Crayfish That Could Take Over the World

Decapods are amongst some of the most notorious invasive species across the globe. Generally, some of their reproductive attributes make them such superior invasive species. They grow fast also and reach sexual maturity relatively quickly, especially in warmer tropical habitats. They are highly fecund, with some producing hundreds of thousands of eggs in a single brood. Some can produce multiple broods per year and can even store sperm from multiple males.

Crayfish are decapods and can be important keystone species in their freshwater ecosystems. A number of crayfish species are considered invasive species around the world. One species, the marble crayfish, Procambarus virginalis, is on the invasive hitlist and the European Union and two US states have already banned the marbled crayfish from being owned or traded.

The major issue of concern with P. virginalis is a mutation which permitted parthenogenesis. Parthenogenesis is a form of asexual reproduction where growth and development of embryos occur without fertilization. In other words, female crayfish can reproduce without males. A new study in Nature Ecology and Evolution has finally published the entire genome of this important species. Dr. Wolfgang Stein describes, "If you have one animal, essentially, three months later, you will have 200 or 300". Stein and his team at the German Cancer Research Centre are hoping to better understand how cancer tumours adapt and develop resistance to drug treatments, by studying the crayfish's adaptability and ability to multiply. The marbled crayfish’s three sets of chromosomes may be essential, providing the necessary genetic variety for adapting to different conditions.

P. virginalis raised alone in captivity tended to be more blue than those socialised with other species. Animals sequenced in the US were more blue than those from Europe and Madagascar.

But how did this all happen? In a German pet shop in the 1990’s descendants of the slough crayfish, Procambarus fallax, produced a female with an additional set of chromosomes. This mutation allowed for apomictic parthenogenesis, permitting her and her clone offspring to spawn hundreds of eggs at a time without mates. Over time, popularity among aquarium hobbyist, resulted in its anthropogenic spread, releasing into ponds and lakes across Europe. The marbled crayfish has now been found as wild populations in the US, Japan, Madagascar and multiple European countries. First introduced into Madagascar as a cheap source of protein, the species is now threatening endemics, creating an ecological nightmare for authorities.

Now that Stein and his research group have sequenced the crayfish’ genome many more questions can begin to be asked. It will help provide a better understanding of its distribution, its origins/movement/spread across the globe, its diversification and its ability/plasticity to adapt to new environments. Identifying relevant genetic variation in the marbled crayfish could identify other genes of significance to help in the study of other invasive decapods.

For the full text please see https://www.nature.com/articles/s41559-018-0467-9

Gutenkunst J, Andriantsoa R, Falckenhayn C, Hanna K, Stein W, Rasamy J, Lyko F (2018) Clonal genome evolution and rapid invasive spread of the marbled crayfish. Nature Ecology and Evolution. doi:10.1038/s41559-018-0467-9