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AUDIO 1 Dr. Marc Johnson describes how interactions between organisms and rapid evolution have
implications for agriculture:
25:09 - 29:55
“I love trying to understand how nature works – understanding the consequences of ecological and
evolutionary processes for the variation we see in nature and how that impacts human lives, whether it
be how we interact with nature on a day-to-day basis or how we try to manage nature when we grow
thousands or millions of acres of crops.
“For example, it’s becoming pretty clear that rapid evolution in some types of organisms can have a very
big impact in human lives, such as medicine and agriculture. I’ll give you a couple of examples:
“In the 1990s there was an increased use of a new crop variety of cotton that incorporated a gene called
Bt … Bacillus thuringiensis, this bacterium gene that has this toxin that’s extremely lethal to caterpillars
of moths and butterflies. Moths’ and butterflies’ herbivory causes huge losses in yield for cotton as a
result of their damage, so finding ways to mitigate that -- especially ways that are more environmentally
sound than spraying tons of pesticides on crops -- there’s a great need for that, and one method that
was developed was taking this gene from the bacterium and inserting it into the genome of cotton. It’s a
pretty routine procedure now -- inserting genes like this into different crop species.
“What Fred Gould here at NC State found was that very quickly a number of moth populations that are
big pests of cotton, particularly this one called Heliothis virenscens, evolved the ability to resist damage
or resist the toxicity of the Bt gene that had been inserted into cotton in just a handful of generations of
breeding. That’s pretty remarkable -- and a pretty major problem now that there are these moth
populations that can now feed on these cottons with the Bt resistance.
“So rapid evolution can have large ecological consequences that impact managed ecosystems like cotton
and agriculture, and we need to find ways to mitigate this.
“Some of the best ideas we have for mitigating this [are] trying to understand how nature works and
how natural plant populations are able to resist prolonged attacks by things like Heliothis for millions of
years. And one of the ways is sexual reproduction. …
“What it does from an evolutionary perspective is it shuffles the genes, just like shuffling cards in a deck
when you are dealing different hands. It changes the association among the genes within the genome,
and this leads to this moving target from an insect pest’s point of view -- so that unlike in a crop where
they can find the exact same genotype of that crop -- the crop with the exact same genes every single
year -- and adapt to that one genotype, within a natural plant population that’s sexually reproducing,
every single individual has slightly different genes. And every single generation the genetic composition
of that population is changing.
“And so it is much more difficult for an insect population to adapt to this changing environment (unlike
what we use in crops). … Maybe introducing the type of variation that we see in sexually reproducing
populations -- as opposed to these monocultures, that’s more akin to asexual reproduction -- might be a
way that we could develop to mitigate the evolution of counter-resistance to these pest populations.”