YSM Issue 86.3

BY MAHBUBA TUSTY
VIROLOGY
Can Viruses Adapt to Erratic Temperatures?
Yale researchers led by Professor Paul Turner of the Ecology and
Evolutionary Biology Department have shown that viruses have
significant difficulty adapting to rapidly changing temperatures.
Although viruses are known for their adaptability under different
environmental conditions, Turner found that they suffer when
temperatures change too unexpectedly. His findings are especially
relevant in the face of the rapid temperature changes predicted by
various climate models. If viruses like the ones which cause the
common cold fail to adapt to temperature changes despite their
simple structure, what does this research imply for other, more
complex animals such as polar bears or even humans?
For this particular project and many others, Turner used the
vesicular stomatitis virus, a popular subject for studies in viral evolution.
It contains only five genes that evolve very quickly, making
the virus ideal for laboratory use. Within a day, Turner produced
four generations of the virus. and eventually created 100 generations
in total for the study.
Turner and his team then divided these viruses into four groups
and assessed their ability to adapt to different set temperatures.
The first group was tested at 37 degrees Celsius, approximately the
temperature of the human body and a standard temperature for
research. Next, the researchers tested another group of viruses at
29 degrees Celsius, the “low temperature” for the experiment. The
third group of viruses was exposed to both the low and high temperatures
on alternating days. Finally, the fourth group in the study
was subjected to erratic temperature changes, where temperatures
ranged anywhere from 29–37 degrees Celsius on any given day. The
goal of the experiment was to assess the phenotypic and molecular
changes of the viruses under the different temperature conditions.
If the viruses underwent significant mutations at their respective
temperatures and produced significant phenotypic change, they
increased their fitness. If they failed to do so, their adaptability and
therefore their fitness
left them susceptible to
destruction.
The results showed
that viruses had the highest
fitness gains in the
alternating, yet predictable
temperature pattern
(group three). Viruses
in the two treatment
groups (groups one and
two) which employed
constant temperatures
IMAGE COURTESY OF UNIVERSITY OF
WISCONSIN-MADISON
Glycoproteins on the surface of the
virus enable invasion into host cells
and may be the most affected by
temperature changes.
had the next highest fitness
gains. The viruses
in the final group, which
encountered the random
temperature changes,
had the lowest fitness
gains. This means that
IMAGE COURTESY OF THE CENTERS FOR DISEASE CONTROL AND PREVENTION
Arthropod-borne viruses, such as the vesicular stomatitis
viruses shown in thie electron micrograph, are used by the
Turner Lab as experimental models.
the viruses exposed to erratic temperatures were the least successful
in adapting and improving their likelihood of survival.
The viral gene that produces glycoprotein, which is responsible
for virus entry into the host cells where it reproduces, seems to
be the gene most affected by the temperature changes. Across all
the temperatures tested, the majority of genome substitutions
occurred there. This suggests that glycoprotein plays a key role
in supporting the viruses’ vitality as temperatures change, though
what that role could be is not yet fully understood. As a result, the
functional role of the glycoprotein in temperature adaptation is
the next area of interest to Turner’s group.
These results would seem to beg the question: Are the kinds of
rapid changes in temperature Turner used in his study prevalent
in the real world? “If you don’t like the weather in New England,
wait a night,” Turner answered. “In many parts of the United
States and around the world, the weather already changes by eight
degrees from day to day.” He added, “if we shift our frame of
reference to the world, the change might not be as astounding just
yet.” However, climate models currently in use or in development
show that these kinds of temperature jumps are certainly plausible.
If viruses, the most adaptable life form known, are unable to
adapt to such changes in temperature, how can other species expect
to do so? If efficient reproductive machines such as viruses cannot
adapt to fluctuations in an eight degree window of temperature
change, then what can the koalas or polar bears of the world do
in the face of climate change? Finally, what does climate change
coupled with Turner’s findings imply about the survival capability
of the human species? Of course, much research is needed to
address these questions, and it is for this reason that Turner urges
the government to allocate more money for basic research at Yale
and throughout the nation. “I worry about the future of scientific
research,” he concluded. “I worry about the world my children will
live in without the discoveries made possible by basic research.”
www.yalescientific.org April 2013 | Yale Scientific Magazine 11