Based on the article written by Craig Packer,
Associate professor of biology at the University of Minnesota

In January 1979 Craig Packer with colleague and wife Anne Pusey, began their study of lions in Nogorongoro Crater, a 2,000-foot-deep caldera with a hundred square mile floor located at the eastern edge of Tanzania's Serengeti Plain. The craters's cliff walls serve to isolate about 100 lions from their nearby Serengeti counterparts.

Suspecting the lions were subjected to repeated inbreeding and that they may conceal genetic vulnerabilities, the Packers set about reconstructing the family tree of at least five generations of every lion that lived in the crater. The scientific mystery would take ten years to solve.

Each lion on the crater floor between 1975-1978 had been carefully catalogued on an ID card by the previous wife and husband research team of Jeannette Hanby and David Bygott, with one side of the ID card containing a series of closeup photographs, and a stylized drawing of the lion's face one the other. The drawings emphasized markings on an individual's face including scars, ear notches, and the whisker spots on either side of its muzzle. Whisker spots are the Morse code of lion identification -- a permanent signature of each individual which is present at birth and never changes -- and as unique as a human fingerprint.

There were two reasons to suspect the crater lions were inbred:

• No new lions had entered the crater during the previous four years
• A report suggesting the population of crater lions had been devastated by a plague of biting flies in 1962

A Recent History
According to Henry Fosbrooke, conservator of the Ngorongoro Conservation Area during 1961 and 1962, exceptionally heavy rains permitted the biting fly Stomoxys calcitrans to breed constantly for more than six months. By May 1962 the crater had switched from heaven to hell for the lions. Most lions became emaciated and covered with festering sores, and while many sought shelter by climbing trees or hiding in hyena burrows, they eventually became so ill they were no longer able to hunt. By the time the rains finally abated, Fosbrooke estimated the population of at least 70 lions had been reduced to about ten.

By 1972 the population was reported to have recovered to its former levels and was distributed among three prides and by 1975, the Bygotts reported lions on the crater floor dispersed among five prides.

The Packers invited Steve O'Brien at the National Cancer Institute and his colleagues from Washington's National Zoo to conduct genetic studies of the crater lions in 1984. O'Brien had surveyed the genetics of several different cat species through his research on feline leukemia. Genetics and reproductive physiology of the crater lions were assessed by comparing them with the nearby Serengeti lions, since long-term studies of the Serengeti population had shown that close inbreeding is almost nonexistant in that area.

"With complete reproductive records of the population since 1963, we could test whether inbreeding has lowered the productivity of the population. We now estimate that the crater lions have lost about 10 percent of their genetic diversity over the past 20 years. Our estimates of this decline are closely correlated with a reduction in reproductive rates in the crater lions, although it is too soon to be certain of a direct link. If inbreeding has indeed caused this reduction, then reproductive rates in the crater population will continue to decline in the future unless new males are once again able to enter the crater.

"The crater lions also show somewhat lower genetic diversity than can be attributed solely to the effects of the Stomoxys plague. The crater has been naturally isolated for millennia, and its lions may have undergone several cycles of isolation, decline, and repopulation. It is possible that the previous population was highly susceptible to the depredations of the biting flies precisely because they were already quite inbred..

"I visited Henry Fosbrooke again in October 1990. When I told him that I suspected the crater lions had been through previous periods of genetic decline, he led me into his large library and said, 'You should read these.' They were accounts of big-game expeditions that went into the crater in the early twenties. During two weeks in 1922 one hunting party bagged seven adult lions and badly wounded another three. The last expedition was in 1924, when five more lions were killed. Considering that there are never more than about 30 adult lions in the crater and that most of the wounded animals probably died as well, the breeding population must have been severely reduced. Our genetic assays more than 60 years later may well have revealed the results of this onslaught.

"The Serengeti and Ngorongoro were declared wildlife sanctuaries in the late twenties to protect the lions from further hunting. Ngorongoro Crater became a world heritage in 1979 in recognition of its special significance as a microcosm of African savanna. The popular appeal of charismatic carnivores such as lions has often led to the conservation of habitat that sustains a host of other species. But living at the top of the food chain inevitably means that predators often end up in small, threatened populations.

Craig Packer, an associate professor of biology
at the University of Minnesota,
has studied East Africa's lions since 1978.