I Smell An Invasive Rat

Genetic tests pin down origins of island-hopping rodents

After managers try to eliminate an invasive species from an ecosystem, the pests can sometimes turn up again. But are the animals survivors of the eradication or new invaders from a different region?

The answer is important for pest managers because it determines whether the original eradication attempt worked, researchers say in Biological Invasions. If the animals are survivors, the strategy may need to be changed – a potentially costly process. On the other hand, a reinvasion might mean that security needs to be strengthened.

The team studied one scenario at Pearl Island, New Zealand, an area that was invaded by three rat species. After managers attempted to stamp out the pests in 2005, 13 rats were found in 2006, and one species spread across the island by 2007. To find out where the rodents had come from, the researchers analyzed the DNA of rats from Pearl Island, both before and after eradication, as well as from neighboring Stewart Island.

The newly discovered rats bore the genetic traits of the Stewart Island population, the team concluded. So while the eradication succeeded, rats appear to be swimming to Pearl Island faster than expected. The researchers say that similar tests could be used to evaluate other eradication campaigns, as long as managers collect samples of the species before removal. – Roberta Kwok

Source: Russell, J., Miller, S., Harper, G., MacInnes, H., Wylie, M., & Fewster, R. (2009). Survivors or reinvaders? Using genetic assignment to identify invasive pests following eradication Biological Invasions DOI: 10.1007/s10530-009-9586-1
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