What makes ragweed so successful as an invasive species? • Earth.com

common ragweed (Ambrosia Artemisifoliaamazingly successful Invasive species. It is native to North America and was introduced to Europe in the late 19The tenth century. It has since been established in more than 30 European countries and is currently ranked the 12th “worst” in Europe, in terms of its environmental, social and economic impact. However, the reasons for the success of this resilient weed have not been investigated.

For as long as humans have traveled to different parts of the globe, they have carried with them seeds and spores of plants that did not belong – sometimes this was intentional, but often it happened unintentionally. In this way, humans have succeeded in changing the planet, as exotic species thrive in new territories and bring with them problems for native plants and animals, and for humans.

Exotic species that are currently becoming invasive pose one of the world’s major ecological problems as they overtake native species and take over their habitats. As a result, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) has identified invasive alien species as one of the biggest global threats to biodiversity.

Michael D. Martin, Professor of Evolutionary Genomics at Norwegian University of Science and TechnologyUniversity Museum (NTNU).

There are many examples of exotic plants and animals originating in new areas and causing havoc among native species. A good example of this is the rabbits that were introduced to Australia to make the place more like ‘home’. Within decades there were half a billion rabbits and their destruction of grazing and habitat was notorious. At the moment, on Marion Island in the sub-Antarctic, an expensive project is being carried out to eradicate inadvertently introduced mice that soon began work to eat the eggs of land-dwelling seabirds that breed there.

Despite many of these examples, not much research has been done on what makes some exotic species able to adapt to new environmental conditions and spread rapidly. So an international research group that includes some of the world’s leading genetic researchers has taken on the issue of common ragweed (Ambrosia Artemisifolia) in order to investigate potential source groups of ragweed introduced into Europe, to test whether there are fewer plant pathogens in Europe than in North America, and to identify possible genetic reasons for the success of ragweed groups in Europe.

To answer these questions, the researchers conducted an analysis of the genomes of ragweed plants, from North America and Europe. It also included specimens preserved in grasses, in order to gain a historical perspective on genetic changes in the populations of this plant and to understand how ragweed genomes have evolved since their introduction to Europe. They specifically searched for the genetic basis of the successful invasion of these plants. Their results have now been published in the journal science progress.

“We examined genetic material in 655 samples of common ragweed, of which 308 were from historical plant groups in the herb. “Some were as old as 190 years old, which is from the time the plant was first introduced to Europe,” says Vanessa C. Baker, an expert in evolutionary genetics at NTNU University Museum and lead author of the publication.

The results of the analysis showed significant changes in the genomes of ragweed plants in Europe over the past two hundred years, but not in those in North America. The researchers state that these changes likely reflect the introduction of ragweed from multiple diverse sources, as well as genetic drift during input bottlenecks. Furthermore, European ragweed samples showed evidence of genes from other delicious food The species they crossed with.

“We discovered that the plant crossed in Europe with closely related species that were introduced around the same time,” says co-author Michael Martin. This behavior meant that the common ragweed did not need the common ragweed plant nearby for breeding purposes as pollen from close relatives could be used to produce seeds. This is particularly useful in the early stages of introduction when population sizes were small.

In a more detailed analysis, the researchers found that genes associated with defense against pathogens, plant growth and flowering time were recently selected in European ragweed populations. “Invasive populations in Europe prefer to develop genes that contribute to their defense, such as genes against pathogens that cause disease,” Becker says.

When ragweed was introduced to Europe, it was less exposed to some of the more important pathogens than it is home in the United States. Some of the bacteria that commonly infect ragweed plants in North America were absent or rare in Europe, especially in France where the ragweed was first introduced. This type would have helped establish a stable group in France and helped spread it later.

Ragweed plant genomes from historical collections in France indicate that these early plants were derived from various sources. Eleven percent were genetically similar to plants from western North America, 15 percent bore the genetic signature to plants from eastern North America, and the majority (57 percent) were identified with plants from the Middle East. This indicates that ragweed was introduced several times to France alone, and may have been mixed with horse feed or seed bags.

Although Denmark is currently the northern limit of the common ragweed, it is now more established there. The plant is not a threat in Norway at the moment, possibly due to the country’s harsh climate. However, as global warming is altering global temperatures, the common ragweed is likely to be in its favour. It grows quickly, and it reproduces very successfully by using the wind to disperse its pollen. A single plant can produce about a billion grains of pollen per season, which causes a lot of discomfort to hay fever sufferers but means that sexual reproduction can be very effective in this species. Denmark’s common ragweed will likely not stop progressing, especially with the onset of the global warming effect.

The authors conclude that their study demonstrates the potential of global herbarium collections as a rich source of historical material for investigation of population genomics at continental, and even global, levels. These finely curated and often well-preserved plant specimens contain not only the genome of the host plant, but also a complex community of associated microbes that can reveal a rich history of coevolution during the Anthropocene.

by Alison BosmanAnd the Earth.com crew clerk

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