Biodiversity

Monday, May 15, 2006

ECHOLOCATION IN BATS AND WHALES

Echolocation is the biological sound used by mammals such as bats, dolphins and whales to produce sound waves that encounter objects and these sound waves create a complex sound that returns back to their ears. Echolocation is some times known as Biosonar. Bats that echolocate are of the suborder Microchiroptera from the mammals order Chiroptera. The bats of Microchiptera suborder produce all manner of sound for echolocation and they do it for the purpose of catching prey such as insects.


The scientsts said that "not all bats echolocate, but bats of the sub-order Microchiroptera do echolocate" (4). Furthermore, members of this sub-order produce all manner of the sounds through echolocation. The sub-order of this group also does echolocate in order catch many preys and other many insects. On the other side" bats of moustached are said to be highly dedicated to the task of echolocation and are also said to be an excellent species" (4).


The ear of the human is thought to be unable to hear the echolocation abilities of the bats. Bats are also said to produce different types of sounds during the echolocation process for example, "mustached bat is thought to produce a biosonar sound consisting of a frequency which is stable” (1,3,4). Bats catch their prey by flying around, they do so by using their sonar signals as information about the food in the area. The sonar signals which are used by bats act like the waves of the sound, because sonar signals that “the bat produce return in the form of the echo, which the bat detect with auditory structures" (4).


On the other side whales use “echolocation to sense their objects and hunt their prey” (3). In echolocation highly pitched sound is sent by the whale. The sound is sent in this way, the sound bounces off the object and some returns to the whale. Therefore, the returning echo is interpreted by determining “the shape of the objects, direction, distance and the texture" (5). Teeth of the echolocation start with a series of the low-frequency. Their “echoed sound waves are from the flat-filled cavities of the bone that are at the lower jaw” (5). These sounds are "conducted through the bone to ear and the brains where as the location of the object is interpreted" (5). The whale can determine the distance to an object, its size, shape, the speed that the object is travelling and its texture.

It is also possible that the whales may use other types of sound to perform similar functions as the traditional sonar signals of the dolphins. While on the other hand "whales do not produce high frequency, broad band, short duration clicks" (5). They also produce lower frequencies as compared to the mustached bat. The echoes returned as the low frequency sound bounce off features in the ocean. In conclusion, one can say that the echolocation process is useful in bats because it seems unique in bats. This is because echolocation is only unique to the bats.


References:

1. Ketten, D. and Madin, K. 2005. How to see what whales hear. [Online]. Available from: http://www.whoi.edu/oceanus/viewArticle.do?id=5759 [cited 24 May 2006, 14:24]

2. Kruse 1996 Echolation in the bat. [Online].Available from:
http://www.npa.uiuc.edu/courses/physl490b/models/bat_echolocation/bat_echolocation.html [2006, May 24]


3. Roth J. 2006.Echolocation [Online].Available from:
http://www.eparks.org/wildlife_protection/wildlife_facts/bats/echolocation.asp [2006, May 24]

4. Wikipedia contributors. Echolocation [Internet] Wikipedia, The Free Encyclopedia 2006 May 07, 18: 16 UTC [cited May 15, 16: 10]. Available from: http://en.wikipedia.org/wiki/Animal_echolocation

5. Wikipedia contributors. Echolocation [Internet] Wikipedia, The Free Encyclopedia 2006 May 13, 00: 49 UTC [cited May 15, 16: 10]. Available from:
http://en.wikipedia.org/wiki/Whale


Lizzy Maluleke
CSIR PTA
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THE ADAPTATION REQUIRED TO MAKE THE TRANSITION FROM AQUQTIC TO TERRESTRIAL LIFE USING AMPHIBIANS AS EXAMPLE

Amphibians belong to the phylum chordate. Amphibians are organisms which live double life, both aquatic and terrestrial. In the aquatic environment, amphibians use gills to breath as opposed to the terrestrial environment where they lungs to breath. Even though amphibians can live on terrestrial environment but they do not have the ability to adapt on land. Their inability to adapt to the terrestrial environment can be attributed to some of the limiting factors such as population growth and diseases.

In the water algae are thought to be the producers. This means that algae can be able to produce their own food. Therefore animals in the aquatic environment will feed on algae. These also apply to the amphibians in the water, because they feed on the algae. Algae also help the amphibians during the laying of their eggs; the eggs are laid and remain hanging around the algae until hatching. The young tadpoles hatched will feed on the algae until their development into adult frog and move out of the water into the terrestrial environment.

Another example of the amphibian which has the double life is the crocodile. Crocodile also spend much of their time in water, where they find it easier to catch their preys such as goats and antelopes when they coming to drink water. In a sunny day they move out of the water to bask for the sun, but when their enemy comes the crocodiles run back into the water for hiding. They are able to live on both environments, aquatic and terrestrial because as like in frogs they possess both the gills and the lungs.

In almost all amphibians, an adaptation in the terrestrial environment is not easy. Their failure to adapt to the terrestrial environment can be attributed to many limiting factors such as population growth, climate change, urbanization and the drying out of the coal swamps. As the population continues to grow, this means that more land is occupied by the people and the buildings. The more the population grows, the higher would be the demand for the fossil fuels such as coal, oil and gases. The more the fossil fuels are burnt, the higher would be the temperature. The high temperature will affect the life of the amphibians in the terrestrial environment, because of the high rate of evaporation which will occur.

The adaptations in the terrestrial environment by the amphibians will continue to deteriorate as long as human beings continue to pollute the environment through their anthropogenic factors. As amphibians are surpassed by the reptiles in the terrestrial environment, in the aquatic environment such as the rivers amphibians were multiplying in numbers in the late Permian. Even today the most suitable environment for the amphibians is aquatic environment.

