The sturddlefish has a mix of genes from the Russian sturgeon and the American spoonbill. (Credit: Genes 2020, 11 (7), 753; https://doi.org/10.3390/genes11070753, CC BY 4.0)
It shouldn’t have been possible, but it was: the birth of long-nosed, pointy-finned hybrids of Russian sturgeons and American spoonbills.
Hungarian scientists announced in the magazine Genes in May that they had accidentally created a hybrid of the two endangered species, which they called the “big shot.” There are around 100 of the hybrids in captivity now, but the scientists have no plans to create more.
“We never wanted to play with hybridization. It was absolutely unintended,” Attila Mozsár, principal investigator at the Hungarian Fisheries and Aquaculture Research Institute, told The New York Times.
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Russian sturgeons (Acipenser gueldenstaedtii) are critically endangered and also economically important: they are the source of much of the world’s caviar. These fish can grow to more than 7 feet long (2.1 meters), living on a diet of mollusks and crustaceans. The American spoonbill fish (Polyodon spathula) feeds on zooplankton in the waters of the Mississippi River drainage basin, where the Mississippi water and its tributaries flow into. They are also large and grow up to 8.5 feet (2.5 m) long. Like sturgeon, they have a slow rate of growth and development that puts them at risk of overfishing. They have also lost habitat to dams in the Mississippi drainage, according to the University of Michigan Museum of Zoology. The two species last shared a common ancestor 184 million years ago, according to the Times.
However, they were able to reproduce, to the surprise of Mozsár and his colleagues. The researchers were trying to breed the Russian sturgeon in captivity through a process called gynegenesis, a type of asexual reproduction. In gynegenesis, a sperm triggers the development of an egg but does not fuse with the nucleus of the egg. That means that their DNA is not part of the resulting offspring, which grows only from maternal DNA. Investigators were using American spatula fish sperm for the process, but something unexpected happened. The sperm and ovum fused together, resulting in offspring with sturgeon and paddlefish genes.
The resulting revolver fish hatched by the hundreds, and around 100 now survive, according to the Times. Some are only around 50-50 sturgeon and paddlefish gene mixtures, and some are much more similar to sturgeon. They are all carnivores, like the sturgeon, and share the sturgeon’s more forceful nose, compared to the pointed snout of the oarfish.
Most hybrid species, such as liger (a mix of a lion and a tiger) and a mule (a mix of a horse and a donkey), cannot have offspring of their own, and the big shot is probably no exception. Mozsár and his colleagues plan to take care of the fish, but they will not create more, since the hybrid could compete with the native sturgeon in the wild and worsen the sturgeon’s survival chances.
However, the fact that fish separated by 184 million years of evolution can interbreed indicates that they are not so different, after all.
“These live fossil fish have extremely slow evolutionary rates, so what might seem like a long time to us is not that long for them,” Solomon David, an aquatic ecologist at Nicholls State University in Louisiana, told the Times. .
Originally published in Live Science.
