The green crab (Carcinus maenas) is considered to be one of the worst invasive species in the world, which is native to Atlantic Europe and has been introduced to various places across the globe, according to Invasive Species Compendium. It is an omnivore that devours different species that range from plants to animals. reported that green crab had shown an extensive global invasive range. At first, scientists assumed that their successful populations had high genetic diversity or specific characteristics that helped them adapt to different environments. However, they found that the green crab is like any other invasive species with low genetic diversity.

 European Green Crab Showed Extensive Dispersal Despite High Gene Flow, Low Genetic Diversity
(Photo: Wikimedia Commons)
European green crab (Carcinus maenas)

Adaptive Mechanisms of the Green Crab Despite Having Low Genetic Diversity

Researchers from the Woods Hole Oceanographic Institution led by Carolyn Tepolt, an associate scientist of biology, are investigating the green crab's adaptive mechanisms that have shown extensive dispersal across the west coast of North America despite having low genetic diversity.

In the study, titled "Balanced Polymorphism Fuels Rapid Selection in an Invasive Crab Despite High Gene Flow and Low Genetic Diversity," published in Molecular Ecology, researchers focused on the European green crab that has spread throughout the northwestern Pacific since it was introduced 35 years ago.

Tepolt and her team examined the genetic structure of green crabs across six locations that are 900 miles from central California to British Columbia. They found a piece of DNA responsible for cold tolerance that appears to be under strong selection from north to south based on their previous study.

Researches noted that although this may look like a balanced polymorphism that evolved to help the species adapt to its environment despite high gene flow, these populations have gone through extreme bottlenecks that dramatically decreased their genetic diversity.

According to, this study highlights the need to consider that diversity in some parts of the genome may impact how they adapt to a new or changing environment.

Tepolt explained that the findings indicate a partial resolution of the "genetic paradox of invasions" as it demonstrates variations in crucial parts of the genome that allow them to thrive in a population with low genetic diversity. Moreover, it also suggests high gene flow in populations of species far from their native range, which provides species the characteristics for rapid adaptive change.

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Identifying Invasive Species

 As humans get better at moving stuff around the world, there is a high possibility that species come along for the ride and expand to new environments but end up being invasive species. Tepolt said that non-scientists who spot invasive species should immediately report it to officials and researchers, such as when they spot green crabs in an area for the first time.

The National Wildlife Federation defines invasive species as an organism that is not native to an ecosystem and causes harm to the environment, economy, or human health. These species rapidly grow and aggressively spread with the potential of causing harm, hence the term "invasive."

The federation noted that an animal does not necessarily need to come from another country. A species that is native to a local area but is seen in another local area causing harm, such as competing for resources, could be considered an invasive species.

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