Biologist and physicians are trying to understand what kind of molecular mechanisms organisms are using to cope with dehydration in order to continue their lives.
Humans are incapable of preserving themselves by shutting down their metabolism completely. Human energy reserves can last for up to 70 days. Our ability to withstand life without water can vary between 1-10 days. In fact, when people suffer long term dehydration and hunger, they experience gastro-intestinal problems after they resume nutrient intake. However this is not the case for other organisms. There are interesting examples regarding this issue:
Easter pygmy possum
The eastern pygmy possum, Cercartetus nanus, one of the marsupials living in Southeast Australia, is a small mouse-like animal which sleeps during the day and hunts at night. They weigh about 15-45 grams and have a length around 7-11 cm. They live in an environment known for its irregular climate, sometimes receiving abundant nutrients, sometimes receiving scarce. This small creature takes advantage of the plentiful days and stores fat. They can hibernate up to 310 days by utilizing this reserve very carefully. That is why it holds the record for the longest hibernating organism among mammals! Another species belonging to the same genus lives in Tasmania (average length 6.4 cm, height 7 grams) however it only remains in hibernation for a maximum of 6 months. Both species live off eating insects, pollens and nectar.
The ground squirrel
The ground squirrel (Spermophilus parryii) of the Arctic tundra near the region of Alaska takes energy conservation very seriously. During hibernation, this organism can lower its body temperature from 37 °C to -2.8 °C. On the other hand, the American black bear (Ursus americanus) shivers in its spot in order to keep its body temperature at a normal level. A frog living in Australia with yellowish-green stripes on the back (Litoria alboguttata) can sleep up to five years without food and water in times of drought. This frog – obviously inspired from a reliable source of knowledge – digs a tunnel underground and covers itself with a tiny film of dirt in order to reduce the negative effects of the drought. It also slows down its metabolism by carefully consuming energy reserves to adjust itself for the food shortages and the drought. Frogs resurface with the start of the rainy season and begin their feeding frenzy. They can even eat organisms half their size since they will need the energy for reproduction.
One of the typical examples of energy conserving animals is the fat-tailed dwarf (grey mouse) lemur (Microcebus murinus). This animal inhabits the dense forests of Madagascar and surrounding islands. It spends the day resting on tree branches and is active during the night. They hibernate up to seven months in hollow logs by pulling in their legs towards their abdomen. During this episode of their lives, they survive by consuming the fat reserves in their tail. They adjust their body to the ambient temperature just like reptiles to conserve energy. Body temperature therefore fluctuates depending on the weather in logs with poor insulation. However it is relatively stable in well insulated logs.
Malaysian night moth
Another amazing example is the local Malaysian night moth, Attacus atlas. Caterpillars of this species do consume a lot of food whereas adults do not eat anything. The mouth structure of this particular moth and other moths do not develop as much in adult form. Therefore, these moths must rely on larval fat storage and eventually die in two to three weeks when they run out of reserves.
Another example is the Bar-tailed godwit (Limosa lapponica). The Alaskan version of this bird migrates amazing distances without a break. It does not eat anything during flight, almost flying 7000 miles with one tank of gas. In one study, it was observed that a female bird left the nest in Western Alaska and without feeding in eight days, flew 7257 miles and arrived in New Zealand. Also observable is that these female birds, as a work of Divine mercy, experience a reduction in their digestive organs and convert half their body weight into fat before undertaking such flights.
European land snail
The European land snail, Helix pomatia, is another typical example of this phenomenon. These creatures lock themselves into their shells for days and weeks during seasons of long drought and cold. They secrete special mucus to seal the shell as soon as they pull themselves in. This mucus film slows water loss caused by evaporation. They reduce metabolic activities to conserve energy. Snails pop back out of their shells upon the arrival of warmer weather or water.
African gilled lung fish
The next example is the African gilled lungfish (Protopterus amphibius). This fish both possess gills and lungs and also conserves energy by a substantial reduction in its physical activity. It buries itself in a river or lake bed by digging tunnels. It secretes a protective mucus layer when water levels drop. This way it can withstand starvation for almost two years.
The python is another animal also resistant to starvation. This snake, which can swallow animals as big as their size, or even bigger, shrinks its digestive organs when there is scarcity of food, and can survive up to a year and a half without eating. Apart from other animals and humans, their digestive system only functions when they consume their prey. Their intestines swell almost twice as much within 24 hours when they start eating. It shrinks back to its original size upon completion of digestion.
The final example regarding this topic is the emperor penguin (Aptenodytes forsteri). Male penguins face starvation for up to four months because of paternal care and compassion. New chicks hatch into a -76°C world because breeding season coincides with the Antarctic winter. After laying their eggs, the female penguins leave the task of incubation to their male partners and depart towards the ocean to bolster their food and nourishment intake after laying eggs. Male penguins left in charge of incubation take care of the eggs inside skin folds and maintain the incubation temperature during this time without any food intake. Tasks are once again exchanged upon the arrival of the mother penguin and this time the male penguins head out for nourishment.
The sustenance of life in a majority of the species of animal kingdom depends on the sensitive balance between times of starvation and nourishment. In times of shortage and hunger, the trick to survival depends on how energy is utilized efficiently. If an organism successfully manages its hunger in the best way possible, the greater chance it has for survival. For life is built upon the principle of conservation and balance, and God-given equipment with various mechanisms for living things to be protected in harsh times of famine, drought and shortages. Animals can feel the changing conditions when nutrients increase or decrease in availability and develop behaviors accordingly, maintaining a life style adapted for these periods.
If we can analyze how these organisms that are adapted to starvation can switch into a long term stagnant life style and regulate their metabolisms under harsh conditions, maybe we humans can, too, develop treatments one day that will enable us to turn our metabolism on and off like a thermostat. Furthermore, molecular treatments that control weight loss and gain can also be developed. Survival methods in extremely hot and cold conditions could be put forth with some inspiration from the living world.
"The Superstarvers." Zoology. Scienceillustrated.com. July-August 2010, pp. 60-66.