Vocalization in amphibian.

download in .pdf format

Whatever their musical qualities, vocalization are conspicuous feature of the behavior of most frogs and the toads. Although the function of frogs calls were not well understood until relatively recently most early naturalists realized that calls are given almost exclusively by males are associated with reproduction, and probably serve to attract mates.

Mechanism of sound production:

The basic mechanism of sound production in most anurans is relatively simple system. Air is forced from the lungs by the contraction of muscles in the trunk region and moves through the larynx into the buccal cavity. As the air passes through the larynx, vibrations of the vocal cords and the associated cartilage produce sound. An action of the larynx muscles shapes the sound in variety of forms.

The sound producing system involves three major functional units:

1.       The trunk muscles that powers the system.

2.       The larynx apparatus that produces the sound.

3.       The buccal cavity and the vocal sac that transmit the sound.

Bogert (1960) classified anuran calls into six categories based on the context in which they occur:

1.      Mating calls.

2.      Territorial calls.

3.      Male release calls.

4.      Female release calls.

5.      Distress calls.

6.      Warning calls.

1.       Advertisement calls: bogert used the term mating calls to describe the principal signals given by the males during the breeding seasons. These calls are now called as advertisement calls (wells 1977) because they often serve for more than one function or convey more than one message

2.       Male courtship calls: male frogs often alter vocal behavior when females are nearby , producing calls that render the male more conspicuous in a chorus

3.       Female courtship calls: some female frogs give call in response to the call of male and these are often called as reciprocation calls (littlejohn 1977) they tend to be given at very low intensity and therefore are hard to hear.

4.       Aggressive calls: many male frogs defend their calling sites and have distinctive aggressive vocalization.

5.       Release calls: male anurans usually give release calls when clasped by other males, either when the male being clasped is alone or in complexus with a female. The females that have completed oviposition also give similar calls. Usually these calls consist of a series of rapidly repeated broad spectrum notes.

6.       Distress calls, alarm calls, and defending calls: bogert used the tem distress calls to describe vocalization given by the frogs being attacked by predators. Usually these are loud screams, often with the mouth open.

Energy cost of vocalization by frogs:

Ted taigen and kent wells experimented on hyla versicolor. The rates at which individual frogs consumed oxygen is directly proportional to their rates of vocalization

At low calling rates, about 150 calls per hour, oxygen consumed was barely above resting stage. However at the highest calling rates, about 1500 calls per hour the frogs were consuming oxygen at a rate even higher than they consumed during their highest locomotors activity.

Costs and benefits of vocalization:

The vocalization of male frog is costly in two senses. The actual energy that goes into calls production can be very high and the variation in calling pattern that accompany several interactions among male frogs in a breeding chorus can increase the cost per calls.

                Another cost for the vocalization for a male frog is the risk of predation.

                A critical function of the vocal calls is the permit the female frog to locate the male frog.

Rabies

Rabies

·         Rabies viruse is a neurotropic viruse, responsible for the fatal disease RABIES among humans and several other animals

·         Its transmission occurs through the saliva of the infected animals. The virus is classified as follows

Ø  Group-ss RNA (-ve)

Ø  Order-monomegavirale

Ø  Family-rhabdoviridae

Ø  Genus-lyssaviruse

Ø  Species-rabies

·         Structure of rabies viruse: the viruse is bullet shaped with a length of about 180 nm and cs diameter of 75 nm.

·         One end of the viruse is conically rounded and other end is planar.

·         The genome is surrounded by a  lipoprotein envelope which poses spike like glycoprotein gene

·         The spike do not cover the planar end of the virion.

·         Beneath the envelope is the matrix protein layer wahich may invaginated at the planar end

·         The core consist hellcally arranged ribonucleoprotein

·         The genome is unsemented, linear single stranded RNA with –ve sense .

·         The RNA genome encodes 5 genes: the order of these genes 3’NMPGL-E is highly conserved.

·         The genes code for five different protein:

1.       N- nucleoprotein

2.       P-phospho protein

3.       M-matrix protein

4.       G-glycoprotein

5.       L-viral RNA polymerase

·         All the transcripltion or the replication events occur inside the cytoplasm in the specialized viruse factory known as NEGRI BODY.

·         The negri body are 2 to 4 nanometer in diameter and are typical for rabies infection.

·         Negri bodies are used as a definite histological proof for the viral infection.

·         Infection: infevtion of human beings are through bite of an infected animal, such as the incected dog, cat, bat, etc….

·         From the wound the viruse tracels quickly long the neural pathways to the CNS.

