Camels have an incredible ability to survive weeks without taking even a sip of water. Now, we have a better idea of the secret ingredient that helps their bodies achieve this.

We already know that to save every drop of liquid, camels have a host of biological tricks – including large and intricate noses that grab at the water in the air leaving their bodies and modified blood that can withstand dehydration.

They can gulp down hundreds of liters in a matter of minutes when water is available, which they then only absorb slowly to avoid osmotic shock; additionally, their body temperature fluctuates from 31 to 41 °C (87 to 105 °F) to reduce sweating.

When a human runs low on water, our kidneys shift gears to preserve as much moisture as they can. Water is filtered into tubules in an area called the cortex, where it flows into another part called the medulla. Here, ions from dissolved salt are pumped across membranes to create an imbalance that forces a portion of the water to return to the blood, with the rest carrying away waste as urine.

Camels' bodies take this water re-uptake to the extreme, concentrating their urine to a degree we could never manage. In a huge study examining genes expressed in the cells of Arabian camels' (Camelus dromedarius) kidneys, a team of researchers compared those from camels that were dehydrated and camels who'd recently had their fill of water.

"We identified hundreds of genes and proteins that are significantly changed in both kidney cortex and medulla in dehydrated and rehydrated animals compared to controls," said University of Bristol animal physiologist Fernando Alvira Iraizoz.

Many of the genes that changed expression in dehydrated camels appeared to be involved in suppressing the fatty substance cholesterol in their kidney cells.

So, Alvira Iraizoz and colleagues measured the amount of cholesterol in kidney plasma membranes in the dehydrated animals and compared it to the controls. They found dehydrated camels did indeed have less cholesterol in these kidney cell membranes than hydrated ones.

What's more, genes coding for transporting ions and water channels across the cell membranes were also being expressed more in the dehydrated camels' kidney cells. Together, these findings support the team's hunch that dehydration-induced cholesterol suppression allows camels to cling onto more water in their kidneys.

"A decrease in the amount of cholesterol in the membrane of kidney cells would facilitate the movement of solutes and water across different sections of the kidney – a process that is required to efficiently reabsorb water and produce a highly concentrated urine, thus avoiding water loss," explained Alvira Iraizoz and molecular neuroendocrinologist Benjamin Gillard, also from the University of Bristol.

In our rapidly warming world, livestock animals that can endure harsh conditions are becoming ever more important. The Arabian camel already supports millions of people since its domestication over 3,000 years ago. They provide milk, meat, clothing, transport, and shelter in several arid parts of our planet.

"[Multiomic studies] provide very valuable information in the context of desertification and climate change and could be used to evaluate how different species will adapt to their already changing environments," said Alvira Iraizoz.

The researchers are now working on a similar analysis of the camel's brain, and they plan on looking into the genetic expression response to severe dehydration in other arid mammals, like the adorable hopping rodents called jerboa.

This research was published in Communications Biology.