A Single Gene In One Species Can Cause Other Species To Go Extinct

An anonymous reader quotes a report from Scientific American: Some species play an outsize role in the environment they inhabit. Beavers build dams that create ponds where fish thrive. Otters in kelp forests eat enough sea urchins so that the kelp can grow without being gobbled up first. These so-called keystone species hold their ecosystem together. But what if ecosystems not only hinge on a single species but can be made or broken by a single gene? In a study published on Thursday in Science, researchers have demonstrated the existence of what they call a "keystone gene." The discovery may have implications for how scientists think about the ways ecosystems, and the species in them, persist over time. In the lab, the researchers built several miniature ecosystems that consisted of just four species each. At the bottom of the food chain was Arabidopsis thaliana, a small annual plant that is a favorite study organism among biologists (its genome was sequenced more than 20 years ago). In each ecosystem, the plant served as food for two species of aphids, which in turn fed a parasitoid wasp. Each bread-box-sized ecosystem contained multiple Arabidopsis plants. In some systems, the plants were genetically identical -- a monoculture. In others, genetic variations were introduced by turning on and off three genes -- MAM1, AOP2 and GSOH -- in various combinations.The researchers focused on these genes because they maintain the production of compounds called aliphatic glucosinolates, which protect the plant by deterring hungry aphids. Some of the experimental ecosystems had more variation in the number of genetic combinations than others; the researchers watched to see how well plants, aphids and wasps would coexist in each scenario. As the team expected, the ecosystems with more genetically diverse plants turned out to be more stable. For each plant with a different genetic makeup that the researchers added to the mix, the insects' extinction rate fell by nearly 20 percent, compared with monocultures. But what stunned the researchers was that this result seemed to hinge on a single gene. Regardless of diversity, if systems contained plants with a certain variant, or allele, of the AOP2 gene, the extinction rate of the insects decreased by 29 percent, compared with systems without it. Essentially, if you change that AOP2 allele, you lose the insects. Increasing genetic diversity helped the insects because it increased the likelihood of the aphids encountering plants with this one critical gene variant. [...] Also surprising was the mechanism by which the AOP2 allele impacted the aphids. Although the variant changed the way a plant produced its aphid-deterring compound, it also allowed the plant to grow faster. This in turn allowed the aphids, as well as the wasps that relied on them for food, to become larger faster.

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