·         The exact molecular mechanism of this transportation is still unknown, although the binding of p protein from rabies viruse to the dyenin light chain protein have been shown in several cases of pathogenesis.

·         The protein also acts as an interferon antagonist.

·         In this way the p protein also decreases the immune system response of the host cell.

·         From the CNS the virus travels to the other organs.

·         The salivary glands and the tissues of the mouth receives high concenteation of the virus.

·         Thus allosing its further transmission ans secondary infection.

·         Life cycle:

·         After the receptor binding, the rabies viruse wnters into the host cell therough endosomal transport pathway inside the wndosome.

·         The low ph value induces the membrane fusion .

·         Thus enabling the viral genome to reach the cytosol.

·         Both receptor binding and membrane fusion os catalysed by the glycoprotein gene which plays a critical role in the pathiogenesis.

·         Any mutant viruse without gene protein cannot propagate.

·         Now the viral genome is transmited by P-L polymerase.

·         The p protein is essential co factor for the 2_polymerase.

·         The enzyme is responsible for formation of new viral protein molecules.

·         This viral polymarasse can only recognize ribonucleoprotein and canot use free RNA as template.

·         Later on the activity of polymerase switches to replication in oreder to produce the full length +ve strand RNA copies i.e. co,plementory RNA

·         These complementary RNAs are used to make new –ve strand genomes and are used as template.

·         Thay are packsged togehetr with protein which proceeed to form virus.

·         Rabies is essentially ans  overwhwlming encephalomyletis. In humans the incubation period from the time of infection varies from 6 days to a year, but is basically sbout 3-8 weels.

·         The development of symptoms and the length of the incubation period depens upon the severiety snd the site of bite.

·         It has been seen that only about 5-15% of human bitten byb rabid animals show rabies symnptoms.

·         Symptoms in humans include severe headache and high fever with alternating stages of excitement and depressions.

·         Patient have difficulty in swallowing and slight muscular stimuli in throat and chest.

·         Death usually  follows paralysis.

·         The moratality rate in rabies is about 100 percent.

·         If a person is biteen by rabid animal the long period of the incubation allows time for measures to be taken to prevent the viruse from reaching the CNS.

·         These measures include a combination of passive immunization and active immunization.

·         The active immunization includes the administration of rabies vaccins to stimulat the longer lasting production of the antibodies by t he patient.

·         Laboratory confirmation of rabies of the animal which has botten the patient is done by one of the following gmethods:

1.       Detection of rabies virus antigen in clinical specimen by the use of the fluorescent antibodies.

2.       Isolation of virus from the urine, saliva, spinal fluid of tissues by ennoculation into the brain of mice.

3.       Demonstration of the inclusion bodies i.e. the negri bodies in the nerve cels of the brain

·         In all the above cases the negative results do not exclude rabies and for theis reason the animal should not be killed but kept under observation for atleasr two weeks.

If the animal shows the symptoms of rabies, the human victim must be vaccinated.

Nest building in birds

The nest building in the birds is an innate behavior. Depending upon the condition of the young after the hatching from the egg the birds are classified into two types.

1.     Precocial: the young of these birds are quite conscious and are able to leave their nests and survive out of the nest. Ex. Hen

2.    Altricial: the young of these birds are very weak and they cannot survive out of the nest. Their skin is naked and the eyes are closed.the nests of these birdsa re generally build very high above the ground.

Nest building is a unique and beautiful character in the the birds.the nest building is the safest way to provide the protection to the eggsand the developing ypung ones. For safety the nests are build inaccessible, well armoured, camouflaged and in some cases they are build in colonies.

The nest building has a very close relationship with the copulation. The oesstrogen can induce the nest bilding in the birds. Primarily the nest building has benn suggested to arrive in the birds due to sex fidgeting, which is veery common before and after the mating. The nest is first the sex site.

The male and females of birds may equlally or unequally take part in the nest bilding. Von tyen and Berger classified the birds in 6 categories depending upon the part played by either of the sexes of the birds. According to them the birds are of following 6 types.

1.     Both males and the females equally contribute to build the nest. Ex. Wood pecker

2.    The materials are brought by the females and the males build the nest. Ex frigate birds

3.    The building materials are brought by the males and the females build the nest.ex pigeion

4.   The entire nest building is dome by the femae alone unaided by the male. Ex, humming birds

5.    The entire nest building is done by the male unaided by the females. Ex beaver birds

6.   The materials are brought by both the sexes but the nest building is done by the females. Ex. Crow

The way of nest buildimg varies greatly according to thte type of the materials used.

