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Modified genes can distort the interactions of wild cotton with insects

Cotton plants native to the Yucatan Peninsula in Mexico may look the same: untidy, untamed shrubs with flowers that go from pale yellow to violet while pollinators visit them. But genes that have escaped genetically modified cotton crops have made some of these native plants fundamentally different, changing their biology and the way they interact with insects.

One type of escaped gene causes wild cotton to exude less nectar. Without any means to attract defensive ants to protect it from plant eaters, cotton will be devoured. Another escaped gene causes wild cotton to produce excess nectar, attracting many ants that can keep other insects at bay, including pollinators, researchers reported on Jan. 21 in Scientific Reports.

“They’re deeply interesting effects,” says Norman Ellstrand, an evolutionary biologist at the University of California, Riverside. “It’s the first case that really suggests that an entire ecosystem can be disrupted” after GMOs enter a wild population.

The results challenge a long-standing view that when genes from genetically modified crops escape nature, they only have a neutral effect on wild plants or pass on their benefits to weeds. for the knowledge and use of biodiversity in Mexico City. The findings confirm that the unexpected results of this gene transfer, some of which "were never imagined or at least not assumed to be possible," sometimes occur, she says.

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Scientists have already tried to explain what happens after the DNA of genetically modified crops ends up in their wild relatives (SN: 29/01/16). But most studies have been conducted under carefully controlled conditions and very few have tested the consequences, if any, of these gene transfers in natural ecosystems.

The few tests motivated Ana Wegier, a plant geneticist at the National Autonomous University of Mexico in Mexico City, and her students. The country was his natural laboratory. The cotton we know (Gossypium hirsutum) first appeared and diversified between 2 million and 1.5 million years ago in Mexico, and indigenous variants are still emerging throughout the land. In the last 25 years, vast fields of spongy, genetically engineered cotton have also sprung up in the northern part of the country.

During that time, Wegier explored Mexico in search of wild cotton, only to find it on the edge of cliffs, municipal landfills, or in the middle of a road. He wild cotton likes to grow in the most inhospitable places, where he does not have to compete with other species, she says. In 2018, Wegier and his group traveled to the Ría Lagartos Biosphere Reserve, an isolated coastal area on the Yucatan Peninsula. With the whitest beaches just a few feet away, the researchers spent long days observing and taking cotton samples under the scorching sun while swarms of mosquitoes bit non-stop.

ants on a white cotton flowerAnts patrol the flower of this cotton, preventing herbivores from devouring it.Valeria Vázquez Barrios

Back at the Wegier city lab, the team extracted DNA from the 61 plants it had collected and found that 24 of the plants had no GMOs. Twenty-one plants had a transgene that conferred resistance to the herbicide glyphosate; seven could now produce a lethal toxin that kills destructive insects; and the remaining nine had incorporated the two escaped genes into their genetic code.

With the nearest fields of genetically modified cotton nearly 2,000 miles away, “what surprised me most was how easy it was to find changes where we didn’t expect them,” says Wegier.

When combined in a stress-inducing chemical, glyphosate-resistant plants produced far less nectar than wild plants. Nectar is a sugary snack that wild cotton secretes whenever it is eaten in exchange for bodyguard services of especially aggressive ant species. These plants were also the ones that looked most irregular before taking the samples. With no tasty reward to offer and no ants to protect cotton from hungry herbivores, these plants suffered the most damage compared to native plants that did not have the GMO.

Treated with the same chemical, plants with the insecticide gene exuded nectar all the time, secreting more than wild plants with no escaped genes and becoming an irresistible beacon for protective ants. But in the researchers ’plant sample, there weren’t as many with the insecticide gene, suggesting that the ants or the transgene itself scared away other insects. This may have interfered with the pollination of the cotton flowers, preventing the plant from reproducing.

The findings are intriguing, says Hugo Perales, an agroecologist at the Southern Border College in Chiapas, Mexico, but urges caution. The uncontrollable real-world environment of Ría Lagartos has forced researchers to work with a very small number of plants, he said. "There's a suggestion that something is going on, but it needs to be verified."

For Wegier, the implications of the study are clear. As Mexico is the repository of the genetic diversity of cotton, he argues that it would be prudent to limit the introduction of more genetically modified variants. “We know that the presence of GMOs is irreversible and the (ecological) effects are irreversible,” he says.

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