Wednesday, October 10, 2012

Part 1 - Species Survival through Hibernation and Aestivation

Dr Abe V Rotor

                                  Sleep, so called, is a thing which makes man weep,
                                              And yet a third of life is passed in sleep.

                                                            - Lord Byron, Don Juan

Cotton Stainers mating.  Reproduction is the ultimate aim of many short-live organisms.  They die at the onset of the cold months, others in the dry summer. 

Nest of Green Tree Ants.  The life cycle of the ant colony 
jibes with the deciduous nature of the host tree.  
    Who is not fascinated by the first heavy rain in May, the start of the monsoon season or habagat? The fields come alive, transformed from scorched landscape into vast greenery. What brings about this sudden transformation?

     Rainwater breaks the dormancy of seeds lying in the ground. It wakes up the sleeping little plant in a poem we learned in the elementary, which starts with these lines.

“In the heart of a seed buried deep so deep,
… a little plant lies fast asleep.”

      Seeds of many annual plants like saluyot (Corchorus olitorius) and wild Amaranthus wake up to the rain. The same stimulus touches dormant buds like a magic wand, and in a short time become new and fresh crowns of trees that had been in deciduous state. Tubers and corms come alive simultaneously with tillers and stolons and take their first peep above ground. Bulbs send out their first shoots.  There is rejuvenation everywhere.

     Thunder and lightning accompany rain and send old folks to hunt for mushrooms the day after. There is scientific explanation to this, although much of the mystery remains.  Lightning directly fixes atmospheric nitrogen into nitrate (NO3), which being soluble, is brought down by rain. It is then absorbed by plants, protists - and fungi to which mushrooms belong. How is dormancy of fungi explained?  Is it the same as in green plants?

     Basically, it is.  While plants photosynthesize their food in the presence of sunlight, fungi on the other hand are saprophytic, and draw energy from decomposition of organic matter. But the conditions that break dormancy is the same – the supply of nitrates and other nutrients, sufficient water, suitable foothold and substrate, and favorable temperature. The mycelia of fungi which appear as white, threadlike mass may remain dormant, then springs to life, rapidly spreading all over its growing medium until it is time to produce fruiting bodies, which are the mushrooms.   

                                                       Dormancy of Seeds

     Seeds are masters of the art of dormancy – the temporary stoppage of life processes. Nature has precisely made dormancy as a means of adaptation, and adaptation is a means of survival.  Adaptation is the key to fitness defined in Charles Darwin’s law of natural selection. The failure of seeds to grow immediately after maturity – even though conditions of the environment may be favorable – is generally an advantage of many plants.
     This phenomenon is demonstrated by plants which are highly sensitive to photoperiodism.  These are classified as short-day and long-day species and varieties. For example, the traditional rice variety, wagwag, produces grains only during the short-day period, usually in the last quarter. If it is planted late and does not have chance to mature within the period, it will remain in its vegetable stage and will flower only in October in the following year.

     Many desert plants exhibit superb resistance to punishing heat and dryness.  They produce seeds that lay dormant in the hot desert soil for as long as there is no rain. Then, when rain finally comes, these seeds sprout immediately, grow and mature as fast as water in the soil is lost.  Before the desert reverts to its arid condition, the plants have completed their life cycle, and their seeds once more lie dormant waiting as long as they could for the next unpredictable rain.

     Many seeds of cereals and other annual remain dormant for a few days to some weeks under natural condition. However at the International Rice Research Institute (IRRI) in Los Baños, the seeds of more than 80,000 rice varieties kept in the institute’s Germplasm Bank can remain viable for 20 years. It is necessary to germinate the seeds before they lose viability to replace the gene collection.

     Most farm crop seeds are probably dead after 25 years, even under favorable storage conditions.  The alleged germination of seeds after prolonged storage in ancient tombs is known to be a myth.  I had a chance to examine some authentic seeds recovered from a pharaoh’s tomb at the Egyptian Museum in Cairo.  The seeds were highly carbonized and have completely lost their viability.  There are however, seeds of some plants in the wild that retain their vitality for 50 years or more. Dry arctic lupine seeds found buried in lemming burrows under 10 to 20 feet of frozen soil in the Yukon Territory in Canada, were able to germinate.  Their assumed age is about 14,000 years.

Vernalization – Overwintering of Crops

     The term vernalization was first introduced by my professor in Plant Physiology in the late fifties. The technology had just began to revolutionize farming in countries where winter is long and harsh. Formerly in these areas, it was almost impossible to grow wheat and other crops because of the very short growing season. Even if planting is done in early spring, by the time the grains start to mature, frost has already set in.  
     The Russians found out that by pre-germinating wheat seeds and keeping them safe and healthy during the long winter, the young seedlings will resume growth immediately as the snow thaws.  Much time is saved for the crop to grow, while its life cycle is significantly shortened.  Before the winter sets in, the crop is already harvested.

     Thousands of hectares have been placed under cultivation following this procedure. Seeds of wheat, oats and barley are planted in late autumn. They germinate and remain dormant under snow for the whole winter (overwintering), then resume growth in spring and harvested at the end of the short summer. Researches on the application of vernalization have successfully made  other crops adapted to this kind of environment. Former wastelands in Siberia and Northern Canada are now productive farmlands.  

 Breaking the Dormancy of Wildlife Species

     Aestivating snails, crustaceans and frogs ensconced in the bottom of rice fields are similarly liberated by the monsoon rains. Together with hito and dalag which aestivate in mud like the lungfish, they stir with the first contact with rain water, wiggling out to freedom in the flooded fields where they resume active life – growing, mating and reproducing – and migrating while the monsoon persists and whole fields are one contiguous lake.

      These are biological feats that feed man’s fantasy to live long and postpone death.
1.      The African lungfish buries in mud up to two feet deep in order to escape extreme drought and heat in the desert.  It curls into a ball and seals its chamber with its own mucus secretion and there it aestivates for as long as four years in the absence of rain.

2.      Garter snakes survive the long Canadian winter while remaining in burrows, or in extreme cases, encrust in ice.  They are liberated only when the ice thaws in spring, and soon resume their normal activities.  They grow, mate and reproduce before they hibernate again come next winter.

3.      Snakes and other reptiles easily go for long periods without food.  Snakes have been kept alive without food for almost two years. A python in captivity has been observed to go without food for a period of 13 months. Frogs can fast for 16 months and fishes for 20 months; land tortoise for a year and salamander for one and one-half years.

4.      The most popular mammals that hibernate is the bear.  Sustained by large amounts of stored fat, it sleeps in the entire winter in its den. Its normal body temperature remains the same in spite of its heartbeat  reduced from 40 to 10 times per minute. Beware, a sleeping bear may be provoked at the slightest disturbance.

5.      Bats in hibernation hang in caves, eat nothing, their hearts feebly beating and their breathing scarcely imperceptible. Through collective body heat the colony survives extreme cold and long winter.    

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