In concluding paragraph, it can be easily said that amphibians have not fully adapt to the terrestrial environment. Their failure to adapt to the terrestrial environment can be attributed to the many limiting factors such as climate and the drying out of the swamps. Lastly, the aquatic environment favours amphibians.

References

Wikipedia contributors. Amphibian [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 09, 00:20 UTC [cited 2006 May 09]. Available from: http://en.wikipedia.org/wiki/Amphibian

Wikipedia contributors. Chordata [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 08, 12: 15 UTC [cited 2006 May 09]. Available from: http://en.wikipedia.org/wiki/Chordata

Masiya Kedibone
CSIR Pretoria
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Cell No: 073 2519071
Tel No: 012 8412123
Fax: 012 842 3676
E-mail:kmasiya@csir.co.za
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REASON WHY PLACENTAL MAMMALS HAVE COLONIZED LAND, WATER AND AIR

Placental mammals are considered the largest group of mammal species. They are class of vertebrates animals, which is characterised by mammary glands. In females it produces milk to nourish their offspring .most of the placental mammal are warm blooded animal and they also have fur (hair) which they use to protect their skin agaist cold. fur helps to insulate,while the warm-blooded part helps to regulate body tempareture . Having fur and warm- blooded bodies enables them to adapt various environment. placental mammal includes species such as elephant, whales, bats and farm as well as work animals. Also human are regarded as placental mammal.[1]

Placental animal have colonise all the environment land, water, and air. Because of their bodies that can regulate the tempareture and also the modification that they underwent during environmental change which influence other species to adapt different environmental condition. some mammals adapt terrestrial environment as the cannot cope climate in the sea, while other adapt aquatic environment because they cannot move on land. They also adapt different enviroment because of the abundant feed that this different environment provide.

For example;whales was suggested living at the edge of the water in terrestrial,they get into water when they find that water is rich source of food. And inside the water there is no competition of foods .they tend to adapt aquatic style and this results in the modification of their bodies. Because they where living in the new environment and eating different food some change the structure of teeth so that they can eat their prey easily.[2]

This can indicate that during evolution and adaptation of placental mammals to colonise different environment, they underwent modification on their bodies. Some modification cause problems when they move to land, “they have to develop water proof external layers, internal gas exchange systems and ways of reproducing that did not evolve water “.[3] Some develops strong support systems endoskeletons and exoskeleton that will enable them to move on land. But not all placental mammals have managed to solve the problem of moving to land, they then adapt to their origin habitant which is the aquatic environment. [3]

It was suggested by paleothropologist that evolution of most species including placental mammals evolve from aquatic environment, it can be suggested that those mammals that are still occupying aquatic environment is because they fail to meet the modification that allows them to walk on land or on air. It was a benefit for placental mammal to have lighter bodies and strong legs that can suport them against gravitational force that found on land. and also to have bodies that can retain water, so some develop waxy and water proof cuticle which is useful to conserve water in the body.[3]

The adaptation of different mode of locomotion also help the placental mammal to colonise most environment. those mammal that adapt quadrapedal find it easy to live on land ,and those that develops wing like birds(bat) they colonise air simple,while those that fail they retain their fins and develop support that can allow them to move around outside water but mostly find themselves in the water as they can not adapt for a period on land.[1]

Some Placental mammals colonize land and water forduring reproduction period as they cannot produce in the aquatic environment , mammals such as sea lions they give birth outside water.so this indicate that having body that can regulate body tempareture it became easy for the species to colonize many environment, if the climate is not favouring them they can regulate it to favour them inside their body.[2]

In nutshell placental mammals have a better chance to colonize vast environment because they are warm-blooded animals that can regulate their body temperature and they have underwent modification on mode of locomotion that helps them to adapt many habitants.when they adapt to diferent environment the end up choosing diet which tend to enhance their metabolic rate which increase the regulation of tempareture. When they move out of water they develop body structure which is endoskeleton which support endothermic the process that control body tempareture.thats why it is simple for placental mammal to adapt variety of environment.

Reference:

1. Hastings.L. Mammal Adaptation.[Internet] [cited 2006-May-11]Available from: http://animals.about.com/cs/mammals/a/mam101ab.htm

2. David Burnie ,B.S.Mammal, [internet] Microsoft® Encarta® Online Encyclopedia 2006 [cited 2006 may 8]. Available from:http://encarta.msn.com/encyclopedia_761561349/Mammal.html

3. Evolution for Teaching. Plant and Animal Evolution; [Internet] University of Waikato. [Cited 2006 May 08]Available from: http://sci.waikato.ac.nz/evolution/AnimalEvolution.shtml

Mr Elelwani Muanalo
NISL- Ecological Informatics Student
CSIR Pretoria
Tel: +27 12 841 2133
Fax: +27 12 842 7024.
Email: emuanalo@csir.co.za
My bloger URL: http://muanalo.blogspot.com/

DESCRIPTIONS OF ALL MEMBERS OF HOMINIDAE

Hominidae are great apes that include human, chimpanzee, gorillas, gibbons and orangutans. DNA showed the relationship between human orangutans, chimpanzees, gorillas and gibbon. Some Hominidae characteristics include complex social behaviour, sexual dimorphism and mostly are terrestrials.

Humans are bipedal primates belonging to the mammalian. Humans have a highly developed brain capable of abstract reasoning, language and introspection. Human are social by nature. Human are mainly adapt to utilizing system of communication such as language for self expression and exchange ideas. Social structure of human consists of cooperating and competing groups. Human are also inborn appreciation for enjoyment, beauty and aesthetic which combined with a human desire for self expression, has led to cultural innovations such as art, literature and music. “The distance between human and gorilla is 2.27%, the distances between human and Orangutans is 3.6%; the distance between human and gibbons is 4.76% and that the distance between the chimp and gorillas is 2.25%” (1).

