Plants can be infected by multiple viruses at once. However, the composition of the pathogen community varies, even if individuals belong to the same species and the same population. Ecologists have now shown that these differences are primarily due to genetic variation among the hosts. The loss of genetic diversity could thus render species more vulnerable to infections and extinction.

Viruses are ubiquitous across the plant and animal kingdoms — but most of them are still unknown to science. Researchers have only recently developed improved analysis techniques and statistical tools to tackle one of the key questions: Why are some individuals more susceptible to viruses, while others remain unharmed?

Combination of pathogens is important

It is already known that genetic differences can make animals or plants more resistant to a specific virus. However, it is becoming increasingly clear that most organisms do not only harbor one kind of pathogen but complex communities made up of different microbes. «Accounting for this diversity of infection is necessary to understand and predict disease dynamics and costs of infection for the host,» says Professor Anna-Liisa Laine from the Department of Evolutionary Biology and Environmental Studies at the University of Zurich. For example, the first arriving pathogen could confer resistance to a second pathogen. But so far, little is known about the factors that shape the composition of virus communities.

With her research team at the Universities of Zurich and Helsinki, Laine has now shown that genetic differences have a major impact on the diversity of the virus community each individual supports. «This suggests that depletion of genetic diversity within a species can have significant consequences for the risk of virus infection,» says Laine.

Identical plants in different environments

For their study, the team used the common weed Plantago lanceolata, also known as ribwort plantain. Individuals of this plant can be cloned by propagation of the roots — resulting in genetically identical offspring. With this method, the researchers generated 80 clones from each of four different genetic variants of ribwort plantain and placed them among populations of naturally occurring ribwort plantain at four locations in the Aland archipelago in the Baltic Sea. The cloned plants were thus exposed to virus attacks under natural conditions. «By placing identical plants in different environments and keeping everything else constant, we could rigorously test the role of genetics,» explains Laine.

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