At first glance, the American spoonbill and the Russian sturgeon look as different as two fish can be.
The Russian sturgeon, whose eggs are used to make premium caviar, is a carnivore that hovers crustaceans and smaller fish from the soil of rivers, lakes and coastal areas around the world. Found in only 22 in the United States, the American spoonbill is a filter feeder that filters zooplankton from water. It has a comically long muzzle covered with tens of thousands of sensory receptors.
However, somehow, when the sperm of an American spoonbill and the eggs of a Russian sturgeon were combined in a laboratory, life found a way and a hybrid of the two species was born.
“I did a double take when I saw it,” said Solomon David, an aquatic ecologist at Nicholls State University in Louisiana. “I just didn’t believe it. I thought, hybridization between sturgeon and oarfish? There is no way.”
Hungarian researchers who accidentally created this hybrid reported what they had done in May in a study published in the journal Genes. The internet has already nicknamed the hybrid the big shot. The Hungarian team’s research highlights how creatures that appear distant on the tree of life may be sitting on branches closer than expected.
Sturgeons and paddlefish are among the largest, longest-lived, and slowest-growing freshwater fish on Earth. They are also among the most threatened. The paddlefish is the only species that continues to exist after a Chinese species was declared extinct, and the sturgeon is “critically endangered more than any other group of species,” according to the International Union for Conservation of Nature.
Habitat loss, overfishing and pollution have had a high cost on paddlefish and sturgeon for the past century, which is why Attila Mozsár, principal investigator at the Hungarian Fisheries and Aquaculture Research Institute and co-author of the study , and others have been trying to breed both fish in captivity.
Last year, researchers tried to induce gynegenesis, a form of asexual production that requires the presence of sperm, but not the actual contribution of its DNA, in the Russian sturgeon.
Something unexpected happened: the oarfish sperm that the researchers were using successfully fertilized sturgeon eggs.
“We never wanted to play with hybridization. It was absolutely involuntary, ”said Dr. Mozsár.
Hundreds of hybrids emerged from those eggs, and a month later, more than two-thirds of them were still alive. Around 100 of these hybrids are alive today.
Both creatures are known as “fossil fish” due to their ancient lineage. Their last common ancestor swam during the age of dinosaurs, and the two have been evolving independently, on opposite sides of the planet, for more than 184 million years, making them almost twice as evolutionarily divergent as humans and mice. . That led scientists to suppose that they were evolutionarily too divergent to be hybridized.
The sturddlefish created in Hungary exhibited traits of both species. Although they all have their mother’s carnivorous mouth and appetite, some have their father’s snouts and fins, albeit a little smaller. After conducting DNA analysis on eight sturddlefish, the researchers were able to separate the hybrids into two groups. Some of the sturddlefish got a double dose of DNA from their mother, and they look much more like sturgeon than paddlefish. The others received almost equal amounts of maternal and paternal DNA, and appear to be a perfect combination of the two species.
Russian sturgeon and American swordfish may not seem like they have much in common, but the fact that they can hybridize suggests that they may be more alike than previously thought.
“Many aspects of their anatomy and physiology are really very similar,” said Dennis Scarnecchia, professor of fishery resources at the University of Idaho. Both species have scaleless skin, spiral valvular intestines, and cartilaginous endoskeletons.
Although it seems unlikely that two species have so much in common after spending centuries evolving independently, 184 million years is not really that long for these fish.
“These living fossil fish have extremely slow evolutionary rates, so what might seem like a long time is not that long to them,” said Dr. David.
Although Dr. Mozsár and his colleagues plan to continue caring for the hybrids they created, they have no plans to do more. Researchers suspect that sturddlefish, such as ligers, mules, and many other man-made hybrids, are sterile, making them of no value for caviar production. Creating more sturddle fish could also endanger wild fish stocks.
However, the sturddlefish has captured the imaginations of scientists around the world.
“I think it’s great that these living fossils can still surprise us,” said Dr. David.
