One would think that at least 184 million years of evolution on completely separate continents would be enough to make two species of fish sexually incompatible.
© Kaldy et al., Genes, 2020
That was the assumption of scientists in Hungary when they placed sperm from an American oarfish near the eggs of a Russian sturgeon in the laboratory.
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The idea was to get the endangered sturgeon eggs to reproduce asexually through a process called gynegenesis, which requires the presence of sperm without the introduction of any actual DNA.
The process clearly did not go as planned. It appears that the DNA was transferred after all, which inadvertently resulted in a new variety of fish known as the “big shot”.
These strange-looking creatures are a strange mixture of two very different-looking species, which could never have had contact if humans had not intervened.
Russian sturgeons feed along the soils of seas, lakes and rivers in Eastern Europe, Serbia and the Middle East. They are not found in the United States, even as an introduced species.
As the name implies, the American spoonbill can be found in the rivers of the United States, using its unusually long, paddle-shaped snouts to dig for food in the mud.
The descendants of these two species look, if possible, even stranger than their parents. Some resemble their mother and resemble their father, with classic sturgeon fins and snouts, along with typical oarfish mouths and appetites.
Others look much more like sturgeons than paddlefish.
“I did a double take when I saw it,” said aquatic ecologist Solomon David The New York Times.
“I just didn’t believe it. I thought, hybridization between sturgeon and oarfish? There’s no way.”
(Kaldy et al., Genes, 2020)
Above: The image above presents a typical Russian sturgeon; bottom image is of an American oarfish. The two images in the middle present hybrid examples of the two.
It may seem impossible, but as different as these fish look, they have remarkable similarities. Both species are known as living fossils, like crocodiles, because they have changed very little throughout their evolutionary history.
They both shared a common ancestor that lived during the age of dinosaurs, and while that might seem like a long time ago, for these fish that’s a drop in the bucket.
“These phenomena could lead to greater similarity, compatibility and flexibility between sturgeon genomes and allow hybridization between the Russian sturgeon and the American spoonbill fish despite the great geographical, physiological and morphological distances,” the authors argue.
That makes this a discovery, the team adds, as other hybridizations between equally distant taxonomic families have failed.
While these new fish are probably sterile, like other hybrids, they seem to survive at a similar rate to the American spoonbill. Some are still alive and swimming today.
Scientists have no plans to produce more of these hybrid fish, but will continue to study how sturgeon and paddlefish reproduce, in hopes of saving these fish from the brink of extinction.
Today, both fish families are in serious danger. Just this year, the Chinese spoonbill went extinct, and the International Union for Conservation of Nature reports that sturgeon are “critically endangered more than any other group of species.”
Hopefully they are on the right track.
The study was published in Genes.
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