Gorillas are knuckle walkers. The height of adult males ranges between 1.65m to 1.75m and their weight from 140 kilogram to 165kg. The majority of gorillas are covered with brown hair on their bodies. They have a large head with a bulging forehead, tiny ears, and small dark to brown eyes. They insist extreme sexual dimorphism, males being more twice than size of females. Gorilla social system is usually composed of single adult male with many females. . The relationship between female to female is very poor, their only link is that they like the same guy. Gorillas live in open canopy place in order for them to access vegetation. Gorilla eats vegetation such as leaves, fruits, shoots and stems. “Two species of gorilla share 97.7% with human and two species of orangutans 96.4 %”( 2).

Chimps found a little in western Africa and across the Equatorial belt in mid-Africa Chimpanzees (chimps) are knuckle-walkers and are terrestrial. The majority of primates walk on the flat on their hands, but chimps walk on their knuckles with their hand turned over. The forearms are longer than the hind limbs, and the bonobo has a short thumb. The average height of male chimpanzee varies from 0.66-1m with the weight from 26-50kg. The height of a female varies from 0.9-1.2m and the weight 35-70kg. They are covered with black hair on most of their body.). Chimps are mostly eating fruit but they also eat termites, ants, flowers, seeds, shoots, leaves, and bark and shrub level forest. Male tends to hunt. They will eat monkeys, antelopes, pig and anything catches able. They are usually hunted in groups. Most of the grooming bouts and instances of food sharing occur between males and females. In chimps females to female relationships is strong. People and Chimps have similar DNA (about 98% of human and chimpanzee DNA is identical) (3).

The majority of Orangutans are arboreal; this is clearly indicated by anatomically in the structure of their hips and shoulders. It is more like the climb around with hand Orangutans are too heavy to fling themselves. Sometimes they get down and walk from one tree to another. Orangutans also show size of dimorphism. Adult males are approximately 1.4m tall and up 82kg in weight. They are spending nearly most of all of their time on the trees, making a nest in the trees every night. Orangutans are really endangered. They are found in Sumutra and little on Borneo. Orangutans are also fruit eaters and they move slowly. However, they can able cover many territories in a year. Orangutans have little social organization. Sometimes female will copulate with immature males who do not have secondary sex characteristics. Sometimes young males rape females which are unusually in primates other than human (4).

Gibbons are small, slender, long armed and tree dwelling apes. They are arboreal. They are usually spending more of their time in trees. Gibbons have a small, round head, very long arm and short, slender body. They are covered by with light to dark brown colour in their bodies. They have hands which are similar like human. The height of males is approximately 90cm and weighs about 7kg. Gibbons are social animals that are active during the day. They live in small, stable family group consisting of a mated pair and their immature offspring.

The DNA of chimpanzees and human were found to be identical. Chimpanzees are closest relative of human. Orangutans are slightly less close phylogenetically. It is appear that chimps, gorilla, human, gibbons and orangutans make up the family Hominidae.

References

1. Myers, P. 2001. "Hominidae" [Internet], Animal Diversity Web. Accessed May 19, 2006. [Cited 2006 May 23, 11:11]. Available from: http://animaldiversity.ummz.umich.edu/site/accounts/information/Hominidae.html


2. Silverton J. Human’s closest relative [Internet], Animal Diversity Web. Accessed May 23, 2006. [Cited 2006 May 19, 12:17]. Available from:
http://www.nyu.edu/projects/fitch/resources/student_papers/silver.pdf


3. Wakibara J.V. 2001. [Internet], Animal Diversity Web. Accessed May 23, 2006. [Cited 2006 May 19, 12:05]. Available from:
http://mahale.web.infoseek.co.jp/PAN/8_1/contents.html

4. Wikepedia Contributors. Human, Free Encyclopedia [Internet] Accessed 2006, May 10, [Cited on 2006 May 11, 10:12] Available from: http://en.wikipedia.org/wiki/chimpanzee

5. Wikepedia Contributors.2006. Gorillas, Free Encyclopedia [Online] Accessed 2006, May 10, [Cited on 2006, May 11, 12:45] Available from: http://en.wikipedia.org/wiki/Gorillas

6. Wikepedia Contributors.2006. Human, Free Encyclopedia [Online] Accessed 2006 May 10, [Cited on 2006 May 11 13:30], Available from: http://en.wikipedia.org/wiki/Human

7. Wikepedia Contributors.2006. Orangutans, Free Encyclopedia [Internet] Accessed 2006, May 10. [Cited on 2006 May 11 14:17], Available from: http://en.wikipedia.org/wiki/Orungtans

Masiya Kedibone

CSIR PTA

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Cell No: 073 2519071

Tel No: 012 8412123

Fax: 012 842 3676

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DISCUSSION OF IDENTIFYING CHARACTERISTICS OF EACH ORDER OF PLACENTAL MAMMALS, INCLUDING A LIST OF ANIMALS REPRESENTING EACH ORDER

There are twenty Orders which are found in placental mammals. These include “Carnivora, Chiroptera, Perissodactyla, Artiodactyla, Primates, Insectivora, Proboscidea, Sirenia, Logomorpha, Macroscelidea, Dermoptera, Tubelidentata, Hyracoidean, Pilosa, Scandentia, Xenarthra, Rodentia, Pholidata, Afrosoricida and Cetacea”(4). These orders have characteristics which identifies them from each other.

Animals that are found in order Carnivora include dogs, cats, lion, skunk, walrus, and sea lion (1). “Animals of the order carnivora have sharp claws and long cone- like (5).” “Some teeth are sharp and they act like scissor blades. They have furry or hairy coat. The main feature of the head is squarish snout. Their eyes are small and ears are internal”. (4).

