Recent research from the University of Toronto Mississauga (UTM) on the impact of insects on plant populations have shown that evolution can occur faster than previously thought, even in a single generation. The study is published in the October 5 issue of Science.
"Scientists have long hypothesized that the interaction between plants and insects has brought so much diversity that we see among the plants, including agricultural crops, but until now we still have a limited direct experimental evidence," said Marc Johnson, Assistant Professor in the Department of Biology UTM. "This research fills a fundamental gap in our understanding of how natural selection by insects causing evolutionary changes in plants as they adapt, and shows how quickly such changes could occur in nature."
Johnson and his colleagues at Cornell University, the University of Montana and the University of Turku in Finland, evening primrose plant, a plant that is generally reproduce themselves and produce offspring genetically identical, to the two sets of plots. Each plot originally contained 60 plants of 18 different genotypes (plants that contain a set of different mutations).
Evening primrose moth caterpillar (Schinia florida)
eating regular evening primrose buds (Oenothera biennis).
Moths eating exclusively fruits and flowers of evening primrose and
in response to natural selection caused by these and other specialist moth,
populations of evening primrose flowers later develop and
produce high levels of toxic chemicals called ellagitannins in the fruit their fruits.
Evolution is effective in reducing damage to the reproductive organs of plants and
their offspring. (Credit: Marc Johnson)
To test whether the insects drive the evolution of plant defenses, one set of plots kept free of insects with insecticide applications regular biweekly during the study period. While the other received a plot set in the level of the natural insect.
Plots are allowed to grow without any other distractions for five years. Each year, Johnson and his colleagues calculate the number and types of plants that meet the plot.
They also analyzed the changes in genotype frequency evening primrose different and the properties associated with the genotype.
Johnson revealed that evolution, which is simply a change in genotype frequencies over time, was observed in all the plots after only one generation. Plant populations began to diverge significantly in response to insect attack in as little as three to four generations. For example, a plant that is free of insecticides has increased the frequency of genotypes associated with levels of toxic chemicals are higher in fruits, which makes them feel good to seed moth predators. Plants that bloom later, so avoid insect predators, with increasing frequency.
Johnson says the findings also suggest that evolution may be an important mechanism leading to changes in the ecosystem as a whole. "As the populations of these plants evolved, they change and influence the nature of their interactions with insects and other plant species, which in turn may develop adaptations to cope with these changes," said Johnson. "Abundance and competitiveness of the plant population is changing. Evolution can change the ecology and function of organisms and entire ecosystems. "
Additional ecological changes occurred in the plot when the insects are removed. Competing plants, such as dandelion, into two sets of plot, but is more abundant in plots without insects. This in turn reduces the amount of evening primrose plant.
Dandelion more use resource and also potentially prevent the light to reach the seeds of evening primrose, affecting seed germination. According to Johnson, ecological changes are the result of pressure from the moth caterpillars like to eat dandelions.
"What was demonstrated in this study is that changes in plant populations is not the result of genetic drift, but directly by natural selection by insects on plants," said Johnson. "It also shows how fast evolutionary change can occur - not over thousands of years, but over the years, and everything going on around us."
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