The most important event in evolution took place millions of years ago. The genetic material of one of our closest fossil fish relatives is astonishing.
Konstanz – They are bizarre fish. “Evolution seems to have forgotten them” – writes an international team of researchers in a statement on a study published in the journal Nature published study. The genome of lungfish – especially the South American lungfish (Lepidosiren paradoxa) is gigantic. It is 30 times larger than that of humans. And thus the largest known genome of all animals.
The lungfish living today still look like their ancestors did 400 million years ago. All later land animals – the so-called four-legged animals (tetrapods) – can be traced back to living fossil fish. These include amphibians, reptiles, birds and mammals, including humans.
“They have changed life on our planet,” says the University of Würzburg’s press release announcing the study results. In order to further unravel the mystery of evolution, the genetic material of lungfish was sequenced. “The data will help us to understand how the ancestors of today’s land vertebrates managed to conquer the mainland.”
Secret of evolution: Largest animal genome to date sequenced
It was already known that the genomes of lungfish are enormous. However, the study led by evolutionary biologist Axel Meyer from Konstanz and biochemist Manfred Schartl from Würzburg shows how incredibly large they really are: The genome of the South American lungfish consists of more than 90 billion bases. It is therefore 30 times larger than the human genome and more than twice as large as that of the previous record holder, the Australian lungfish (Neoceratodus forsteri).
“18 of the 19 chromosomes of the South American lungfish are each larger than the entire human genome with its almost three billion bases,” said Axel Meyer, according to the statement from University of Würzburg.
Lungfish: Living fossils are relatives of our ancestors from around 420 million years ago
According to the researchers, today’s lungfish still look largely like their ancestors in the Devonian period. Thanks to their lungs, they were able to crawl out of the water and survive on land. Three lines of these ancient living fossils can still be found today in Africa, South America and Australia:
- South American lungfish (Lepidosiren paradoxa)
- Australian lungfish (Neoceratodus forsteri)
- African lungfish (Protopterus annectens)
Gigantic animal genome in lungfish – DNA sections “multiply”
The lungfish genome has grown over time through so-called autonomous transposons. “These are DNA sections that ‘multiply’ and then change their position in the genome – which in turn causes the genome to grow,” explains the research group. They make up more than 90 percent of the lungfish genome.
The expansion rate of the South American representative is by far the fastest known to date: every ten million years in the past, its genetic material has grown by the size of the entire human genome. “And it continues to grow,” reports Meyer. “We have found evidence that the responsible transposons are still active.”
Nevertheless, the genome of the lungfish is surprisingly stable. This is why the research team was able to reconstruct the original architecture of the chromosome set of the first four-legged creature (primitive tetrapod) from the sequences of the lungfish species still living today.
Devonian period
The Devonian period refers to a period in Earth’s history between about 420 and 360 million years ago.
The name Devon is derived from the British county of Devon(shire). It was chosen in 1839 by the British geologist Adam Sedgwick and Roderick Murchiso
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The flora and fauna during the Devonian period are characterized by a previously unprecedented biodiversity.
The Devonian period was the first time that vertebrates came onto land. For the first time in the history of the Earth, they were able to live outside of the water, at least temporarily.
Source: Spektrum.de/biologie-schule.de/Uni Würzburg
Fins are similar in bone structure to human arms and legs
According to the scientists, comparing the genomes of the various lungfish allows conclusions to be drawn about the genetic causes for the appearance of the lungfish living today. The Australian lungfish, for example, still has “limb-like” fins that its ancestors once used to move on land. In today’s lungfish representatives from Africa and South America, these fins, which are similar in bone structure to human arms and legs, have regressed into thread-like fins over the last 100 million years.
The team around Meyer and Schartl had already several years ago by analyzing the genetic material of the Australian lungfish shown that the same genes in humans and lungfish control the development of the lungs. The lungs of lungfish have the same evolutionary origin as those of land vertebrates, including humans. The animal’s fin also contains fingers, ulna and radius, for which the same genes are responsible as in humans. Scientists from Dresden, Hamburg, Sweden, Austria and France were also involved in the current study.
Our common ancestor is called LUCA (Last Universal Common Ancestor). In a study, researchers looked into the question of how life began on Earth.
In the A fascinating marine plant lives in the Baltic Sea. It is a real sensation. As an international team of researchers has now discovered.(ml)
#Mystery #fish #limblike #fins #solved
