Wednesday, October 10, 2012

Part 2 - Hibernation and Aestivation: The Myth of Rip van Winkle

 Dr Abe V Rotor
Bivalves prepare for dormancy as the water recedes. 
They stay buried deep in the mud even as the outside 
condition is harsh.  Rain will liberate them and resume
the life functions.     
    
Reproduction is nature's gift of seasonal organisms.  
Their progeny carry on their genes. 


House sparrows have learned to live with man wherever he settles down, 
but will not submit themselves to domestication like the dog and the cat.


Algae, lichens, mosses and liverworts "dry" in summer, and 
resume growth and reproduction when favorable conditions return. 

     The story of Rip van Winkle, the man who slept for twenty long years, may be better remembered for its sociological, rather than its biological significance. Rip found solace on some mountaintop and there he fell into deep slumber.  When he woke up he was a very old man.  The way   Washington Irving, the author described him must be true. Of course, it is only fiction, but it raises the question, “Do we really preserve youthfulness in sleep?” What really happens in prolonged sleep?

     We know that life processes slow down when we are asleep, and in the process our body gets the needed rest.  When we wake up we feel recharged. Surely sleeping is still the best way to be fit and healthy - and young, too.

     But his is not the case of Rip van Winkle, or that of Sleeping Beauty, the beautiful maid who remained asleep until “a prince came and woke her with a kiss.”  These cases point out to the similarity of prolonged sleeping with coma.  The body operates at low metabolism, but gets no replenishment. After the reserve fat is exhausted, the only source of energy are the muscles and other connective tissues.  It is no wonder a bear emerges from hibernation weak and hungry. 
The Virus that Sleeps for 20 Years

      One of the wonders of biology is the virus. The tobacco mosaic virus, Marmor tabaci, for one, can remain dormant for as long as twenty years even if the tobacco leaves are subjected to flue-curing and re-drying.  The virus remains in the cigar or cigarette, so that a smoker can transmit it unknowingly to a living tobacco plant by mere contact. Unlike obligate parasites which can not survive outside of their hosts, the virus may remain as an infective particle after its host is dead or gone. 

     The virus wakes up once it is inside a living host.  By dictating the host, the latter multiplies the virus.  Now in countless numbers, the virus spreads throughout the plant.  The infected plant, in turn, infects nearby plants and threatens to spread throughout the whole field. Like other viruses that infect animals or other plants, tobacco mosaic virus may cause an epidemic. The seriousness of the disease in the farming community can only be imagined since it is capable of infecting other crops that include those belonging to the same family, Solanaceae, to which tomato, pepper, eggplant and Irish potato are members.

     Is the virus then, a living thing?  Scientists look at it differently from true living things because it lacks the vital processes of life. It is not recognized to belong to any of the sub-kingdoms of the biological world.  As a chemical particle however, it is endowed with the same universal property of living things, Deoxyribose Nucleic Acid or DNA.  It is this code of life that it uses as a tool in communicating with a host cell once it has gained entry. The host cell then decodes the virus’ DNA messages. Thus it is the host that actually duplicates the virus because the latter can not reproduce by itself alone.

The Physiology of Hibernation
 
      To hibernate is to pass winter in a suspended, dormant, or torpid condition.  In this state of lethargy, organisms have a better change to survive cold and food shortage. During hibernation metabolic activity is greatly reduced and body temperature is lowered. A hibernating mammal spends most of the winter in a state close to death; in fact the animal may appear to be dead. Some have body temperature close to that of freezing; respiration is brought down to only a few breaths per minute; and the heartbeat is so slow and gradual as to be barely perceptible.  Among mammals, true hibernators are found in the Orders of Chiroptera (bats), Insectivora (hedgehogs), and Rodentia (ground squirrels). There are mammal hibernator that do not only rely on reserve body fat.  At intervals of several weeks the animal elevates its body temperature, awakens, moves about, feeds, and then returns to its state of torpor.

      Cold-blooded animals hibernate, too. The largest is the North American Alligator which hibernates very much like frogs. Frogs burrow in mud and exists for months in their sun baked chambers.
Aestivation

      Aestivation is the counterpart of hibernation in the tropics, or where high temperature and dryness characterize the environment. The physiology involved is also the reduction of metabolic rate while the organism is protected from the harsh environment.   Aestivation also applies to plants and animals, and also among protists. These are examples of animals that are known to aestivate.

1.      Crocodiles dig into the mud and remain there virtually lifeless.

2.      South American alligators bury themselves in mud while the earth above them is baked into a hard crust.

3.      Certain Australian frogs become distended with water during the wet season and use this stored water during the aestivating period.

