Found across large swaths of Africa and parts of Iran, the cheetah can reach top speeds of up to 121 kilometers per hour (75 miles per hour), meaning it is undoubtedly the fastest land animal. Despite its fearsome reputation, a new study published in the journal Genome Biology reveals that this incredible predator has had a difficult past, having lost most of its genetic variation over the last 100,000 years as it migrated out of North America.
The cheetah, Acinonyx jubatus, evolved around 5.5 million years ago, about 5 million years before anatomically modern humans evolved. Researchers from St. Petersburg State University decided to investigate its relatively unknown ancient migratory history by looking at the genetic history of the animal. To do this, they enlisted the aid of a cheetah called Chewbaaka, along with six other wild cheetahs from Namibia and Tanzania.
Evolution is marked by the appearance of a new species from an old one; this process is known as speciation. As speciation is driven by genetic changes, the evolution of a species’ lineage can be determined by tracking the changes in the frequency of genes over time.
To this effect, the genome of the modern cheetah was sequenced using genetic material extracted from these seven big cats. This genetic record was compared with the genetic information that could be extracted from various fossilized remains of ancestral cheetah family members across the world, particularly those from North America.
As suspected, the cheetah is descended from a relative of the American puma; their family history is spread over North and South America, Europe and Asia. The species appears to have suffered from two “bottlenecks” – periods of time when the genetic variation in the lineage was significantly reduced. Normally, a huge decrease in genetic variation indicates a major population decrease.
The first took place 100,000 years ago, during the end of the Pleistocene – a cold geological period known for frequent spikes in glacier formation. The fossil evidence at this point indicates that cheetahs moved from North America towards Asia before making their way south to Africa, during which populations began to dwindle. Small, related groups of cheetahs stuck close together in otherwise huge territorial spaces of up to 2,072 square kilometers (800 square miles), which encouraged highly damaging incestuous mating.
A second bottleneck occurred around 12,000 years ago, right at the end of the last glacial maximum. This period of relatively quick climate change coincided with another population drop, mainly in the original population group in North America.
In addition, 18 cheetah genes were found to have experienced very damaging mutations. In particular, a gene called AKAP4 showed a high mutation frequency, which may have caused sperm to become defective; the protein generated by this gene is an important piece of the sperm's tail. The cheetah, despite being a prolific breeder, has poor reproductive success, with up to 90 percent of the offspring dying before reaching adulthood. This defective gene may be contributing to this.
All in all, the genetic variation of the modern cheetah is incredibly low, even worse than observed in populations of inbreeding dogs or cats. The researchers note that up to 99 percent of its genetic variation has been lost over time.