Nest building is instinctive character in birds, which is guided by the brain and may improve with experience. The young birds are found to buiod coarse nests as compared to the mature ones.the methods of building nests varies greatly. The most elabi\orate method is the tying of the grass to the branches of the trees.

Site of nest building:

The site for nest building selected to be very familiar. For ex.

1.     The eagles living on high altitudes build their nests at bery high altitudes among the open cliff faces

2.    Arboreal birds build their nests among the branches and leaves of the trees. Ex beaver bird

3.    The ground birds build their nests on the ground. Ex hen

4.   Water birds build their nests around water, ex heron

There are many birds which build their nests in a surrounding different from their original habitat. For ex the bee eater is not a ground bird but horizontall tunnels in the earth banks.    Some ducks are found to build their nests on the ground.

Types of nests:

The types of nests vary greatly from species to species and show a great diversity.

a.   Some ground bords may just scrap a little of the earth and lay their eggs in the depression and cover them with the soil or the vegetation.

b.   Some ground birds build their early nests on the ground and the later ones on the small bushes.

c.    Some birds nest in old holes and crevices which they line with soft materials.

d.   Some birds build tunnels in the earth banks.

e.    Som birds may build cup of grasses on the fork of the branches.

f.    Most woodpeckers excavate a nest cavity in dead or living trees. They first bild a horizontal entrance with small edges few cm in length. After thet the vuild vertically downwardsand carefully remove all the shsvings. The woodpecker use the same tunnel to rear the next brood ommediately.

g.   The tailor birds sew the hanging leaves of the branches together woth the fibers to form a cup like structure.

h.   The weaver birds or the bayas make a basket like nest with lling thin entrance tube. The egg chamber is the wodest part. In bayas when the incomplete nest is like an upside down cup the female baya chose their mates, the male then completes the basket downwards. The bayas use their nests for only one generation and they build a new nest everytime the nedd to lay eggs.

i.     The old nest of the bayas may be used by the other species of the birds like sparrow and white throated munnia.

j.     The hornbills chose a deep hollow in the tree tthen the hen bird descend in the hollow. She builds up the wall from inside till the mouth to leave a small hole from where she can have the food brought by the males, the building materials consists of her own droplings

k.   The abandoned nests of the wood peckers are used by many other species of the birds like blue birds.

l.     The king penguins holds the single egg on the top of its feet and incublate likewise.

m. Special or colonial nestings:

i.             About 13% of all the birds in the world and 93% of all the marine birds nest in the colonies.

ii.           The habit may have developed probably fo the safety or due to limited nesting sites provided by islands and the cliffs.

iii.         According to Von tyne and Berger these social nesting may involve:

1.     Members of the same species

The nests of these types may be of two types:

I.             Communal nesting: here one to four couples of the birds build a common nest in which all the females lay the eggs. Incubation of the eggs and the feeding of the young ones is done by all the adults. Ex hen

II.           Cooperative nests: in this flocks of hundred or more pairs of birdsbuuild the nest and each pair has their own nestsing chambers.

2.    Two or more species mixed together.

Mixed colonies my be of different types:

I.             Large numbers of two or more species nest together in an area. Ex. Terns, herons, frigates.

II.           One or more pairs of species living in the midst of large colony of other species.ex. skuas with penguins.

III.         A number of small birds in close associatin with large birds. Ex,. Hose sparrow building their nests inside the osprey’s nests.

IV.         Different genera of birds building their nests in close proximity. Ex myna, king crow.

Nest parasitism:

A)  Obligate parasites: no nests are build by such species. They neither incubate their egg nor they care for their young ones. They lay their eggs in the nests of the other species called fosters or the hosts. Obligate parasitism is found in 5 different families.

1)    Cuculidae:  cuckoo family

2)   Indicatoridae: honey guiders

3)   Analidae: block headed duck of SA

4)  Ploceidae: weaver bird family

5)   Icteridae: troupial family.

B)  Non obligate parasites: they are those species which incubate their eggs or care for their young ones but either frequently of rarely. They lay one or more eggs in the nest of other birds.

The parasites are of two types:

i)            Nest parasites: they are those birds which unsurp the nests of other species and lay their eggs and incubate their eggs their only. Ex. Yellow tailed hornbill

ii)          Egg parasite: they some times lay their eggs in the nest of the other species. Ex crow

Conclusion: the survival of any species of the animal depends upon itw reproductive success.

