STRATEGIC ADAPTATIONS IN PLANTS

It is not only the animals, but the plants too have acquired the unique adaptations for survival under different environmental conditions and thus, become responsible for constituting a unique vegetation or flora of a particular biome say for example, some plants have evolved to tolerate wide range of light regimes, while others have evolved to survive under extremely dry conditions, high temperature, water-saturated conditions or under saline environments and so on. Few of such adaptations may be discussed as below:

• Plant Adaptations to light regimes:
• Not only individual plants but also plant communities show adaptations to different intensities of light. Plants that have adapted to bright sunlight are called sun plants or heliophytes while those growing in partial shade or low intensity light are called shade plants or sciophytes. In forests, plants show stratification or layering as they are arranged in different strata due to their shade tolerance. Heliophytes (sun plants) have higher temperature optima for photosynthesis and also have high rates of respiration. On the contrary, sciophytes (shade plants) possess low photosynthetic, respiratory and metabolic activities. Ferns and several herbaceous plants are shade tolerant - plants. They grow on the ground under the dense canopy of trees.
• Plants Adaptations to Water Scarcity and Heat:
• Many species of plants are adapted to dry habitats and high temperature conditions e.g. plants of hot deserts. They are termed as Xerophytes. The xerophytes have special adaptations to withstand prolonged period of drought. These are of four types - ephemerals (drought escapers), annuals (drought evaders), succulents (drought resistants) and non-succulent perennials (drought endurers).

(i)   Ephemerals (drought escapers): The xerophytes which evade dry conditions by remaining in the form of seeds but live for a brief period and complete their life cycle during the rains. Common examples are Euphorbia andArgimone etc.

(ii) Annuals (drought evaders): These are the xerophytes which continue to live for a few months even after rains in hot dry conditions. They have modifications to reduce transpiration. Common example is Echinops.

(iii)       Succulents (drought resistants): These xerophytes have fleshy organs to store large amounts of water. Succulence results from the proliferation of parenchyma cells, enlargement of vacuoles in cells as well as due to reduction of intercellular spaces. Plants like Opuntia, Euphorbia, and Asparagus etc are noted for having fleshy stems which are green and photosynthetic. In order to minimize the loss of water, such xerophytes have not only gone through a wonderful morphological adaptation of reducing their leaves to leaf spines. At the same time, such xerophytes or Succulents do possess a very thick cuticle, sunken stomata which open during night only for the purposes of conserving maximum water--- (Question asked in CSP/ GS-2013).

(iv) Non-succulent perennials: These are true xerophytes. These perennial plants have many morphological modifications to withstand dry conditions. These have extensive root system that spreads along the soil surface to absorb maximum amount of water. They also possess waxy coatings on leaves, sunken stomata, reduced leaf blades etc. to reduce transpiration. Examples include Acacia, Zizypus jujube and Calotropis etc.

      Noted further that there are many tropical plants e.g. grasses which grow in hot and dry climates. These therefore come to possess a very unique and efficient photosynthetic pathway called as C4 pathway of photosynthesis. As a result of this, such plants are not only able to survive in conditions of water scarcity, but are also capable of achieving very high rates of photosynthesis in the midst of this water scarcity and that too under abnormally high temperatures.

       Many xerophytes even accumulate an amino acid proline in the cells of leaves to maintain osmotic and water potential. On the other hand, Chaperonins (heat shock proteins) are also present in some xerophytes which provide them physiological adaptations against high temperatures. Heat shock proteins help other proteins to maintain their structure and avoid denaturisation at high temperatures.

• Plant Adaptations to Aquatic Environments:
• Plants which grow in water or water rich sub-stratum are called hydrophytes. By adapting themselves to such aquatic habitats, these hydrophytes come to possess some of the following adaptive features such as:

 (i) Mucilage: Submerged parts of hydrophytes are covered with mucilage for protection.

(ii) Absent or poorly developed Roots: These may be absent (e.g. Wolffia) or poorly developed (e.g. Hydrilla). If present, they may serve the function of anchorage (e.g. Ranunculus). Instead of root caps, root pockets are present (e.g. Eichhomia, Pistia).

(iii)       Stems: Stems are generally weak, slender and have long internodes (e.g. Hydrilla).

