A DNA study on the common Black Rat provides new insight into the ancient spread of rats, people, and diseases around the globe, say scientists.
An international team of researchers has studied the mitochondrial DNA of 165 Black Rat specimens from 32 countries around the world, and identified six distinct lineages in the Black Rat's family tree, each originating from a different part of Asia.
"Black Rats are carriers of many different human diseases, including plague, typhus and leptospirosis. It has been unclear why certain rodent-borne diseases are more common in some places than others, but our work raises the possibility that the different lineages of Black Rats each carry a different set of diseases, which is something medical science now needs to consider," says lead author of the study, Dr. Ken Aplin, who is a mammal expert at the Commonwealth Scientific and Industrial Research Organisation (CSIRO).
"We need to know more about what types of Black Rats are moving around the world and what disease risks each of them might pose. Our work raises the possibility that the different lineages of Black Rats each carry a different set of diseases," Dr. Aplin adds.
The researcher revealed that the six different lineages originated in India, East Asia, the Himalayas, Thailand, the Mekong Delta, and Indonesia.
The Indian lineage spread to the Middle-East around 20,000 years ago, and later to Europe. It reached Africa, the Americas and Australia during the Age of Exploration.
The East Asian lineage moved from Taiwan to Japan, the Philippines, and Indonesia, arriving in Micronesia only 3,500 years ago.
Although the other four lineages have not become so widespread, the researchers believe that they may be set to expand their ranges in the future.
"Our findings also show a good match between the historic spread of each lineage and ancient routes of human migration and trade, but there are a few surprises that raise new questions about human prehistory," Dr. Aplin says.
"The genetic evidence points strongly to there being more than one species of black rat, but more work is needed before we can say exactly how many species there are," adds the researcher.
Dr Aplin will present these findings at the Archaeological Science Conference in Canberra on Monday.