Where do jerboas have long legs?

Jerboas are similar to a hybrid of a mouse and a kangaroo: a mouse muzzle, front legs and body sit on the longest hind legs, and a long “kangaroo” tail dangles from behind. On these hind legs, jerboas jump across deserts and semi-deserts, keeping balance with the help of their tail. Jumping on hot ground or sand is easier than mincing on the same sand on all four legs, so the “kangaroo” nature of jerboas can be seen as an adaptation to difficult habitats. (As well as the non-mouse-like large ears in many species – they help the jerboa to cool down, remove heat from the body.)

But any evolutionary change is primarily a change in genes. Long legs appeared in jerboas because, in the course of natural selection, it was easiest to survive for those individuals in whom genes did not work like in other rodents. What exactly are these genes, tried to find out the employees of the University of California at San Diego and other scientific centers. They compared the genetic activity in the Egyptian jerboa and the common house mouse, whose evolutionary paths diverged about 55 million years ago. The gene activity in both was compared not from top to bottom, but in the cartilaginous cells of the forming paws, front and back. Maybe jerboas and mice have genes in their front legs that work differently, but they don’t affect the size of the limbs; these differences had to be weeded out as unnecessary.

In the end, as stated in the article in Current Biology, the researchers had in their hands a list of as many as 1,755 genes that, to one degree or another, are responsible for the differences between the hind legs in jerboas and the hind legs in mice. Such a huge number is due to the fact that genes do not work in a vacuum, they are connected with each other, affect each other, and if one changes its activity, then a dozen or two more change activity after it.

However, some genes for jerboa legs are clearly more important than others. For example, gene shox2which works in jerboas but doesn’t work in mice. Shox2 encodes one of the transcription factors – the so-called proteins that control the activity of other genes. With genome shox2 one of the signs of a complex genetic disease called Shereshevsky-Turner syndrome is associated. People with Shereshevsky-Turner syndrome are characterized by, among other things, short stature and disproportionate development of the limbs, which are associated precisely with anomalies in shox2… There are also a number of genes that stop bone growth in mice, but in the hind legs of jerboas, these genes are tuned to make bones grow longer.

One way or another, the results obtained clearly show that such a seemingly simple and obvious trait as the length of the legs depends on a whole network of hundreds and thousands of genes – let alone more complex and less obvious things, like immunity or brain architecture.

Source: Автономная некоммерческая организация "Редакция журнала «Наука и жизнь»" by www.nkj.ru.

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