14 DAY TRIAL // At a first glance, it may not look like a big deal, but some invasive plant species can change our life (the surroundings of our home) as we know it in unsuspected ways: humidity, fire regimes, and the soil composition, followed by flora and landscape changes.
The invasive plants often possess the advantage of escaping control, as in the new places they lack natural consumers and their populations soon bloom out of control.
In California, for example, they represent about 3 % of the total plant species, but they cover a much larger percentage of the state's surface.
A team at University of California, Riverside, found that manipulating the sexual requirements of some species could be a method to control their explosive spreading. The team employed as research species the wild radish (photo), planted in groups ranging in size from two to 20 plants.
The researchers checked if the Allee effect - a biological phenomenon claiming that the smaller and sparser a given population, the harder and slower it is for that population to resist in time - could be employed against new invasive plants.
Wild radish is a self-incompatible species (one individual cannot fertilize its own flowers), requiring another plant for reproduction, thus the team checked if its fertility is affected by population size and level of relatedness.
As in the case of humans, mates were more difficult to encounter in smaller populations and were most likely to be compatible if not related. "We call this the 'single's bar effect,'" said genetics Professor Norman Ellstrand. "Namely, that mating success increases both with the number of possible mates and their sexual receptivity."
The team experimented with populations of full sibling, half-sibling and unrelated plants.
Population size was the most important in determining the number of seeds per fruit (larger populations meant more seeds per fruit) while higher levels of relatedness induced less fruits per plant.
The Allee effect seems to be effective against invasive species if, for example, authorities who regulate the import of exotic plants permit the entrance of only one single genotype, decreasing this way the ability of seed propagation.
Wild radish entered California one century ago, brought by ships from Europe and currently inhabits all California, south from Baja California till north into Oregon. "Other invasive plants that need partners to reproduce and are found in California, include jointed goatgrass, Queen Anne's lace or wild carrot, marijuana and the wild sunflower," said Ellstrand.