Insects a prime driver in plant evolution and diversity, study finds

Oct 04, 2012
A caterpillar of the evening primrose moth (Schinia florida) devouring a flower bud of common evening primrose (Oenothera biennis). These moths exclusively feed on the flowers and fruits of evening primrose and in response to natural selection imposed by this and other specialist moths, evening primrose populations evolve to flower later and to produce high levels of toxic chemicals called ellagitannins in their fruits. This evolution effectively reduces damage of the plant’s reproductive organs and progeny. Credit: Marc Johnson

Take a good look around on your next nature hike. Not only are you experiencing the wonders of the outdoors – you're probably also witnessing evolution in action.

New research from the University of Toronto Mississauga (UTM) on the effect of insects on plant populations has shown that evolution can happen more quickly than was previously assumed, even over a single generation. The study is to be published in the Oct. 5 issue of Science.

"Scientists have long hypothesized that the interaction between and insects has led to much of the diversity we see among plants, including crops, but until now we had limited direct ," says Marc Johnson, Assistant Professor in the UTM Department of Biology. "This research fills a fundamental gap in our understanding of how natural selection by insects causes in plants as they adapt, and demonstrates how rapidly these changes can happen in nature."

Johnson and his collaborators from Cornell University, University of Montana and University of Turku in Finland, planted evening primrose, a typically self-fertilizing plant with genetically identical offspring, in two sets of plots. Each plot initially contained 60 plants of 18 different genotypes (plants that contain different sets of mutations).

The larvae of the seed feeding moth Mompha brevivitella devouring the seeds of common evening primrose (Oenothera biennis). The larvae of this moth exclusively feed on the fruits of evening primrose and in response to natural selection imposed by this and other moth species, evening primrose populations evolve to flower later and to produce high levels of toxic chemicals called ellagitannins in their fruits. This evolution effectively reduces damage to the plant’s seeds. Credit: Marc Johnson

To test whether insects drive the evolution of , one set of plots was kept free of insects with a regular biweekly application of insecticide over the entire study period. The other set of plots received natural levels of insects.

The plots were left to grow without other interference for five years. Each year, Johnson and his collaborators counted the number and types of plants colonizing the plots. They also analyzed the changing frequencies of the different evening primrose genotypes and the traits associated with these genotypes.

Johnson says that evolution, which is simply a change in genotype frequency over time, was observed in all plots after only a single generation. Plant populations began to diverge significantly in response to insect attack in as few as three to four generations. For instance, plants that were not treated with had increases in the frequencies of genotypes associated with higher levels of toxic chemicals in the fruits, which made them unpalatable to seed predator moths. Plants that flowered later, and thus avoided insect predators, also increased in frequency.

Johnson says the findings also show that evolution might be an important mechanism that causes changes in whole ecosystems. "As these plant populations evolve, their traits change and influence their interactions with insects and other plant species, which in turn may evolve adaptations to cope with those changes," says Johnson. "The abundance and competitiveness of the plant populations is changing. Evolution can change the ecology and the function of organisms and entire ecosystems."


Video: Anurag Agawal provides hard evidence of evolution. Credit: National Science Foundation

Additional ecological changes occurred in the plots when insects were removed. Competitor plants, such as dandelion, colonized both sets of plots but were more abundant in plots without insects. This in turn reduced the number of evening primrose plants. The dandelion used more resources and also potentially prevented light from reaching the evening primrose seeds, impacting seed germination. According to Johnson, these ecological changes were the result of the suppression of a moth caterpillar that preferred to feed on dandelion.

"What this research shows is that changes in these were not the result of genetic drift, but directly due to by on plants," says Johnson. "It also demonstrates how rapidly evolutionary change can occur – not over millennia, but over years, and all around us."

Explore further: Natural born killers: Chimpanzee violence is an evolutionary strategy

More information: Insect Herbivores Drive Real-Time Ecological and Evolutionary Change in Plant Populations," by A.A. Agrawal et al., Science, 2012.

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User comments : 4

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kevinrtrs
1 / 5 (9) Oct 04, 2012
Sure, so evolution is super quick then:
Johnson says that evolution, which is simply a change in genotype frequency over time, was observed in all plots after only a single generation


The question one has to ask is whether this kind of "evolution" is responsible for all the different life-forms we encounter today? Did these all arise from just a single organism, in fact a single "first ancestor"?
Did the frequency of genotypes change so dramatically over supposed billions of years? Does a change in genotype frequency actually lead to new functionalities and shapes and forms that are radically different from the original organism's constitution?
Does it lead to the solution of irreducibly complex physiological engineering problems in one single step without any intermediate steps?

I beg to differ from the accepted dogma.
aroc91
5 / 5 (5) Oct 04, 2012
Do your job, moderators. Kevin should have been banned for religious trolling years ago. The fact that he remains here is irrefutable evidence to your ineptitude.
dxer
1 / 5 (5) Oct 05, 2012
Johnson has observed a change in the genotype frequency. He has not observed the emergence of new genotypes or traits. Still he is able conclude that "Evolution can change the ecology and the function of organisms and entire ecosystems."
Johnson is also able to extrapolate.

depth
3 / 5 (2) Oct 05, 2012
Johnson has observed a change in the genotype frequency. He has not observed the emergence of new genotypes or traits. Still he is able conclude that "Evolution can change the ecology and the function of organisms and entire ecosystems."
Johnson is also able to extrapolate.
This is a joke isn't it . you are here troll aren't you .