Chiroptera had long slender fingers covered by sheet leathery skin. The skins were connected to their sides, legs and tails to make a wing. The example for Chiroptera was bats. Bats had modified forelimbs which support wing membrane. "Bats had most elongated parts of the limb are those of hands (metacarpal bones) and fingers" (4). “Bats have five unique muscles present in the patagium and use addition muscle which is found in the chest and back to move the wings up and down. The limbs of hind are unique”(5).

Animals that belong to this order “Artiodactyls include cow, sheep, pig, giraffe and hippopotamus. This is the order of even toed hoofed animals that have only two toes on which they stands. Standing on two toes provides better control than on a flat foot. Lagomorpha is the order which have animals such as hare, pikas, cotton rabbit and jack rabbit. They have two pair upper incisors and they do not have canine teeth and molars do have roots” (1).

Order Dermoptera consists of flying lemurs or culugos. “The lower incisors are comb-like teeth with twenty prongs per tooth” (3). “Animals that belong to order Xenarthra include sloths, armadillos and anteaters. These animals have backbone that provide extra strength and support when they are burrowing. They have a unique glup todont.” (1).

Hyracoidea is the order of animals that have short necks and round head. The example of Hyracoidean is hyraxes. “They have three toes on their hinds and five of the feet. They haves hooves in their first and the third toe” (1). “The animals that are found in order Scandentia include tree shrews and elephant shrew. They have long tails, a pointed nose as well as the sharp curve” (2). “The examples of animals that are found in Order Sirenia are manatees and dugongs. Scandentians have flippers for front limbs and a flat tail. They have thick bristles on their lips” (1).

Order Rodentia include animals such as “mice, squirrels, chipmunks, rats, voles and beaver. Rodents are small animals that gnaw. Both the upper and lower jaw consists of sharp incisors. Proboscidea is the Order which have animals of great size. They have upper incisors that are tusk, upper lip form proboscis, thick skin, scants hair. The example of Proboscidea includes elephant. They are animals of great size, nose and upper lip form proboscis” (2).

Animals that are found in Pilosa are sloths and armadillos. “They have large claws which are used for digging. Order Primates include monkeys, humans, lemurs and marmosets. Animals of this Order have opposable thumbs, Flat nails on their toes and fingers. In front of their face, they have forward-facing eyes” (1).

“Order insectivores include shrews, moles and hedge dog. They are small animals that use hearing and smell more sight to find prey” (1). “Perissodactyla is small order of herbivores which is comprised of species such as horse, zebra, donkeys, tapirs and rhinoceros. They have odd toes, hoofed form and lack gall bladder” (2).

The animals that belong to order Cetacea include whales, dolphins and porpoises. "Cetacea have bodies that are adapted for water but they are still air- breathing mammals that sticks their nostrils on the water every once in a while or they will drown" (4). "Cetacea have torpedo-shaped bodies, forelimbs that have been modified flippers and tails that are flattened side to side to become flukes" (1).

Reference:

1. NHPTV.Mammals. [Internet] Nature works; 2006 May 24, 11:04 UTC [Cited 2006 May 26]. Available from: http://www.nhptv.org/natureworks/mammalia.htm#16

2.Class Mammalian. [Internet] May 24, 11:04 UTC [Cited 2006 May 26].Science Available from:http://www.cartage.org.lb/en/themes/Sciences/Zoology/

3. Theodore R. Animal Skulls. [Internet]; 2006 May 24, 11:04 UTC [Cited 2006 May 26]. Available from: http://www.animalskull.com.pdf.mascroscelide-dermoptera/

4. Wikepedia Contributors. List of Placental mammals, The free Encyclopadia [Internet] 2006 May 19, 08:30 Available: www.en.wikipedia.org/wiki/placental-mammal

5. Wikepedia Contributors. Placental mammals, The free Encyclopedia [Internet] 2006 May 19, 08:30 UTC [Cited 2006 May 08] Available from: www.en.wikipedia.org/wiki/placentalia

6. Wund, M. and P. Myers. 2005. Mammalia [Internet]. 2006 May 19, 12:17 UTC [Cited 2006 May 08] Available from: http://animaldiversity.ummz.umich.edu/site/accounts/information/Mammalia.html.

Masiya Kedibone
CSIR Pretoria
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Cell No: 073 2519071
Tel No: 012 8412123
Fax: 012 842 3676
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REASONS WHY HERBIVORES DIET IMPOSES CERTAIN PROBLEMS FOR DIGESTION AND ANSWERS ON HOW SOME ANIMALS HAVE OVERCOME SUCH PROBLEMS

Herbivore “is an animal that is adapted to eat primarily plant matter (rather than meat)” (1). They can be classified into different sub-groups which include “the frugivores, which eat mainly fruit; or folivores, which specialize in eating leaves” (1).

Different plant foods are available differently depending on the variations of the seasons. As a result their diets tend to be different for example “in the temperate zones, where different plant foods are most available at different times of year” (1). “Many herbivorous animals that live in the temperate zones change their diet at different seasons of the year. In some places, some seasons are very rainy and wet, and others are very dry. Animals that live in these places may also change their diets at different seasons” (2).

There are the ruminants and non ruminants herbivores. “A ruminant is any hooved animal that digests its food in two steps, first by eating the raw material and regurgitating a semi-digested form known as cud, then eating the cud, a process called ruminating” (3). Goats, sheep, camels and girraffes are examples of ruminants. The stomachs of the ruminants are divided into four chambers i.e rumen, reticulum, omasum and abomasum.. “In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud (or bolus). The cud is then regurgitated, chewed slowly to completely mix it with saliva, which further breaks down fibers. Fiber, especially cellulose, is broken down into glucose in these chambers by symbiotic bacteria and protozoa” (3).