          For the success the birds exihibit a high degree of care to their young ones. The chief form i

foot and mouth disease

the causative virus of the foot and mouth disease id similar to that of the rheoviruse. it is an acute communicable disease of hoofed animals like various cattle- sheeps, goat, swine etc. humans are susceptible for infections and they may transmit it to other healthy individuals. animals who recover from the disease may act as asymptomatic carriers of the virus.
   Infections generally occur through the abrasions of the skin ans mucous membranes. in humans the disease is generally mild and is characterised by symptoms as follows:
1. high fever
2. salivation
3. vesicular eruptions in the mucus membrane of oesophagus, skin of palm sole and the finger and toes.

vesicles occur on the mucosa of the mouth between claws of feet and other parts of the body. the mortality rate on the animals is low but the disease causes a great economic loss due to reduced meat and milk production. recovery from the disease confirms immunity to particular viral serotypes involved in the infection. vaccines are available and are made from inactive virus grown in tissue culture.
   However outbreaks are frequently linked to incompletely inactivated inactivated vaccines or escapes of live and active viruses from research and production facilities. laboratory diagnosis of FMD is done by compliment fixation virus neutralisation test.  at present the vaccine developed by the DNA recombinant technology are used against the virus.  in this method a Gene from FMD viral coat protein is spliced in E.Coli and the bacteria containing the plasmid then produce the viral protein antigen. this antigen is extracted from the bacteria and used as completely safe immunising agent.

shelford's law of tolerance

download in .pdf format


Liebig proposed that too little of something can be alimiting factor. but too much of certain substance may also act as a limiting factor. thus organism have an ecological minimum and maximum limit of tolerance the range in between is called the limits of tolerance.

the concept of limiting effect of maximum as well as minimum constituents is included in shelford law of tolerance(Shelford 1913). 


All physical requirements may be well within the limits of tolerance for an organism, but the organism may fail due to biological  interrelations such as competitions and the predations.............


some subsidiary principles to law of tolerance may be ststed as follows:
1. organisms may have a wide range of tolerance for one factor and a narrow rangw for the other.
2. organisms with side range of tolerance for limiting factors are likely to be most widely distributed.
3. in some cases whwn conditions are not optimal for a spedies with respect to one ecological factor then the kimits of tolerance may be reduced for other ecological factors.
4. sometimes it may happen that an organism may not be living at the optimum range of a particular factor. in such cases the othes physical factors are founf to have great importance.
 ex: the cord grasses which dominates the east coast salt  marsh areas, actually grows better in fresh water than in salt water. but in the nature it is found in only salt water, apparently because it can extrude salt from leaves better than any of its competitors.
5.  the limits of tolerance for reproductive individuals, seeds, eggs , embryo etc are usually nonreproducing individuals.... ex: an adult cypress tree will grow continually submerged in water or dry upland, but it cannot reproduce untill there is moist unfloded ground.

download in .pdf format

significance of the food chain

it helps us understand the feeding relationships and the interactions between organisms in any ecosystem.

it also help us to comprehend the energy flow mechanism and the matter flow in the ecosystem and teh pronlem of biological magnification.

methods of studying the food chain:
 many direct and indirect methods are used to study the food chain relationships in the nature. we will discuss about some of them here.
1. gut content analysis:
     it is considrerd the most convenient methods of analysys of the food chain. the               elementary cannal is opened and undigested food materials are read for. in this way the gross reading is made of what fodd habit is followed by the animal and the codd chain relationship is drawn. this is simple and convenient method.


2. use of radioactive isotopes:
    radioactive isotopes such as phosphorus32 are used in food items and then are followed and detected along the food chain by a GM counter is a good method to analyse and read the food chain relationships. this method is accuarate but there is possibility of contamination of environment by these rsdioactive isotopes.

3. precipitaioon test:
   DEMPSTER(1960) used this test to study the pedators of the broom beetle (phytodecta olivacea)

to be contd............

law of minimum(given by von liebig)

law of minimum:
the law of minimum was developed by von liebig in the 19th century.
an organism(micro organism, plant or animal) is simultaneously subjected to the influence of various factors( such as humidity, temperature, atmospheric pressure, oxygen concentration etc.....). but some of these factors affects the organism more than any other factors.
   von liebig developed  the concept of law of minimum by evaluating the role of these factors.
    the law of minimum states that "an organism requires a minimum quantity of a particular nutrient for proper growth"

for example: a plant will not grow well if the soil is deficient in on of the essential nutritive component of the soil, even if all the other components of soil are present in a healthy concentration.   but if the plant is provided the deficient nutrition to the plant in healthy concentrations, the other components of the soil becomes active and the plant is now able to utilise those nutrients and grows well.

liebig is commonly known as father of fertiliser science