A species of crayfish is able to clone itself, producing biologically fertile offspring just from the eggs of the mother crayfish. The crayfish has spread out from its initial habitat and is taking over large portions of the globe thanks to its aggressive nature and ability to replicate itself quickly.
During 1995 the owner of a German aquarium discovered that all the crayfish in his tank were biologically the same. They used a process known as parthenogenesis to lay eggs which hatch without needing to be fertilized. The creature was dubbed the marbled crayfish by scientists.
An Invasive, Self-replicating Clone
Due to the species’ ability to self-replicate and its aggressive nature, the species has become a problematic invasive species that has spread across much of the globe. In addition to Germany, it can now be found in Italy, Slovakia, Japan, Madagascar, and Sweden.
Scientists have recently just sequenced the DNA of the crayfish, using eleven different specimens. One specimen was taken from the original German petshop and at least one was caught wild in Madagascar. The genetic tests prove that the crayfish are clones of one another, with astonishingly little genetic diversity. Frank Lyko, an epigenetics researcher who led the study, says that the crayfish have three different sets of chromosomes. This makes them triploid animals. Most animals are diploid, inheriting one set of chromosomes from their mother and one from their father. It’s possible, though not conclusive, that the three sets of chromosomes may play a role in the Crayfish’s ability to self-replicate.
Says Lyko:
People would start out with a single animal, and a year later they would have a couple hundred.
The crayfish is said to have escaped into the environment when owners of the crayfish would drive to nearby lakes and dump the crayfish in.
“They eat anything—rotten leaves, snails or fish broods, small fish, small insects,” says Frank Lyko about the marbled crayfish, which has invaded many different ecosystems.
An evolutionary biologist at Humboldt University in Berlin, Gerhard Scholtz, has followed the spread of the marbled crayfish across the globe. The crayfish’s arrival in Madagascar threatens the success of several different species of crayfish that are native to the island. Because of how threatening the species is to native species, the EU has placed a total ban on the crayfish. It can’t be kept or distributed in any way.
The marbled crayfish is of interest to scientists for many different reasons. One of the primary reasons that scientists are researching the crayfish is that it may hold a key to treating cancer. Lyko says that the marbled crayfish is important to study because its asexual, self-replicating nature is a parallel for how cancer cells spread throughout the body. Lyko wanted to look at the genomes of the marbled crayfish to gain a greater understanding of the epigenetic mechanisms that allow it to clone itself. He hoped it would provide insight into how cancer spreads and tumors grow.
Sequencing The Genome
The sequencing of the Crayfish’s genome marks the first ever sequencing of a decapod genome. Decapods include crustaceans with 10-legs like crayfish, crabs, lobsters, and shrimp. Sequencing decapod’s genome took years, as the researchers had to stitch together fragments of DNA into an entire map of the genome. The sequencing of the crayfish’s genome means that comparative genomics and identification for decapods will soon be possible. The Crayfish’s genome may also be of benefit to conservationists, who can use the information unveiled to track how the invasive species spread.
The research revealed that although two of the Crayfish’s chromosomes sets are identical, the third chromosome set isn’t. Lyko’s research team believes that the third chromosome set likely came from the mating of two different slough crayfish, which gave rise to the marbled crayfish. One of the slough crayfish that mated with another slough crayfish likely had an abnormal egg or sperm cell that had two copies of its chromosomes instead of the usual one set.
Contrary to the usual situation where clones are at a disadvantage, due to having a lack of genetic diversity, the marbled crayfish is a surprisingly hardy species that is capable of thriving in a number of different freshwater habitats. The habitats have different salinity levels, acidity, and temperatures, yet despite these differences, the crayfish thrives in all of them. The crayfish’s three sets of chromosomes might play a role in its ability to adapt to different conditions. Some nematodes also reproduce asexually and have three sets of chromosomes. A greater level of adaptability means that species with three sets of chromosomes have greater success at invasions.
Sexual Vs. Asexual Reproduction
Studying the marbled crayfish could even help scientists determine why so many different animals have sex. There are clear benefits to asexual reproduction in the short term, but only around one in every 10,000 species consists of cloning females. In fact, over the long term asexually reproducing species tend to die out quicker than sexually reproducing species. Sexual reproduction may lead to the creation of species which are better at fighting off diseases, and more able to adapt to short-term changes in the environment.
Species that reproduce asexually tend to be more vulnerable to attacks from pathogens as well, mainly because if a pathogen can compromise the immune system of one clone, it can compromise every clone. Sexual reproduction increases how resilient a species is to pathogens.
The amazing thing about the marbled crayfish is that scientists have the chance to study a species with three sets of chromosomes and watch the evolution of an asexually reproducing species almost from the beginning of that species. The crayfish has managed to do extremely well over the past couple decades, but as the climate changes its fortunes could shift dramatically.
Lyko says that the fate of the marbled crayfish could really go either way, they could be wiped out due to their genetic similarity, or they could survive for 100,000 years. As Lyko notes, though 100,000 years seems like a long time to humans, it’s a brief moment on the timescale of life on our planet.