ODU study's findings could affect oyster debate for Bay

NORFOLK

In 1899, an English ship stopped at Christmas Island, near Australia. Within nine years, the island's entire native rat population had gone extinct, and scientists have wondered ever since what exactly happened.

Now, researchers led by an Old Dominion University scientist think they have unraveled the mystery - and, they say, the lessons of Christmas Island apply today to issues such as disease, invasive species and the law of unintended consequences.

Turns out, says ODU biology professor Alex Greenwood, that a British black rat had stowed away on the ship in a bale of hay. Upon reaching the island, the rat - or several rats - escaped on land and spread a "hyperdisease" among the native population.

"Anyone who has ever tried to kill a rat - let alone a whole population - knows how hard that can be," Greenwood said in an interview Monday. "That's what made Christmas Island so fascinating for so long. Imagine, a whole species - especially one as tough as a rat - gone within 10 years of exposure!"

The study by Greenwood and eight colleagues, including ODU graduate student Kelly Wyatt, is published in this month's PLoS One, a scientific journal.

It is being celebrated as the first evidence for extinction of a mammal entirely because of disease.

The results come as Virginia and Maryland are pondering a possible introduction of a foreign oyster species into the Chesapeake Bay to help restore stocks. Concerns about the Asian oyster carrying a new pathogen to the Bay or sparking an unforeseen disease "is definitely an issue" and "should be considered very, very carefully," Greenwood said.

"The chances for a new pathogen are very high, and should be seen as a high risk," he said.

Greenwood, who came to ODU two years ago from Germany, said disease often is overlooked as a root cause for an animal or plant species struggling to survive in the wild. But, he said, disease is probably playing a larger-than-expected role in the decline of Tasmanian devils, African wild dogs and North American amphibians, including the common frog.

Conventional wisdom for years has stated that the frog is likely suffering the side effects of global warming. But recent research indicates this explanation is too simplistic, if not entirely wrong, Greenwood said.

"It seems to indicate a pathogen is more to blame," he said. "Now, climate change might have exaggerated the impact of the pathogen, but it's a pathogen that appears to be the underlying issue."

Humans probably cannot be wiped out by a hyperdisease, Greenwood said, "because there's just too many of us at this point." Still, he noted how the plague, Ebola and influenza have killed scores of sickened people throughout history, which makes "localized extinction probably a possibility, though a very remote one."

The Christmas Island study started nearly five years ago, when Greenwood and colleagues from New York and Copenhagen were allowed to take DNA from dead, native rats in a museum collection.

The data indicated the presence of a protozoan known as Trypanosoma lewisi. A related organism can cause sleeping sickness in humans.

The finding seemed to make sense of field observations from 1905 that some native rats on Christmas Island could be seen stumbling down footpaths, as if delirious or extremely tired.

Greenwood described the study "as certainly one of the biggest" papers he has ever had published in his career.

He next hopes to complete research on the reasons why the woolly mammoth went extinct. Greenwood suspects disease played a key role in the great beast's disappearance from Earth.

Scott Harper, (757) 446-2340, scott.harper@pilotonline.com