current temperature trajectory,” she added.
Using octopus genomics was “an innovative and exciting way” to tackle an important question about historical climate change, says Douglas Crawford, a professor of marine biology and ecology at the University of Miami, who was not involved in the study.
“This is a careful study with sufficient sample size and a carefully vetted set of genetic markers,” he added.
“It takes a challenging hypothesis and uses a completely independent data set that (ultimately) supports that WAIS has collapsed,” he said via email.
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