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A study of octopus DNA may have solved an enduring mystery of when the fast-melting West Antarctic ice sheet last collapsed, leaving behind valuable information about how much sea levels may rise in the future in climate heating.
The innovative research focused on the genetic history of the Turquet octopus (Pareledone turqueti), which lives on the seabed across the Antarctic, and what it could reveal about the region’s geology over time.
Looking for past contacts of the different populations of the species revealed that the most recent ice sheet collapsed more than 100,000 years ago during a period known as the Last Interglacial – something geologists suspected but that they were not able to confirm definitively, according to the published study. Thursday in the journal Science.
“This project was exciting because it brings a fresh perspective to solving a long-standing question in the geoscience community,” said lead study author Sally Lau, a postdoctoral research fellow at James Cook University in Australia.
“The DNA of animals alive today contains all the information about their ancestors (in) the past, so it’s like a time capsule,” she said.
The research team reached 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 date back to the 1990s, but when sequenced, their genes provided a detailed family tree that essentially went back millions of years.
Octopus family tree
The DNA analysis enabled researchers to understand whether different populations of Turquet’s octopus had interbred and at what point that interbreeding occurred.
“It’s like doing 23andMe on the octopus,” Lau said, referring to the genetic testing company. “This knowledge is passed on from parents to children and grandchildren and so on.”
Today, Turquet octopus populations in the Weddell, Amundsen and Ross Seas are separated by the large West Antarctic ice shelves and cannot interbreed.
However, the study suggested that the last genetic connection between these populations was around 125,000 years ago, during the Last Interglacial, when global temperatures were similar to today’s.
This finding indicated that the West Antarctic ice sheet had collapsed during this time — an event that would have flooded the coastal regions but opened up glaciated areas on the sea floor that the octopuses would have been able to inhabit, turning and eventually breeding with members of the Turquet population. which were once geographically separated from each other.
“What makes the WAIS important is that Antarctica is the biggest contributor to global sea level rise. A total drop in global sea levels could raise somewhere between 3 and 5 meters,” study author Jan Strugnell, professor and director of the Center for Tropical Fisheries and Sustainable Aquaculture at James Cook University, said in a statement. Strugnell first came up with the idea of using genomic methods to investigate the collapse of the ice sheet during the Last Interglacial.
“Understanding how WAIS was configured recently when global temperatures were similar to today will help us improve future sea level rise projections,” she said.
Why octopus?
The team chose this species of octopus for the study because the animals are relatively immobile – they can only crawl along the seabed, meaning they are more likely to breed within their genetically distinct local populations. In contrast, a fast-moving marine species such as krill would have more homogeneous DNA, blurring historical genetic links, Lau said.
In addition, the biology of the Turquet octopus has been relatively well studied, and scientists understand its DNA mutation rate and generation time, which is critical for accurate molecular dating, Lau said.
Previous studies involving crustacean and marine mollusc species have identified a biological signature of ice shelf collapse with a direct link between the Ross and Weddell seas, Lau noted. But Turquet’s new octopus study was the first with enough high-resolution data and a sufficient sample size to understand whether that genetic connectivity was driven by the collapse of the ice sheet or the gradual movement of much larger octopuses around on its edges.
Lau said her team’s genetic approach could not reveal exactly when the ice sheet collapsed or how long that event took. However, with fresh octopus samples and more advanced DNA analysis techniques, these questions may be resolved in the future.
“We’d love to continue using DNA as a proxy to explore other parts of Antarctica that don’t have a well-understood climate history,” she said. “We are always looking for new species to test these scientific questions.”
A ‘groundbreaking’ study
In a commentary published alongside the study, Andrea Dutton, a professor in the Department of Geology at the University of Wisconsin-Madison, and Robert M.
DeConto, a professor in the School of Earth and Sustainability at the University of Massachusetts Amherst, called the new research “groundbreaking.”
They noted that while there was growing geological evidence that the glacial extent of the West Antarctic ice sheet may have declined during the Last Interglacial period, “the results of each study have come with a caveat.”
They asked some interesting questions, including whether this history will repeat itself, given the Earth’s current temperature trajectory, when they brought a completely different set of data to this pressing issue.
Using the octopus genome was an “innovative and exciting way” to address an important question about historical climate change, said Douglas Crawford, a professor of marine biology and ecology at the University of Miami who was not involved in the research.
“This is a careful study with a sufficient sample and a set of genetic markers that have been vetted,” he said.
“It takes a challenging hypothesis and uses a completely independent data set that (finally) supports the WAIS collapse,” he said via email.
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