Cheetahs (Acinonyx jubatus) are spotted cats best known for being the fastest land animal, sprinting at speeds of about 120 kilometers per hour (75 miles per hour). They can accelerate from 0 to 97 kilometers per hour (60 miles per hour) in three seconds, making them faster than most sports cars. Cheetahs use their acceleration and speed to chase down and catch prey, like gazelles, on the sub-Saharan savannas of Africa. Cheetahs have small heads, lean bodies, and long legs. They have a yellowish-tan coat with distinctive black spots. And they are facing extinction.
Pressure from climate change, hunting by humans, and habitat destruction are reducing the size of their populations. Cheetahs also face problems from their own genes. Cheetahs have a low rate of reproductive success, meaning that as a species they are not always able to reproduce. With fewer offspring, the population can neither grow nor adapt to changes in the environment.
Evolution of Cheetahs
There are various theories concerning cheetah evolution, but a popular one holds that cheetahs descended from the same ancestor as the American puma (Puma concolor). About 10,000 to 12,000 years ago, around the end of the last ice age, an extinction event took place that wiped out many large mammal species around the world. The wild cheetahs of North America and Europe became extinct, leaving only the Asian and African populations of cheetahs. Since then, stress from climate change, habitat loss, and human activities have put pressure on the remaining species. Today, cheetahs are found in the wild in several locations in Africa, while a tiny population of another subspecies, the Asiatic cheetah, is found in Iran. Scientists estimate that fewer than 8,000 African cheetahs are living in the wild, and there may be fewer than 50 Asian cheetahs left in the world.
Bottleneck Events
Cheetahs today are heading toward extinction. However, this is not the first time cheetahs have faced extinction. Genetic analysis of wild cheetahs shows they may have survived two historical bottleneck events. In biology, a bottleneck event occurs when something happens to sharply reduce the size of a population. When this happens, the few remaining individuals end up mating with relatives; this is called inbreeding. Inbreeding reduces the size of the gene pool, which can lead to problems such as decreased genetic variability and the persistence of potentially harmful mutations. When genetic variability is reduced in a population, it is harder for the remaining population to adapt to changes in their environment. In a very small population, any mutations that occur are much more likely to be passed on to offspring.
The first bottleneck event that cheetahs may have undergone occurred around 100,000 years ago when cheetahs expanded their range into Asia, Europe, and Africa. This range expansion is believed to have occurred rapidly, spreading cheetahs out over a very large area, thus restricting their ability to exchange genes. This bottleneck would have negatively affected the populations of cheetahs, but they were able to bounce back.
The second likely bottleneck event occurred about 10,000 to 12,000 years ago, around the end of the last ice age. The wild cheetahs of North America and Europe went extinct, leaving only the Asian and African populations. As large mammals died out across the world, the number of surviving cheetahs dwindled. This led to extreme inbreeding among cheetahs. Even though the number of living cheetahs grew to as many as 100,000 during the 19th century, their genetic variability remained low due to the extreme bottleneck event that took place thousands of years previously.
Cheetah Genes Today
Present-day cheetah populations have relatively low genetic variability, evidence for which comes from several different indicators. One way to test for the degree of inbreeding is to perform a skin graft. This involves transplanting a piece of skin from one cheetah onto another to see if the receiving cheetah accepts or rejects the graft. In inbred populations, skin grafts are easily accepted by individuals unrelated to the donor. This occurs among cheetahs, suggesting they have lost some genetic diversity. Another sign of inbreeding is asymmetrical skull development. In inbred animals, the skull is more asymmetrically shaped. A study of cheetah skulls in museum collections showed that their skulls are asymmetrical.
A third line of evidence for inbreeding comes from cheetahs’ high homozygosity. Homozygosity is a measure of the genetic similarity between individuals in a population. Cheetah genomes typically exceed 90 percent homozygosity. By contrast, domestic cats (Felis catus) and dogs (canis lupus familiaris), while also commonly inbred, have significantly lower rates of homozygosity.
Cheetahs are facing different threats that are collectively pushing them toward extinction. Humans are threatening the population by infringing on their habitats, hunting them, and perpetuating climate change. Experts believe cheetahs may also suffer from infectious diseases spread by domestic cats. Cheetahs are unable to cope with these pressures in part because they lack the genetic variability to respond to these pressures. Evidence suggests cheetahs have faced genetic bottlenecks in the past and survived. As the population of wild cheetahs dwindles, only time will tell if it can survive the current genetic bottleneck.
