Genes reveal migration secrets of the Black Rat

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The Black Rat, Rattus rattus.

The black rat (Rattus rattus) is the most important mammalian pest on Earth. They cause huge damage to crops and food in storage and spread bacterial and viral diseases including the plague, leptospirosis, rat-bite fever and salmonellosis.

So where did black rats come from and how did they manage to reach most corners of the globe with such devastating success?

Professor Steve Donnellan and his team at the South Australian Museum’s Evolutionary Biology Unit (EBU) are finding answers by tracing the genetic history of Rattus rattus. Preliminary results from the research suggest that the rats we see today originated from two different regions — India and Indo-China. Genetic analysis has shown there are actually quite a few discrete populations of black rats around the world. The team is now trying to determine if these different types of black rats are discrete species.

The results of genetic studies have opened up the possibility of tracking rat migrations. As there are subtly different populations of black rats, each group can be tracked individually and their movements around the world over time mapped with greater sensitivity.

Early results are very exciting for Steve and his research group. It appears that the capacity of black rats to move around the world was closely linked with the development of agriculture. When stored grains began to be transported from continent to continent, different populations of rats followed.

The studies, conducted primarily by University of Adelaide students Andrew Wiewel (PhD) and Hugh McColl (Honours), involved analysing DNA from frozen and preserved black rat tissue samples collected from southern and south-east Asia. Tissues were also collected from locations where the black rats are regarded as introduced, including Australia, New Zealand, North and South America, Europe, the Middle East and Africa.

In the next phase of this project, the team will try to isolate ancient DNA from rat remains. Highly possible given the frequency at which black rat bones occur in archaeological digs.

This research was funded with a Discovery Grant from the Australian Research Council.