How it happened
The initial goal of the study was to encourage the critically endangered sturgeon to reproduce asexually. That isn’t quite how it went.
The Russian sturgeon, instead, hybridized with the American paddlefish, the first time the two have ever hybridized successfully in captivity. The paddlefish was originally meant to provide sperm — not its DNA — to help the sturgeon reproduce on its own.
The sturgeon isn’t so genetically different from paddlefish — they belong to the same group, Acipenseriformes. According to the US Fish and Wildlife Service
, sturgeon and paddlefish both provide tasty caviar.
But they weren’t supposed to hybridize. Previous hybridization attempts between American paddlefish and other sturgeons hadn’t worked, the authors wrote. And for their evolutionary similarities, the two have vastly different feeding habits, preferred habitats and physical characteristics.
Plus, the two fish would never have met naturally. The American paddlefish dwells in the Mississippi River Basin, and the Russian sturgeon inhabits Russian rivers. The Russian sturgeon is considered extremely valuable for its roe, or eggs. Both species are threatened by shrinking habitats and overfishing.
While the caviar that comes from sturgeons is a delicacy, the fish themselves are exceedingly rare in Russian waters. That’s why the researchers, all from Hungary, wanted to encourage the sturgeon to reproduce through gynogenesis, which uses the treated sperm of another species to coax the specimen’s eggs to develop.
But in gynogenesis, the DNA of the sperm specimen isn’t supposed to transfer to the offspring.
What the hybrids could do next
There were two types of hybrid fish: One of them is one part paddlefish, two parts sturgeon, and the other is one part paddlefish, four parts sturgeon. Most of them, between 62% to 74%, survived one month after hatching.
Both hybrids resembled the sturgeon, with its ridged back and short nose, though one of them did have a pointier snout reminiscent of its paddlefish parent.
“The how and why are still open questions,” said lead author Jenő Káldy, an aquaculture researcher at Hungary’s National Agricultural Research and Innovation Centre’s Research Institute for Fisheries and Aquaculture. The two likely hybridized because the sturgeon was slow to evolve. This means there are likely fewer differences between its morphology and genes and those of other species, including, apparently, the American paddlefish.