Inbreeding Of Species CanLead To Extinction, Scientists Say

Inbreeding Of Species CanLead To Extinction, Scientists Say

WASHINGTON (November 26, 1998 8:57 p.m. EST http://www.nandotimes.com) - Scientists examining endangered prairie chickens said on Thursday they had confirmed that inbreeding can propel a species down the road to extinction.

Pinpointing the causes of extinction has long been a controversial issue among scientists. Some have argued inbreeding is the critical factor leading to a species' demise, while others maintain environmental conditions such as habitat loss are the more important players in extinction.

But a team of researchers at the Illinois Natural History Survey and the University of Illinois have shown the answer is probably a combination of both factors.

"I think this is going to put a nail in the coffin of separating the parts of genetic and nongenetic factors when talking about extinction," said L. Scott Mills, a wildlife ecologist at the University of Montana who commented on the study in the journal Science.

"What they have done is swing the pendulum back toward the middle," he said in a telephone interview, adding the study is one of the first to fully document examples of the complex interactions between the factors that push a population toward extinction.

Over 35 years the researchers tracked the reproductive success, genetic makeup and total number of Illinois prairie chickens, which numbered 2,000 in 1962 but had fallen to fewer than 50 by 1994.

As the prairie chicken population decreased, genetic variation diminished, Mills said. A lack of genetically different mates led to subtle changes in birth and survival rates and made it less likely an egg would hatch, which helped speed the birds' demise, he explained.

But the study also pointed out inbreeding alone does not lead to extinction. Habitat loss and other environmental factors play an important role in diminishing a population to a level where inbreeding can quicken extinction, said Ronald Westemeier, a wildlife ecologist, who led the study.

"We believe the near-complete loss of suitable grasslands and satellite populations in the region drove the greater prairie chicken toward this scenario," the authors wrote in Science.

There is also evidence that once a population size tumbles far enough it can reach a point of no return where nothing can counter the effects of inbreeding, Westemeier said.

The Illinois prairie chicken population only rebounded when the researchers diversified the gene pool by importing birds from neighboring states. This showed the importance of maintaining sufficient genetic resources for a species survival, Westemeier pointed out.

"All we are saying is you reach a critical level in gene pool levels that will affect reproduction rates and no amount of habitat restoration can help anymore," Westemeier said.

By Michael Kahn, Reuters News Service