The non-ruminants (elephants) “digest carbohydrates, protein and fat by enzymatic action” (4). They can tolerate a diet of higher fibre content and lower nutritional quality. The non-ruminant has a lower digestive efficiency than ruminants and therefore a more rapid passage. The ruminants can take more food per time unit than a ruminant.
http://www.hullhorsehaven.com/EquineDigestion.html


They vary of diets in these classes of herbivores poses some problems. These problems are normally seen during digestion. Some of the animals are unable to digest completely the food they eat. Cellulose is another source of problem and it contains much of the energy. Since most of the herbivores digest food through enzymes, therefore it is difficult for the enzymes to be broken down as it contains high organic substances. This cellulose composed of organic substances. only mechanical means such as extended chewing or fermetation can help to speed up the process of digestion.
http://www.knowledgerush.com/kr/encyclopedia/Herbivore


However some animals overcome this problem through a quite a number of different ways. For instance ruminants able bring back food they ate to their mouth from their stomachs and chews again. “The rumen serves as a large vat in which the food, mixed with saliva, undergoes extensive fermentation - a slow decomposition of organic substances induced by micro- organisms. These micro-organisms are responsible for the breakdown of cellulose, the breakdown products becoming available for further digestion” (5)

“The fermentation products (mostly acetic, propionic, and butyric acids) are absorbed and utilized; carbon dioxide and methane (CH4) formed in the fermentation process escape by belching (eructation). Rumination, evident as "chewing the cud", involves the regurgitation and re-chewing of undigested fibrous material, which is then swallowed again. As the food re-enters the rumen it undergoes further fermentation. Broken-down food particles gradually pass to the other parts of the stomach where they are subjected to the usual digestive juices in the abomasums” (5).

“The rumen protozoans include ciliates which superficially resemble free-living forms such as Paramecium. Several hundred thousand protozoa are found in each millilitre of rumen contents. Many of the rumen organisms have been cultured in the laboratory, and extracts from pure cultures show cellulase activity. The ciliates are obligate anaerobic organisms which must meet their energy requirements through fermentation processes” (5).

Reference:

1. Wikipedia contributors. Herbivore [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 23, 04:06 UTC [cited 2006 May 25]. Available from:
http://en.wikipedia.org/w/index.php?title=Herbivore&oldid=54650035.

2. Wikipedia contributors. Herbivore [Internet]. Wikipedia, The Free Encyclopedia; 2006 Feb 16, 11:51 UTC [cited 2006 May 25]. Available from:
http://simple.wikipedia.org/w/index.php?title=Herbivore&oldid=101801.

3. Wikipedia contributors. Ruminant [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 22, 23:58 UTC [cited 2006 May 25]. Available from:
http://en.wikipedia.org/w/index.php?title=Ruminant&oldid=49674058.

4. Wright, B. Equine Digestive Tract Structure and Function; 2006 May 03 UTC [Internet] [Cited 2006 May 25] Available from:
http://www.hullhorsehaven.com/EquineDigestion.html

5. The gastrointestinal system, An introduction [Internet] [cited 2006 May 25]. Available from: http://www.chu.cam.ac.uk/~ALRF/giintro.htm

Mr Lufuno Mukwevho
CSIR Pretoria
P.O. Box 395
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WHY HERBIVORES IN THE FOREST LIVE ALONE OR IN PAIRS, WHILE HERBIVORES IN OPEN GRASSLAND LIVE IN GREGARIOUS GROUP

Herbivores are animals that depend on plants for their survival. Herbivores can be classified or divided into groups such as fungivores and folivores. Fungivores are animals that feed themselves on fruits and folivores are animals that feed themselves on leaves. Most of the animals that eat fruits, they also eat plants, roots and seeds. Herbivores animals use open grassland and tropical rain forestas their dwelling place. Forest is the large area of trees which grow close together. It also have plants, shrubs, herbs and grasses. The dominante species are tall trees such as Acaccia species etc with a dense canopy. Grassland is the area or the land covered with wild grasses such as rooi grass ect, shrubs, tress far away from each other. The dominant species are grasses.

Herbivores that are found in both open grassland and forest environment include insects such as grasshoppers and many other insects which are living in the dapple shade of the forest. Other herbivores include" birds such Ross’s turaco which depend on dense cover or vegetation and the large and small animals such as elephant, gorillas, pygmy hippo, bongo, okapi, zebra, giraffe, rhinoceroses, hippopotamuses, rabbit and hares etc”(1,2). All these animals depend on fallen fruits, seeds, sapling, twigs, shrubs, leaves, flower etc for their survival. ( Wikipedia contributors, 2006).

Zebras are one of the herbivores that are found in open grassland environment. These animals preferred to live in gregarious groups, it is simple and easy for them to communicate to each other if their enemies are close to them. Zebras feed themselves on grass for their survival. Living in social units helps the grassland animals cover more area with their eyes so that they can find their food and their predators faster. The other things that protect zebras from their enemies are their stripes which confuse their predators during the attack. There is no enough space to hide in open grassland; herbivores have to use speed to escape from their predators (Wikipedia contributors, 2006).

Another example of the herbivores found in the forest is giraffes. These animals have long neck to reach leaves about the floor or on the high canopy of the trees. They are found in tropical rain forest which have warm temperature. They have stripes legs which help them the blend into the shadow of the forest. Giraffes live in pairs and are not easy for them to see their enemy and they are not easily to be killed because they are big animals. They do not want to live in group because most of the animals feed on leaves they are scared that there will be a shortage of leaves that is why they preferred to live in pairs (Wikipedia contributors, 2006).

