By Kate Golembiewski, May 31, 2022
In Shark Bay, off the westernmost tip of Australia, meadows of sea grass carpet the ocean floor, undulating in the current and being nibbled on by dugongs, cousins of Florida manatees. A new study revealed something unexpected about those sea grasses: Many of them are the same individual plant that has been cloning itself for about 4,500 years.
The sea grass — not to be confused with seaweed, which is an algae — is Poseidon’s ribbon weed, or Posidonia australis. Jane Edgeloe, a University of Western Australia Ph.D. candidate and an author of the paper, likens its appearance to a spring onion.
Ms. Edgeloe and her colleagues made their discovery as part of a genetic survey of Posidonia grasses in different areas of Shark Bay, where she SCUBA dived in the shallow waters and pulled up shoots ofPosidonia from 10 different meadows. On land, the researchers analyzed and compared the grasses’ DNA.
They published their results Wednesday in the journal Proceedings of the Royal Society B. It turned out the DNA of many of those seemingly different plants was virtually identical. Elizabeth Sinclair, also of the University of Western Australia and an author of the study, recalled excitement in the lab when she realized: “It’s only one plant.”
While some of Shark Bay’s northern meadows reproduce sexually, the rest of its Posidonia clones itself by creating new shoots that branch off from its root system. Even separate meadows were genetically identical, indicating that they were once connected by now-severed roots. Based on how old the bay is and how quickly sea grasses grow, the researchers surmise that the Shark Bay clone is about 4,500 years old.
In addition to being a clone, the grass seems to be a hybrid of two species and possesses two complete sets of chromosomes, a condition called polyploidy. While polyploidy can be lethal for animal embryos, it can be harmless or even helpful in plants. However, it can result in sterility: Much of the clonal grass does not flower and can only reproduce by continuing to clone itself.
This combination of extra genes and cloning might have been the key to the grass’s survival during a period of ancient climate change: Cloning made reproduction easier because the grass did not have to bother finding a mate. The extra genes could have given the sea grass “the ability to cope with a broad range of conditions, which is a great thing in climate change,” Dr. Sinclair said.
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