A Surprising Discovery About Cheetah Biology

In the late 1970's, the National Zoo in Washington, D.C., asked David E. Wildt, then a biomedical researcher working with domestic cats, for help with the cheetah. Wildt collected sperm samples from captive cheetahs belonging to several American zoos. By looking at the samples under a microscope, he found to his surprise that about 70 percent of the sperm were abnormal. The abnormal sperm appeared damaged, with strangely bent or coiled tails or other deformities that would prevent them from penetrating and fertilizing a female's egg.

At first, Wildt thought the abnormalities in the cheetahs' sperm must be a result of the stressful conditions under which most zoo cheetahs were kept. Then, in 1981, Wildt went to South Africa to perform similar studies on male cheetahs at the DeWildt Cheetah Breeding and Research Center, near Pretoria. The South African cats, most of them bred in captivity but including some caught in the wild, showed the same level of sperm abnormalities as cheetahs in U.S. zoos.

To help determine why the cheetah had such high rates of abnormal sperm, Wildt sent blood samples from each male cat to Stephen J. O'Brien, a researcher at the U.S. National Cancer Institute in Bethesda, Md. O'Brien wondered whether the cheetah's reproductive problems were due to a genetic problem, possibly a lack of genetic variation among individual cats. Genes are components of living cells that contain the blueprint for the organism's characteristics and functions. In human beings, for example, genes control the color of a person's skin, eyes, and hair, his or her blood type, and all other inherited characteristics. The genes for our species come in many versions, and that genetic variety explains why human beings are not all as alike as identical twins