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April 17, 2024

Environmental changes pressure viruses

By EVA PEKLE | February 14, 2013

We have all noticed that the temperature has been sporadically changing; one day it’s hot enough to put on our shorts, and the next, we would be freezing without our winter jackets. The random fluctuation in temperatures could turn out to have a larger impact than we thought. Recent studies showed that even viruses, which typically adapt more easily than mammals, failed to adapt when exposed to a random pattern of temperatures.

When one thinks of evolution, Darwin and the “survival of the fittest” may come to mind. In other words, a change in the environment forces populations to adapt. Species may undergo what is known as fitness trade-off, a phenomenon during which species evolve certain traits that are specifically advantageous in certain environments. For example, a moose can grow larger, which would effectively increase their strength to fight against others for territory, even though it can slow them down significantly.

If populations were subject to frequent environmental change, we can assume that these populations will continue to undergo rapid fitness tradeoff, increasing their likelihood to survive in specific conditions. However, when trade-off rates are high, a problem arises: the population-favored genotype may not be able to be fixed before a new turnover occurs again, leading to devastating situation for the species when the environment changes again. Thus, climate trends in the following years, along with random changes in temperatures and moisture, may cause certain organisms to eventually go extinct.

Barry Alto, assistant professor of arborvirology at University of Florida, along with colleagues at Yale University, published a study in Evolution, that suggests organisms that have a long life and low genetic variation, like cheetahs or polar bears, may fail to cope with unprecedented environmental conditions.

Alto and his team wanted to see how the temperature changes would affect organisms.

“Most organisms are poikilotherms and cannot self-regulate their temperature.  So, these organisms may be especially vulnerable to changes in environmental temperature,” Alto wrote in an email to The News-Letter.

They used the RNA vesicular stomatitis virus to carry their experiments.

“[It is] a model RNA virus used by many researchers to study evolutionary processes,” Alto explained. It also has other advantages such as having a simple genetic blueprint and, multiplying rapidly —in fact, a typical lab flask could culture millions or even billions of viruses. It can also be frozen indefinitely for archiving.

Alto described his experiment in the following way:

“We investigated the role of environmental temperature on the evolution of an RNA virus.  We evolved populations of vesicular stomatitis virus for approximately 100 generations in different temperature regimes: constant high, constant low, deterministically changing, randomly changing.”

One colony of virus was exposed to a constant temperature of 98.6 degrees Fahrenheit. The second one was kept at a constantly low temperature of 84.2 degrees Fahrenheit.  The third group was exposed to temperature that would be changing from high to low in a predictable pattern. Finally, the last batch of virus was exposed to temperatures varying from high to low in a random pattern.

“To carefully control the population sizes, it required transferring a sub-sample to a new host environment every 24 hours.  Because the process of doing the transfer took several hours, it was necessary for me to come into the laboratory at all hours day and night in order to perform the passage of viruses to the new host environment.  Doing this for approximately one month gets old really fast,” Alto confessed.

The scientists then compared the fitness of those new generations of virus to the fitness of the original ancestral form. They found that the viruses that were exposed to the variable but predictable temperature pattern were the most fit; the viruses exposed to constant high and constant low temperatures weren’t as robust, but survived adversities to a greater extent than the viruses that were exposed to random temperatures.

The latter was not able to adapt to the unpredictably changing environment. This finding was a surprise to the researchers.

“To our surprise, we did not observed strong effects of fitness trade-offs,” Alto said.

The fact that even viruses, which are some of the most adaptable organisms, had a hard time adapting to the changing environment should alarm us to some extent; there is very little hope for animals that are long-lived and that have few mutations to be able to cope with the future environmental conditions that may arise randomly.

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