A bizarre new type of fish called a ‘sturddlefish’ that is a cross between a Russian sturgeon and American paddlefish has been created by scientists in a lab.
A team from the Research Institute for Fisheries and Aquaculture, Hungary, were trying to coax eggs from the endangered sturgeon into reproducing asexually.
Experts wanted to use a process called gynogenesis to find a way to make the sturgeon eggs fertilise themselves but this requires sperm to get it started.
They used American paddlefish sperm as it was thought the two species would be unable to reproduce due to the fact they have never come into contact with each other and the asexual process required the ‘sperm but not its DNA’.
However, despite living thousands of miles apart and their closest common ancestor dating back 184 million years, DNA from the paddlefish managed to fertilise the sturgeon eggs.
Researchers said the resulting fish, like many hybrid species, are infertile and they have no plans to produce anymore – but the survivors could live over 100 years.
Two examples of the ‘offspring’ of the Russian Sturgeon and American Paddlefish. Some of the surviving offspring tooked more like sturgeon and others like paddlefish
Russian sturgeons feed on the floor of seas, lakes and rivers in eastern Europe, Siberia and the Middle East but aren’t found in the US at all.
In contrast the American paddlefish are found in the rivers of the US and not in eastern Europe, Siberia and the Middle East. The two have never mixed.
Despite this, a new species of sturddlefish – from a female sturgeon and male paddlefish – has been created in a lab ‘accidentally’ despite researchers predicting it would be impossible for the two to produce offspring.
The team say this could be due to the fact they are both ‘living fossil’ species, that is that they have changed very little since their last common ancestor was alive.
‘These phenomena could lead to a higher similarity, compatibility, and flexibility among the sturgeon genomes,’ the authors wrote in their paper published in Genes.
Adding that it could ‘allow the hybridisation between Russian sturgeon and American paddlefish despite the large geographical, physiological, and morphological distances.’
This is a significant discovery as other ‘blending’ of distant species from similar families to these two have failed to reproduce.
Researchers say their offspring look even weirder than their parent species – with some half-resembling their mother, half their father and some like both.
Some bear classic sturgeon fins and snouts with the typical paddlefish mouth.
‘I did a double-take when I saw it,’ aquatic ecologist Solomon David told The New York Times.
‘I just didn’t believe it. I thought, hybridisation between sturgeon and paddlefish? There’s no way.’
Sturgeons and paddlefish do share some things in common. They are among the largest, longest -living and slowest-growing freshwater fish species
They are also both critically endangered due to habitat loss, overfishing and pollution taking their toll on both species over the last century.
Attila Mozsar and colleagues in Hungary were trying to find a way to breed both fish in captivity by inducing gynogenesis – a form of asexual reproduction.
This works by requiring the presence of sperm to trick the egg into fertilising itself but only works if there is no compatible DNA contained in the sperm.
Top is a typical American Paddlefish and bottom is an image of a typical Russian sturgeon like the ones used to produce the sturddlefish
‘We never wanted to play around with hybridization. It was absolutely unintentional,’ said Dr. Mozsár.
The unexpected fertilisation resulted in hundreds of hybrid fish emerging from the eggs, and the team say two-thirds of them survived.
This suggests the two species are more alike than previously thought – despite never having mixed and being separated by thousands of miles of ocean.
This is likely due to the extremely slow evolutionary rate of the fish species – so while they evolved independently, they hold many features of their last common ancestor that existed during the time of the dinosaurs 184 million years ago.
The team say the fish were likely sterile and so wouldn’t not be able to go on to further reproduce and they had no plans to create any more of the hybrid species.
They said they’d continue to study the way sturgeon and paddlefish and the way they reproduce in the hope of saving them from the brink of extinction.
Both fish are listed as seriously endangered with the Chinese paddlefish going extinct earlier this year and sturgeon ‘more endangered than any other group’.
The study was published in the journal Genes.
GYNOGENESIS: COAXING EGGS TO REPRODUCE WITHOUT THE NEED FOR MALE DNA
Gynogenesis is a method for producing fish without the need for male DNA – all the genetic information originated from the female parent.
It is a form of parthenogenesis and is a system of asexual reproduction – but unlike other forms of asexual processes – it does require a sperm.
One method, used in salmon, is to fertilise the egg using irradiated sperm that removes all of its genetic material – it is there to ‘trick the egg’.
Ideally the sperm is taken from a related species that does not produce viable offspring through fertilisation under normal circumstances.
The paternal DNA is destroyed before it can fuse with the egg but is enough to get the egg to develop, unfertilised into an adult only using its mothers DNA.
Another name for the process is sperm parasitism – referring to the ‘pointless role of male genes’ in the production of fish – why this process of a mix of asexual and sexual reproduction evolved is unknown.