Desiccation’s What You Need

Have you been enjoying the summer? Sky high temperatures, paddling in the sea and relaxing with an ice cream, we’re finally able to enjoy the outdoors again after a very long winter.

But the heat has its dangers. Most of us suffer a little sunburn, but every year the news also carries stories of dogs cooking in closed cars, and even people dying from exposure.

Once temperatures reach over 55oC it becomes difficult for humans and most mammals to survive, and without water or shade they will die after a few hours. However, some animals have evolved to cope with extreme heat and thrive where others would die.

Imperial Camel Corps Brigade with the Egyptian town of Magdhaba in the distance, 23 December 1916. (wikimedia commons)
Imperial Camel Corps Brigade with the Egyptian town of Magdhaba in the distance, 23 December 1916. (Wikimedia commons)

Probably the most well known animal to have evolved to survive in desert environments is the camel. Camels have a number of adaptations which allow them to survive long periods of drought and high heat. The most obvious of these adaptations is the hump. Originally the hump was thought to be a reservoir of water, but it is actually a large fat store. This fat does hold water in the tissue, but its main purpose is as a food source during long treks over the desert. However the hump also works to cool the animal by keeping fat stores away from the rest of the camel’s body, removing the insulation from the other tissues and allowing more heat loss. The camel’s blood is also adapted to aid in survival: oval red blood cells allow better blood flow during dehydration, and also allow the blood to take up much more water. This enables the camel to drink more than 100 litres of water in one sitting. Combined with many other features of their physiology they are perfectly adapted to survive the desert heat.

Camel Skull
Camel Skull

Most of the adaptations in the camel are there to either reduce water loss or allow the animal to survive when dangerous amounts of water have been lost. In all living creatures water conservation is their main concern in high temperatures. Very different methods for conserving water are seen in one of the most successful desert occupants: the scorpion. Scorpions were the first arthropods to occupy terrestrial environments and are today found on every continent except Antarctica. Their extremely adaptable body has enabled them to survive in almost all land environments except the tundra. Desert species of scorpion have adapted to their environment both in behaviour and physically in order to maintain water.

Scorpion
Scorpion

The simplest way for scorpions to maintain water is to remain in cover during the day. Although capable of surviving temperatures ranging from -20 to over 65Oc tests have shown that there is a significant increase in mortality when individuals are exposed to temperatures of 40Oc and above for more than six hours. Lab experiments also show that the carapace of the scorpion is very effective at reducing water loss below 35Oc. By operating at night they keep to a temperature range which prevents excessive dehydration allowing them to replenish water loss from their prey instead of having to find water in the desert.

The lack of prey in the desert, and food being the only source of replenishing water, also help to explain the potent venom found in some desert scorpions. While most scorpions around the world are not dangerous (often no worse than a bee sting) those such as the deathstalker (found in the deserts of North Africa and the Middle East) have venom capable of killing a weaker human. While it is a potent defence, its main purpose is to kill prey quickly before it can get too far away from the scorpion.

UV Scorpion
UV Scorpion
Scorpion
Scorpion

The hard shell of the scorpion also has another, more unusual property. It glows blue-green under ultraviolet light. It is not yet fully understood why this happens, but a popular recent theory is that the reaction to UV light acts as warning to the scorpion that there is too much light and they are more visible to predators. This fluorescence can be seen in one of the interactives at the new ‘Into the Blue’ exhibition at Hove Museum.

Waterbear (Tardigrade) from the drainage of a hot spring in Lassen County, California  (wikimedia commons)
Waterbear (Tardigrade) from the drainage of a hot spring in Lassen County, California (Wikimedia commons)

While both of the animals mentioned above have evolved to suit their environments magnificently, they both pale in comparison to the hardiest animal on earth. Tardigrades, or water bears, are found from the poles to deserts, and live both in the water and on land. These tiny animals measure less than 1mm in length and require water in order to operate normally, needing at least a film of water over their bodies when on land. However, when this water dries up, tardigrades are able to enter a state of suspended animation known as cryptobiosis. In this state all but the most essential life processes shut down, enabling the animal to freeze or dry out. In cryptobiosis the tardigrades are able to survive on as little as 1% of the water their bodies normally hold. They can stay in this state for years until re-exposed to water.

Adult Tardigrade (wikimedia commons)
Adult Tardigrade (Wikimedia commons)

These capabilities allow tardigrades to survive in the most inhospitable environment currently explored by mankind – space! Tests by the ESA and NASA have shown that tardigrades are able to survive the vacuum of space, sub zero temperatures and some even survived cosmic radiation. The hope is that by studying tardigrades, technologies can be produced to help us in our exploration of space.

Lee Ismail, Curator of Natural Sciences

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