Analysis of the genome of an invasive crustacean Eurytemora affinis showed that for successful colonization of fresh waters has produced their lives in an unstable environment, estuaries and brackish waters. Balancing selection acting here on the populations of crustaceans, maintained a high level of genetic diversity, which was useful in the capture of a new environment. As noted by the authors of the research article for the journal Nature Ecology and Evolution, the same mechanism may contribute to the success of other species-invaders.
The spread of invasive species is considered one of the major environmental issues of our time. Unfortunately, opportunities are limited because of lack of knowledge. For example, scientists are still unclear why some species have had to learn fast in a new place and captured a huge territory, while others fail and fade.
According to one hypothesis, the success of invasive species is determined by the conditions in his homeland. Best invaders become organisms adapted to life in disturbed or volatile environments, which due to balancing selection favor the maintenance of high genetic diversity. When a species is in an unusual situation, a large number of genetic variants allows him to quickly adapt to it.
This idea seems plausible at least for some species and situations, but still nobody tried to confirm it empirically. To do this it was decided David stern (David Stern Ben) and Carol Lee (Carol Eunmi Lee) from the University of Wisconsin in Madison. They drew attention to the copepods belonging to the species complex Eurytemora affinis. Initially, these invertebrates inhabited the brackish waters and estuaries, however, due to water transport over the last 70 years has widely spread in fresh waters.
In the native habitat of E. affinis is faced with unstable conditions, including fluctuations in salinity and drought periods suffered in the form of eggs. This makes it an ideal object for testing the hypothesis about the influence of balancing selection on the success of invasive species.
The researchers collected one hundred samples of shrimps from various North American populations, both natural and inhabit the newly captured area. Each of them had full genome sequencing, and identified loci undergoing balancing and driving selection.
It turned out that the descendants of natural populations of E. affinis from the Atlantic ocean and the Gulf of Mexico at least three times independently from each other, passed to life in fresh water. However, in each case, the selection was influenced by similar sets of genes, associated with freshwater lifestyle. First of all, talking about the genes that produce proteins for transport of ions.
As predicted by the authors, the majority of genetic variants that influence the driving selection after infection, and maintained in natural populations due to balancing selection. Rather, they appeared to maintain, since E. affinis was regularly confronted with drastic changes in salinity in their native habitat.
According to the authors, the results of the analysis provided the first evidence that balancing selection in unstable environments may give species a genetic basis for rapid acquisition of new habitats. In the future the researchers hope to provide more rigorous evidence of the reality of this mechanism. In addition, they plan to conduct a similar analysis for other invasive species occurring in unstable habitats, e.g. river bivalves Zebra mussel (Dreissena polymorpha),
Invasive species are very diverse, but they all share the ability to thrive away from home. To learn more about these living organisms and the attempts of humanity to deal with them you can from our test, “Immigrants or invaders?”.