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Posted May 2009

Some of Australia’s weeds and pest animals could turn into climate change “super invaders” if we continue to import new strains of already established invasive species.

One big danger in bringing new forms of established invasive species into the country is the risk of arming weeds and pest animals with the genetic variability needed to quickly adapt to changing conditions under climate change.

The key to the problem is fixing our quarantine risk assessments, which are currently applied mostly to new species and not new genetic variants.

The risks were recently highlighted by Andrew Lowe, Chair in Plant Conservation Biology at the University of Adelaide, who said that in most cases super weeds become a problem after multiple introductions from different sources.

“By combining this genetic variation, new genetic mutations can arise that can give the alien species the potential to adapt and turn super-invasive,” Lowe said, referring to his own research and that of his colleagues’ comparing human-mediated introductions with natural colonisations (Wilson et al 2009).

The risks of multiple introductions under climate change were exemplified in a paper by Sebastien Lavergne and Jane Molofsky, from the University of Vermont, on one of the world’s worst invasive pasture grasses.

They found that multiple introductions of the invasive wetland grass canary reed grass (Phalaris arundinacea) from various parts of its native Europe into North America had given rise to novel genetic varieties through genetic reshuffling and recombination.

There was higher genetic diversity in its invasive range than in its native European range, and most of the invaders were recombinations of introduced European genotypes. The invaders had higher phenotypic plasticity, allowing them to compete for resources and space under a wide variety of environmental conditions. They were also larger and had other competitive advantages such as earlier emergence.

The researchers concluded that “multiply introduced invasive species are particularly predisposed to exhibit high rates of phenotypic evolution after their introduction, and may be very successful in adapting to predicted climate change in future decades.” They caution against repeated introductions of alien invasive species.

Many more studies in the past decade have documented examples of multiple introductions leading to invasiveness. Kiristina Schierenbeck, of the California State University, and Norman Ellstrand, of the University of California, listed 35 cases in which there is evidence that hybridisation preceded plant invasions.

Australia is in the process of developing new federal biosecurity laws in response to a 2008 federal government review. This creates an opportunity to address the risks of importing new strains of invasive plants and animals.

Federal environment minister Peter Garrett recently set a precedent for this by banning the import of savannah cat, on the basis that they would increase the threat of feral cats.

More information
Invasive Species Council’s backgrounder The invasion risks of introducing new genetic variants of exotic plants and animals (255KB pdf).

References
Lavergne S, Molofsky J. 2007. Increased genetic variation and evolutionary potential drive the success of an invasive grass. Proceedings of the National Academy of Sciences 104: 3883-3888.

Schierenbeck KA, Ellstrand NC. 2009. Hybridisation and the evolution of invasiveness in plants and other organisms. Biological Invasions 11: 1093-1105.

Wilson JRU, Dormontt EE, Prentis PJ, Lowe AJ, Richardson DJ. 2009. Something in the way you move: Dispersal pathways affect invasion success. Trends in Ecology and Evolution 24: 136-145.