Okapi animals are found in forest and they live in pair. They feed on "the foliage which is avoided by other forest animals" (1,2). Animals such as deer are also feed on foliage but they live in a gregarious group compared to the okapi. It is simple for the herbivores that are found in forest to hide themselves from their enemy compared to those herbivores live in grassland; they have the chance the run to the tress as some of them are using trees as their living place (Wikipedia contributors, 2006).
Duikers are found at rain forest and they feed on fallen fruits and seed. Bird such as Ross’s turaco etc is herbivores that depend on dense cover or vegetation in order to protect themselves from their predators. The other herbivores that are found in grassland are grasshoppers, rabbit, snails and slugs. Malay tapir is a largest species which related to horses and rhinos. Tapir feeds on grass, leaves and fallen fruits and it lives alone or in a pairs because it does not want to be disturbed by other animals (Wikipedia contributors, 2006).

Herbivores that are found in open grassland can run fast away from their predators compared to those herbivores found in forest. Since there is no enough space to hide in grassland, living in social units help them to cover more area with their eyes so that they can see their predators faster and run away. Herbivores found in forest live alone or in pairs are selfish because they do not want to share their food with other animals, they want to eat alone.

Reference:

1. Whiet, P. Wendy Vanasselt. 2006. Pilot Analysis of Global Ecosystems: Grassland Ecosystems [ Internet]. Accessed 2006 [cited 24 May 2006, 15:45]. Available from:
http://earthtrends.wri.org/features/view_feature.php?theme=7&fid=5

2. Wikipedia contributors. Herbivores [Internet]. Wikipedia, the free encyclopedia 2006 May 30, 00:26 UTC [Cited May 12, 12:45]. Available from: http://en.wikipedia.org/wiki/Herbivorous




Lizzy Maluleke
CSIR PTA
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Cell number 072 351 8488
Tell [012] 841 2133
Fax [012] 842 3676
E-mail mmaluleke@csir.co.za
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ECHOLOCATION IN BATS AND WHALES

Echolocation is the skill to see through sound. The good examples of animals that use echolocation are bats and whales. Those animals use ultra-high frequency sound for navigation. To understand how echolocation works, imagine an echo-canyon. If you stand on the edge of a canyon and shout, hello!! you will hear your own voice coming back to you an immediate later. Animals that use echolocation release calls out to the environment. Echolocation is the method of sensory awareness. By using echolocation animals can communicate with others using echolocation methods and they can also know animals surrounding that areas. Animals that use echolocation, they use echoes to locate, to range and to identify the objects. Echolocation is used in various environments for foraging. Now lets look at bats as an example of animals that uses echolocation.
http://en.wikipedia.org/wiki/Animal_echolocation

Most of the bats use echolocation to find their food. Some they use sound to find food and find the way in the dark. Although Bats emitted high sound. Which means bats can send out high frequency. By sending this high frequency they can listen for the echoes to locate their prey. They send these sound waves by using their mouth and even nose. Then the sound hits an object, echo can comes back and the bats can identify an object by the sound of the echo.

However, most bats see very well. They can also see in the dark by listening to the echoes. They are listening to the echoes of high frequency calls. Because of this system they can catch up the insects and choose one they like." Those bats that can see very well, echolocation can help them to find their prey in the dark. Those bats that eat frogs, fish and insects use echolocation to find their prey”(2). After emitting a sound they use echolocation even in darkness. Because of this process of echolocation it is easy for bats to find the distance and direction. http://www.eparks.org/wildlife_protection/wildlife_facts/bats/echolocation.asp

On the other hands, those bats that eat fruits they do not use echolocation to find food; they use eyesight and smell for finding food. One good examples of those that use echolocation, if you see thousands of bats flying out of cave, they use echolocation of noise. Different bats use different patterns of echolocation.

Whales is an another examples of animals that use echolocation.Whales are large, and are aquatic mammals. Toothed whales used echolocation to sense objects. Toothed Whales also sent out high sound and those sounds are bounches off the objects. The sounds that are produced whales are used to communicate. They use sound by sending out a ray of sound. When the sound of echo came back, those sounds are picked up by the lower jaws. “Remember that, the lower jawbones of whales are fat and are empty and it helps the sound to pass through the jawbones to the middle ear and auditory nerve”(1).Whales sent out high-pitched sound. The sound bounches off, and then object and some returns to the whale. This returning echo to determine the object shapes direction, distance and texture.
http://www.whaletimes.org/echolocation.htm

They are some whales that do not use echolocation but it may either find their prey by listening. Some toothed whales prey on fish, and marine mammals. They prey on fish using echolocation. Remember that echolocation helps an animal to navigate in water. Finally, the highest sound produces a more detailed of an object to animals that use echolocation because the sound wave is shorter. The opposite is the same. A lower sound travels into water because the wave’s length is longer and can be used to detect distance or larger objects. Water is an excellent sound transmitter. “Whales have capitalized on this water to compensate for reduced visions in cloudy water of the sea”.(3)

References

1. Wikipedia contributors. Echolocation [Internet] Wikipedia, The Free Encyclopedia 2006 May 07, 18: 16 UTC [cited May 15, 16: 10]. Available from: http://en.wikipedia.org/wiki/Animal_echolocation
2. Roth, J. 2006. Echolocation. [Online]. Available: http://www.eparks.org/wildlife_protection/wildlife_facts/bats/echolocation.asp [2006, May 14]
3. Max, J. 1995. Fishin for facts: Echolocation. [Online]. Available: http://www.whaletimes.org/echolocation.htm [2006, May 14]

4. Wikipedia contributors. Echolocation [Internet] Wikipedia, The Free Encyclopedia 2006 May 13, 00: 49 UTC [cited May 15, 16: 10]. Available from:http://en.wikipedia.org/wiki/Whale

Linette Netshiheni
CSIR
Pretoria
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Cell: 0820446442
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tnetshiheni@csir.co.za
Weblog: http://tnetshiheni-linette.blogspot.com/

BIRDS ARE THE LIVING RELATIVES OF DINOSAURS

The birds are the phylum chordate, from the class Aves. They are the avian dinosaurs and theoretically considered as reptiles. The birds descended from diapsids dinosaurs. The earliest species of the class Aves to be known was Archaeopteryx. They are characterized by “the bony beak without teeth, the laying of hard – shelled eggs, high metabolic rate and a light strong skeleton” (1). The most important characteristic of the bird is flight or that they fly (2).