(iv)       Leaves: In surface floating hydrophytes, leaves are generally large, broad and thick (e.g. Victoria). In submerged hydrophytes, leaves are either ribbon-shaped (e.g. Vallisneria) or finely dissected (e.g. Ceratophylium). Heterophylly (occurrence of more than one type of leaves) is common in partially submerged hydrophytes (e.g. Ranunculus).

(v) Inflated organs: Special air-storing organs occur in floating plants e.g. petioles or leaves for storing air. Moreover, presence of aerenchyrna (large air spaces) helps to transport oxygen produced during photosynthesis to other parts including roots. These organs also impart buoyancy to the plants.

• Plant Adaptations to Saline Environments:
• The plants which grow in saline environments are called halophytes. Saline environments have high concentrations of salts (e.g. NaCI, MgC12, MgSO4 etc.) in soil or water. Halophytes are found in tidal marshes and coastal dunes, mangroves and saline soils. They have the ability not only to tolerate high concentrations of salts in their rooting habitat but are able also to obtain water from the same. Halophytes inhabiting hot and dry conditions possess characteristics of xerophytes like succulence in leaves, stems or both for storing water in large sized cells. It helps in diluting ion concentration of salts.

Connecting concept: How do mangroves survive under extremely salty habitats?

Mangroove plants are found wonderfully adapted to marshy conditions of tropical deltas and along ocean edges for example, in India in Sunderban delta. For survival under extremely saltish conditions, these plants notably have adaptations to excrete salts through salt glands present on their leaves while some excrete salts from their roots as well. Many species of mangrooves have high levels of organic solutes (e.g. proline and sorbitol) for osmoregulation. Green algae Dunaliella of hyper saline lakes tolerate saline conditions by accumulating glycerol in the cells for osmoregulation. In Mangroove forests, Avicennia and Rhizophora are the dominants. In marshy areas, many halophytes have prop roots and stilt roots to pro-vide support ; “pneumatophores” (negatively geotropic vertical roots) having lenticels for gaseous exchange by taking up oxygen from atmosphere and transporting it to the main roots. Such adaptations help them to cope with saline and anaerobic conditions in wetlands. Still others develop vivipary (seed germination while being attached to plants) to escape the effect of salinity on seed germination.

Plant Adaptations to Oligotrophic Soils

• Oligotrophic soils refer to those soils which have very low quantity of nutrients or nutrient content. Such type of soils generally develops in old and geologically stable regions e.g. tropical rain forest regions. Nutrient retention capacity of such soils is poor due to intense weathering and high rates of leaching. Therefore, the plants that survive under such soil conditions are known to possess mycorrhizae (mutualistic association of plant roots with fungi). Mycorrhizae help in absorption of water, minerals (especially retrieval of critical elements like phosphorus from organic compounds) and protection from pathogenic organisms. This natural association has formed the basis of modern day’s agricultural practice called as mycorrhizal biotechnology under which plants have not only been enabled to grow in nutrient deficient soils, but have also been vested with an ability to resist drought and soil borne pathogenic conditions- (Question asked in CSP/GS-2013).

STRATEGIC ADAPTATIONS IN ANIMALS

Other than the most familiar adaptations so called as behavioral adaptations exhibited by the animals say in the form of migration, suspension, hibernation or aestivation as noted above, some of the animals do exhibit a unique kind of adaptation of blending with their surrounding environment so as to avoid themselves from being eaten by their predators, a phenomenon referred to as camouflage. While some animals do exhibit a kind of behavioral or morphological adaptation to attract their mate say for example, bright plumage in birds.

Camouflage (cryptic appearance)

It is the ability of the animals to blend with the surroundings or background. In this way, animals remain unnoticed for protection or aggression.

Examples

(i)   A stick insect resembles the twigs. It has slender, dull coloured body and moves very slow. This way, it conceals in the small twigs of plants in order to protect from predators.

(ii) White crab which mimics perfectly with the background i.e. white pebbles and it is difficult to distinguish the crab.

(iii)       Leaf insect is green in colour, has flattened body with yellowish irregular spots on it.  It resembles with that of a green leaf thereby camouflaging to avoid predators.

(iv)       Certain butterflies are brightly coloured from above and have dull colours on the lower surface. These butterflies settle on dead or dried leaves by folding their wings and this way deceive their predators.

