- Survival Adaptations of Organisms
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
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,
Lies a little plant, lying 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.
The Myth of Rip van Winkle
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. xxx
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