The dinosaurs were the subphylum of chordates, specifically, those with “backbones or spinal columns that conquered the terrestrial ecosystem over 160 million years” (3). The dinosaurs were a group of diapsids reptiles that firstly evolved from archosauriform ancestor during “the olenekian, like modern crocodilians” (3). They firstly appeared about 230 million years ago, and became extinct 65 million years back at the time of cretaceous. After their extinct they were no longer dominant on land. “The clade maniraptoran is the group of the theropod dinosaurs that many paleontogists believe birds were derived from some 150 or so million years ago, in the Jurassic period on the other side of the phylogenetic taxonomy birds are by definition maniraptoran and other maniraptoran are their closest relatives” (3).


The birds are the direct descendants of meat eating dinosaurs (eoraptor). However, the dinosaurs are not birds or reptiles at all. The dinosaurs are having straighter legs. They had unique movement, “walked with their legs underneath them” (1). The little dinosaur meat-eaters were probably the ancestors of birds. The dinosaurs also laid eggs, even though their eggs differ somewhat from those of birds, and at least some dinosaurs nested in colonies and cared for their young in the nest as the birds do, they take care of their young one until they are able to fly on their own” (2).


The birds and the dinosaurs were somehow comparable. The birds have hollow bones, and so did pterosaurs. Dinosaurs walked upright as birds do. The meat-eating dinosaurs had very similar skulls to birds. Some of the smaller dinosaur had bodies and arms that are similar to birds. The first bird known as, archaeopteryx, looks the same as the small meat-eating dinosaur. The different between the archaeopteryx and the small meat eaters was the feathers (1).


The birds share many characteristics with their extinct relatives and those characteristics enable them to fly. The birds have evolved remarkable specializations for flight. They resembled the flight from the Ornithomimids and other small theropods. They also resembled a unique breathing system, light yet strong hollow bones. They resembled a skeleton in which many bones are lost and “powerful flight muscles and -- most importantly – feathers” (2).


References:

[1]. Dinosaurs. TM & © 2006-1996 Scholastic Inc. All rights reserved, 10/05/2006, 09:00. Available from: http://teacher.scholastic.com/researchtools/articlearchives/dinos/evolut.htm.

[2].The link between birds and dinosaurs. 10/05/2006, 09:40. Available from: http://learn.amnh.org/courses/dinosaurs.php.

[3].The wikipedia contributors, Coordinated Universal Time [Internet], Wikipedia, The Free Encyclopedia; 2006 May 10, 10; 00 UTC [cited May 2006]. Available from:
http://en.wikipedia.org/wiki/Dinosaurs.


[4].The wikipedia contributors, Coordinated Universal Time [Internet], Wikipedia, The Free Encyclopedia; 2006 May 10, 11; 00 UTC [cited May 2006]. Available from:
http://en.wikipedia.org/wiki/Phylogenetics.


Ms Evelyn Maleka
CILLA CSIR
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Pretoria, 0001
Tel: (012) 841 2133
Fax: 012 842 7024.
Email: emaleka@csir.co.za
http://malekaevelyn.blogspot.com/

BIRDS HAVE BEEN DESCRIBED AS THE LIVING OF THE RELATIVES OF DINOSAURS

Dinosaurs and birds are vertebrate animals that are found on land or terrestrial environment. These two species are omnivores meaning that they feed themselves on plants, meat seeds and fruits from the trees. Dinosaurs have four legs and they do not have wings. The birds have legs and wings which are used fly. Both birds and dinosaurs have back bone. The evidence that the paleontologists have about the close relationship between the dinosaurs and birds is unclear or controversial. It is because some paleontologists believe that dinosaurs are ancestors of birds resemble to dinosaurs. Paleontologists made their decision suggesting that birds are living relative of the dinosaur’s species.


Some Paleontologists suggested that recorded fossil of birds and dinosaurs. Indicates that there is a closely relationship between them. It is said that because a fossil of confuciousornis species in China which was a resemblance of Archaeopteryx species, and this species have wing claws like a modern birds and they had no teeth like the birds. Confuciousornis and Archaeopteryx fossil look like the birds and they did fly like birds.


Some paleontologists came up with the negative thoughts about the relationship between the birds and the dinosaurs and they gave the evidence on the bones. They said that the birds have different number of the toes. They said that some birds have three toes, some have five and some have more toes but depending on the area where they found. It said that some of the bones toes of the birds resemble of the reptiles are ancestors of the birds.


Paleontologists also disagree about the ribcage in the fossils of dinosaurs which was compressed more from back to their belly. Some scientists believe that the similarities between dinosaurs and birds are very imported. They said that by comparing the bones in the wings of birds with the front feet of the dinosaurs. The evidence indicates that these bones are similar to the bones of any other species and birds and dinosaurs had similar behavior.


