Most crayfish reproduce by having sex.
But an all-female species of mutant crayfish has managed to evolve the ability to clone itself, without the need for a male.
Known as marmokrebs, or marbled crayfish, the species’ remarkable cloning ability has led it to multiply out of control.
Now scientists are warning the female crustaceans are beginning to take over Europe and parts of Africa because they are reproducing so quickly.
While it may sound like the plot of the horror movie, they say there may be some benefits to the strange crayfish invasion; the crayfish’s unusual evolution could also provide a strategy to tackle cancer as it clones itself in a similar way. Most crayfish reproduce by having sex. But an all-female species of mutant crayfish, known as marble crayfish (pictured) has managed to evolve the ability to clone itself, without the need for a male
Since being found in 1995, the marbled crayfish has spread from Germany across Europe and into Africa in huge numbers.
‘This crayfish is a serious pest,’ Gerhard Scholtz, an evolutionary biologist at Humboldt University in Berlin, who has tracked its rapid spread across the globe, told Science Magazine.
The European Union has now banned the species, and says it must not be sold, kept, distributed, or released to the wild.
In a new study published in the journal Nature Ecology and Evolution, researchers sequenced the genomes of the 11 marbled crayfish to see how they spread so rapidly.
All 11 creatures had nearly identical genomes, suggesting they were clones.
Researchers believe these mutant creatures began evolving by accident almost 25 years ago, after a German aquarium hobbyist bought a crayfish that he was told was a ‘Texas crayfish’.
But he was surprised when his marbled crayfish produced hundreds of eggs at a time and grew large.
He gave away the crayfish, and they eventually ended up being sold in pet shops in Germany.
But owners soon began noticing that their Marmokrebs were reproducing without the need to mate, and all offspring were female, fertile and clones of their mother.
Once the new species of crayfish evolved, male slough crayfish could no longer produce offspring with the female Marmokrebs, even though the male slough fish could still physically mate with the Marmokrebs. Known as marmokrebs, or marbled crayfish, the species’ remarkable cloning ability has led it to ‘multiply out of control’. Now scientists are warning the female crustaceans are beginning to take over the world
The Marmokrebs reproduced rapidly, and as owners began dumping them in rivers and lakes, they spread through Europe, as well as Japan and Madagascar.
Currently, no one knows exactly how many crayfish are spreading around the world, but they believe the number is significant and rapidly growing.
‘Here we have an evolutionary event that has happened only a very short time ago,’ Frank Lyko, Head of divisions of epigenetics at the German Cancer Research Center told Newsweek.
HOW DOES CLONING HAPPEN IN NATURE?
Asexual reproduction – when an organism reproduces without fertilisation – only requires one parent, unlike sexual reproduction, which needs two parents.
Since there is only one parent, sec cells (sperm and eggs) don’t fuse and no genetic mixing takes place.
Because of this, the offspring of asexual reproducing organisms are genetically identical to the parent and to each other – they are clones.
For instance, female marble crayfish can induce her own eggs to start dividing into embryo .
Normal sex cells contain a single copy of each chromosome. But the mutant crayfish sex cell has two.
The two sex cells fuse and produce a female crayfish embryo with three copies of each chromosome instead of the normal two.
Some other examples of organisms that can clone themselves include:
‘Certainly there will be some changes, genetic changes over time, that will make it more normal. At this specific time point in evolution it’s very unique.’
In their new study, researchers from the German Cancer Research Center in Heidelberg, Germany provided proof that the all-female offspring of the Marmokrebs are genetically identical.
‘We could detect only a few hundred variants in a genome that is larger than the human genome,’ said Dr Frank Lyko, the lead author of the research.
‘That is an incredibly small number.
‘The minute variations can be ascribed to natural mutations.’
The researchers also examined how well the crayfish are able to spread via asexual reproduction, and its reproductive success came as a surprise to the researchers. Distribution of marbled crayfish on Madagascar (as of March 2017). Red dots indicate discovery sites where the presence of marbled crayfish was confirmed by DNA sequencing. White dots indicate sites where no marbled crayfish were found
‘It was known that the crayfish can establish itself in the wild after releases from the aquarium,’ Dr Lyko said.
‘But the news was that it can spread so rapidly and massively.’
Aside from subtropical Madagascar, Marmokrebs also occur in Sweden, Japan, Freiburg, Hanover and Heidelberg highlighting the species’ remarkable adaptability without sexual reproduction
This was surprising to the researchers because it is widely known and accepted that sexual reproduction, and the resulting mix of paternal and maternal gens that enlarge genetic variety, facilitate rapid adaptation to adverse environmental conditions.
Although Marmokrebs are all clones born with the same genes, they can adapt to a wide variety of environments via epigenetic mechanisms, regulated by small chemical tags attached to DNA.
These epigenetic mechanisms regulate how genetic information is interpreted, and they work like switches that turn genes on or off.
According to the researchers, it is this epigenetic regulation could make Marmokrebs interesting for tumor researchers.
Scientists have known for a couple of years that epigenetic mechanisms also play a key role in these processes, and can influence cancer risk and the disease course.
A phenomenon called clonal evolution occurs both in Marmorkrebs and in tumors.
‘Tumor genomes also evolve clonally, because they go back to a single original cell,’ said Dr Lyko.
The research team now wants to use marbled crayfish to further investigate their role.Marbled crayfish by-catch in a traditional fishing tool or ‘tandroho’. Although Marmokrebs are all clones born with the same genes, they can adapt to a wide variety of environments via epigenetic mechanisms, regulated by small chemical tags attached to DNA