Wednesday, January 25, 2012

Environment and Biology: Dormancy - Hibernation and Aestivation - Survival Adaptations of Organisms

Environment and Biology: Dormancy - Hibernation and Aestivation - Survival Adaptations of Organisms
Abe V Rotor
Ant colony on the move to safe ground, sensing the coming of the rainy season.

The lichen is a classical example in the art of dormancy. The lichen shown here belongs to the foliose type. Lichens are made up of algae and a fungi living in symbiosis, which explains their superb ability to withstand extreme environmental conditions - except pollution.

Frangipani or kalachuchi remains leafless in summer, then
bursts with flowers. It regains its foliage come rainy season.

"Sleep, so called, is a thing which makes man weep,

And yet a third of life is passed in sleep."
- Lord Byron, Don Juan

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, The Little Plant, we learned in the elementary.

In the heart of a seed,
Buried deep so deep.
A tiny plant,
Lay fast asleep.
"Wake," said the sunshine,
"And creep to the light."
"Wake," said the voice,
Of the raindrops bright.
The little plant heard
And it rose to see,
What the wonderful,
Outside world might be.

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 BaƱos, the seeds of about 100,000 rice cultivars 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.

A colony of dormant Drynaria fern clings on an acacia tree.

This epiphyte, relative of the mistletoe, takes advantage over its host in its deciduous state.

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 older than that of the Great Pyramid of Giza.

Vernalization – Overwintering of Crops

Local yam or singkamas sends out shoots after a long
dormancy, which coincides with the rainy season.

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.

Fasting – Mechanism for Survival

After its fill, an iguana can fast for several days.

Hairy caterpillar prepares for final molting, enters pupal stage, and emerges into moth.

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 crocodile, 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? What made H1N1 virus (swine flu) spread into pandemic in so short a time? When will its virulence subside?

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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