Mimicry

It is generally considered a defensive mechanism adopted by palatable organisms to protect themselves from predators. It also includes deceiving or alluring of the prey at the hands of

Stick insect (A) leaf insect (B).

predators. It can be defined as the superficial but close resemblance of one organism to another or to the natural objects among which it lives that secures its concealment, protection or some other advantage. In order to deceive the predator or prey, the subject conceals itself in its surroundings (background).

In such situations, the subject is known as mimic or mimetic and the object it copies is called the model. Mimetic animals, in addition to colour, also imitate their models in shape, size, action, attitude etc. Mimicry is of four types:

(i)   Batesian mimicry: The phenomenon of resemblance of palatable prey species (mimetic) to unpalatable ones (model) in order to deceive the predator is known as Batesian mimicry. For example, Viceroy Butterfly mimics the unpalatable Monarch butterfly to protect itself from predation as the predator usually does not prey upon the Monarch butterfly.

(ii)  Mullerian mimicry: In nature, a set of two or more unpalatable related species attempt to resemble each other thus compounding their dispelling effect in the mind of their common predators. This phenomenon is called Mullerian mimicry e.g. Monarch butterfly and Queen Butterfly.

(iii)       Aggressive Mimicry:  Sometimes, predators take advantage of mimicry phenomenon. Here, predators really become the proverbial wolf in sheep's clothing. This is often called aggressive mimicry.

• For example, Praying mantis use different strategies to blend themselves with the immediate surroundings to deceive the prey on which these feed. The preying mantis may be green in colour, thus mimicking the colour of vegetation in the background or may resemble a dead curled-up leaf or its thin body can easily be

Viceroy butterfly (left) which mimics the monarch butterfly (right).

• confused with a twig (concealing type of aggressive mimicry). Spiders have generally enlarged abdomens whose appearance is similar to flower parts. Spiders imitate the flowers of orchids that frequently drop into their web and this way allure insects which fall prey in their webs (alluring type of aggressive mimicry).

(iv)       Feigning Death or Conscious Mimicry: Certain organisms, sensing danger from predators, pose as if they are dead objects. Tenebrinoid beetles are famous for attaining motionless pebble-like appearance when they are in danger from predators. This phenomenon is called feigning death or conscious mimicry.

Warning Colouration

Sometimes, concealing form as well as coloration enables the animal species to avoid its natural predator. For example, brightly coloured and highly poisonous dart frog (Phyllobates bicolor and Dendrobates pumilio) inhabiting tropical rain forests of South America are easily recognized and avoided by their predators.

Adaptation to Water Scarcity in Animals:

Animals that live in arid regions show two kinds of adaptations such as:

(i)         Reducing loss of water from their bodies, and

(ii)        Ability to tolerate arid conditions.

For example, Kangaroo rat seldom drinks water; 90% of its water needs are met from metabolic water i.e. water produced by respiratory breakdown and remaining 10% is fulfilled from food. It is nocturnal in habit and rarely comes out of its cool burrow during the daytime. It has a thick body covering to minimize water loss due to evaporation. The kangaroo rat excretes nearly solid urine and faeces. Another example is that of camel, commonly called the 'ship of desert'. Camels have unique adjustments to desert conditions; being very economical in water consumption, tolerant to fluctuations of temperature, maintenance of blood stream moisture with body cells capable of tolerating extreme heat stress, producing dry faeces and concentrated urine. During periods of non-availability of water, the animal does not excrete urine but stores urea. These animals also - Use metabolic water obtained during oxidation of fats stored in the hump.

Adaptations to cold in Animals:  Animals like barnacles and molluscs of intertidal zones of cold areas live in sea and cannot undergo hibernation. Also, sessile animals cannot migrate. These animals and some others (e.g. several insects, spiders) have adapted to excessive cold conditions by developing cold hardening. These animals are commonly called freeze tolerant organisms. They possess ice nucleating proteins which induce ice formation in the extra cellular spaces at very low sub zero temperatures. Antarctic fish (Trematomis), for example, can tolerate below 0°C temperature by accumulating glycerol or anti-freeze proteins that lower freezing point of their body fluids just like we use an antifreezer in our car batteries in extreme winters. In this way, it remains active even in extremely cold sea water in Antarctic region.

Echolocation

This behavioural adaptation is depicted by bats. These are flying mammals and are nocturnal. They do not use eyesight for locating food, path or place of rest. Instead, they produce high frequency sounds which work on the principle of sonar. The high frequency sounds after striking various objects produce echoes which are received by the bats to locate their path.