4.      Small mammals like the aardvark and some lemurs are not known to aestivate but undergo periods of quiescence.

5.      The Australian snails plug the mouth of their shell with a morsel of clay before entering upon the period of aestivation. Land snails secrete several diaphragms across the opening of their shells which protect them from desiccation and enemies.

6.      The African snail (Helix desertorum) and the California desert snail (Helix veatchii) may remain in aestivation for as long as five and six years, respectively.

7.      Slugs bury themselves in the ground in the season and emerge on the arrival of rain.

8.      Bivalve mollusks dig into the mud, thus they can survive in pools and patches of water.

9.      Nymphs of dragonfly which are normally aquatic may be forced to aestivate on dry land.

10.  Opposite to aestivation the Egyptian jerboa is so closely adapted to dry conditions of the desert that rain and damp atmosphere induce it to pass into a dormant condition.

Unique characteristics of organisms that under dormancy

      For both cases of hibernation and aestivation, these are the general conditions that scientists have observed among organisms that are undergoing either state.

1.      Organisms in dormancy, especially large animals, fast during the period.

2.      There is a certain stage or stages a certain organisms can remain dormant.

3.      There is a reduction in metabolic rate. Heartbeat slows down. There is a reduction in body temperature among warm-blooded animals.

4.      Reserve food is used during dormancy. As a general rule, cold-blooded animals have more food reserve and that they use it more economically than do warm-blooded animals.

5.      Survival time without food is usually greater among cold-blooded than among warm-blooded animals, since the former do not “burn fuel” in order to maintain a high body temperature. 
Fasting – A Third Adaptive Mechanism

     Fasting is a means of meeting exigencies of life.  It is one of nature’s best methods of dealing with physiological problems. Take the hibernating bear, the aestivating alligator, the sick elephant, the wounded dog – these fast in order to meet the problems before them. Fasting is indeed a very useful means of adaptation.

     But how long can animals abstain from food?  Let us look into these  examples.

1.      There were dogs that remained alive for 38 days without food.  The  longest survival record is 117 days.

2.      Rats may survive after 5 to 6 days. Guinea pigs may last for 7 to 8 days without food, while rabbits can live for 15 days under strict fasting.

3.      Spiders undergo incredible fasting, spinning webs daily from substances generated by their bodies. Spiders have been observed to exist without food for 17 months.

4.      Unicellular organisms such as amoebae and paramecia can exist without food from 4 to 24 days.  As a result they undergo diminution in size.

5.      The larvae of a beetle, Trogoderma tarsale, that infest cereals can live for as long as five years without food.

6.      The condor, like all other vultures, is capable of fasting for days. It gorges itself however, when it finds food.

7.      Scorpions are known to have starved for 368 days.

8.      A freshwater fish, Amia calva, can fast for 20 months.

9.      Ticks can exist in an active state for as long as four years without eating anything.

10.  A boa constrictor may remain inactive for months after a full meal. So  with the anaconda in the Amazon jungle.

Deeper mystery shrouds our knowledge of Dormancy
    
     It is practice to irradiate potato and onion before they are stored in order to retard sprouting. If radiation does not kill the embryo how does it induce dormancy? 
 
     Locusts may suddenly group and coalesce into a swarm. Like birds and other animals, migration is an adaptive mechanism to escape extreme conditions of the environment. Are these organisms not equipped with the gene for dormancy?

     Deciduousness (complete shedding of leaves) of certain trees like the narra, occurs periodically but not necessarily jibed with the dormancy period.  In fact some trees are even more luxuriant when other plants are dormant. We have little knowledge about the biological clock that dictates dormancy among different species of organisms. 

   Episodes of the Red Tide phenomenon caused by dinoflagellates, such as Pyrodinium, Peridinium, and Gonyaulax, are unpredictable. What predispose these organisms to bloom?  How do they stay dormant in between seasons of occurrence? 

     This leads us to the epidemic cycles of certain human diseases.  How do influenza viruses stay “alive” during off-season? How does HIV remain passive in an HIV positive patient?  Bubonic plague devastated medieval Europe in three major waves killing one-third of the population. How do we explain alternate virulence and dormancy of the causal organism? 

     What really induce flowering?  How does potassium nitrate induce flowering of mango during off-season? Why is it that old folk cut notches on the trunk of trees that are “lazy” to bloom?  Then for whatever reason, the wounded trees come alive with flowers and fruits.

     As I was writing this article, some birds came flying by and perched on a nearby talisay tree singing melodious songs that herald a new season -  amihan.  The Siberian winds have arrived. In the Northern hemisphere it is time for hibernation, in the South hemisphere it is aestivation. For many birds and animals, it is time for migration. 

     Except for humans, all living things take heed of Nature’s call.

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