The other day I posted a Science Factoid on the Science@home fanpage on Facebook, saying that around 10,000 years ago the cheetah population had gone through a bottleneck and had got down to less than 7 individuals. This prompted a bit of discussion, which led to this post on “Interesting Facts About Cheetahs.” Thanks to Jessica who started it.
Why less than 7 individuals?
Cheetahs are extremely inbred – as inbred as lab rats. They can actually take skin grafts from each other, most animals can only take skin grafts from themselves. It’s been shown that 7 individuals of a population will still have 95% of the genetic variability – so if you look around you at 7 people they will be tall, short, blonde, brown-eyed, etc. To have as little variability as cheetahs now have, there would have had to be less than 7. Or I suppose they could have been very closely related and not variable.
Why 10,000 years ago?
We don’t really know, we can’t date it that closely. Some work has been done on human genetics to let us date things, but there’s been a lot more work on people than on cheetahs! Some day maybe. What we do know, however, is that around 10,000 years ago a lot of animals around the world died out. It even has a name, the great “Post-Pleistocene size reduction,” because most of the animals that died were the megafauna – the mammoths, cave lions, giant kangaroos, and diprotodons (giant wombats). It probably had to do with the end of the ice age – when it’s cold animals tend to be bigger but in warm conditions they’re generally smaller. This is because large animals are more efficient at staying warm, they have a large body (volume) to generate heat and a relatively small skin (surface area) to lose it.
There are quite a few fossil cheetahs from Europe and the Americas going back over 2 million years. These are definitely not modern cheetahs, but they have a similar build and so probably a similar way of living. Both modern cheetahs and some of the American fossils are related to pumas, an American cat. So the cheetah could have developed in the America’s and moved to Africa and Asia through Europe, or it could have developed in Europe then some moved to America as pumas.
There are fossils found in Europe from the ice age of a giant cheetah, about the same size as a lion but not as bulky. Other than size it is very similar to modern cheetahs and may even be the same species – lots of animals are bigger when it’s cold.
Cheetahs are definitely cats, but they have some unique features. All the smaller cats including cheetahs and some other animals purr, but great cats don’t. Instead they roar, which needs a different form of the larynx. Cheetahs do, however, have round pupils like the great cats rather than slit pupils like small cats. None of these fossilise, but we can work out the timing of some of the splits. This is only one possible scenario. I don’t know enough about cat anatomy to be definitive, it’s an illustration. At some point there must have been a common ancestor (Granny Felix) who probably purred and had round eyes. From this ancestor came two lineages, one that had round eyes (Uncle Max) and one that developed slit eyes (Aunt Minnie). The round eyed lineage then split again into one that purred (Cousin Kwik) and another that started roaring (Cousin Magnus). Of course this is complicated because there are far more than two features in the cat family tree, but it’s a very simple explanation of how biologists work out family trees.
Cheetahs are the fastest animals in the world and most of their body is adapted for speed. Their claws don’t retract to give them better grip, they have the same ligaments as other cats but they are weaker. Their dewclaw (thumb) is shorter and straighter and helps them catch prey. When they catch up to the animal they are chasing the dewclaw can rip along it’s side and slow it down or trip it up. Their chest is deep and they have large nostrils to allow them to get as much oxygen as possible during their sprints. Their spine is extremely flexible and acts as a spring, storing energy from landing that can then be used to push off on the next leap. Finally their relatively long legs allow more muscle movement and also act as levers, converting small contractions into large movement on the ground.
There is great difficulty breeding cheetahs in captivity, although many zoos are trying to because they are highly endangered. Part of the problem is their extreme level of inbreeding, cubs often have problems with their spine or legs and they are very susceptible to disease. Females are extremely choosy, so zoos need several males for them to select from. Females ovulate at irregular times, it has just been discovered that this is because ovulation is triggered by hearing a particular barking call from males! Plus the male penis (like all cats) has backward pointing spines on it that rip at the female’s vagina during mating, stimulating her to produce pregnancy hormones. So you can see that artificial insemination is hard! Zoos are getting progressively better at breeding cheetahs, but because they are so inbred it isn’t clear whether they will ever be viable as a wild species or whether they would naturally be dying out, even without human interference.
So cheetahs are beautiful, and beautifully adapted animals. They are also a fascinating study in evolution and natural ecology.
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