Some paleontologists believe that birds developed from the reptiles before dinosaurs. They compared birds with the reptiles than dinosaurs, reptiles and birds have many features that they share and which are common in both species. The characteristics of the birds and the dinosaurs include wings with four functional fingers, long bone, slender, vertebrate tail recurved teeth, set in socket and vertebrate biconcave etc are different from those which are found in dinosaurs such as very hallow bones etc.


Birds and dinosaurs look the same because they live in the similar environment and they also did things to survive in a similar way. It is said that the birds live at the same time with the dinosaurs did fly but not as well as a modern birds. It is because of their features which are the same with the reptiles. The features of the birds and dinosaurs are touted as the missing link between them. The relationship between birds, dinosaurs and evolution of flight is more complex. It is because some paleontologists believe that birds developed from dinosaurs where as some paleontologists believe that some dinosaurs developed from the birds.


Reference:


Wikipedia contributors. Birds [Internet] the free encyclopedia, 2006 May 14, 23:56 UTC [Cited 2006 May 14:00]. Available from:
http://en.Wikipedia.org/Wiki/Birds

Wikipedia contributors. Dinosaurs [Internet] the free encyclopedia, 2006 May 15, 04:56 UTC [cited 2006 May 15:23]. Available from:
http://en.Wikipedia.org/Wiki/Dinosaurs


Lizzy Maluleke
CSIR PTA
0001
Cell number 072 351 8488
Tell [012] 841 2133
Fax [012] 842 3676
E-mail mmaluleke@csir.co.za
Weblog: http://mmaluleke.blogspot.com

ECHOLOCATION IN BATS AND WHALES

Bats and whales use high frequency sounds like sonar and radar to locate objects in the surrounding environment (echolocation) (2).

Whales use sound to sense objects especially when they are hunting. Whales make a high-pitched click sound which bounces off the object. Whale starts by producing a series of low-frequency click sounds before they can be able to produce a high-pitched sound. The frequencies pass through the “melon of the whale” (1). The click sound is focused into a ray of sounds and some of the sound bounces off and then returns to the whale. The sound waves which come back are received by the fat-filled cavities of the lower jaw-bone of the whale. The sounds are interpreted through the bone of the ear and the brain. The whales interpret the sound and determine how the object looks, how far and how far the object is (1).

Bats are active during the night so they look for food at night. Bats also use the same process as the whales when hunting (echolocation). Bats produce the sound by speeding up air from their lungs; through their vibrating vocal chords. These vibrations cause fluctuations in the speed of the air, which forms sound wave (3). The change in air pressure pushes surrounding air particles out and then pulls some of them back in. These particles then "push and pull the particles next to them, passing on the energy and pattern of the sound" (3). In this way, sound can travel long distances through the air. The pitch and tone of the sound are determined by the frequency of the air-pressure fluctuations, which is determined by the way they move their vocal chords (3).

Some bats emit the sounds through their mouth and others emit sound through their nose (3). It's not fully understood how the bat's sound production works, but scientists believe that the way the nose of a bat is structured serves to focus the noise for more accurate pin-pointing of insects and other prey. The sounds that bats realise range from 14,000 to 100,000 hertz in frequency (4). In the case of most bats, the sound that they produce is very loud. The sound travels through the air as waves, and the energy of this waves bounces off any object it comes across. A bat listens carefully to the sounds that return to it and interprets information/sounds in its brain. It determines how long it takes for a noise or sound to return to its ears. Then the bats use their brain to figure out how far away is an object, also the shape of an object (3).

The bat can also determine where the object is, how big it is and in what direction it is moving. The bat can tell whether its victim is to the right or left by comparing how fast the sound reaches the right or left ear first: for example if the sound reaches the right ear before it reaches the left ear, then the bat knows that its victim is on the right and vice versa. The bat's ears have a "complex collections of folds that help it determine an insect's vertical position" (3). Echoes coming from below will hit the folds of the "outer ear at a different point than sounds coming from above, and so will sound different when they reach the bat's inner ear" (3). A bat can tell how big its victim is; based on the power of the echo. Small object will reflect fewer sound waves then produce a less powerful resound and bigger objects will produce very powerful resound (3).

Whales use their tooth to locate their objects by producing a click sound while bats use their lungs to make the sounds which is released through the mouth or nose. The mechanism that these animals are using is safer because they can sense how far an object is and they can also tell the direction in which the object is travelling. The mechanism that both the whales and bats are using requires them to listen attentively. They should have good listening skills so if it happens that they become deaf what are they going to do because they depends mostly on their listening skills. If they loss their ability to make sounds or their listening skills does this mean that they are no longer going to eat because they hunt animals by making sounds and listening to the echo.

Reference:

1. Anon .Echolocation –Whale Glossary. [Internet] Updated 2006. Cited 2006 May 16. Available from: http://www.enchantedlearning.com/subjects/whales/glossary/Echolocation.shtml
2. The Georgia Museum of Natural History. Google definition: [Internet] Updated 2000 Jun 30. Cited 2006 May 16. Available from: http://museum.nhm.uga.edu/gawildlife/glossary/gawwglossary.html
3. Anon. How stuff works “How Bats Work”. [Internet] Updated 2006. Cited 2006 May 16. Available from: http://science.howstuffworks.com/bat2.htm
4. Anon. Answers.com. Animal echolation. [Internet] Updated 2006. Cited 2006 May 25. Available from: http://www.answers.com/topic/animal-echolocation

Lethabo Mosomane
CSIR
Pretoria
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Tel: 27 12 841 2133
Fax: 27 12 842 3676
Mail: lmosomane@csir.co.za
http://lmosomane.blogspot.com/

DESRIPTION OF HOW PLACENTAL MAMMALS HAVE COLONIZED LAND, WATER AND AIR

The placental mammals are found to be the largest group of the mammals that comprise about 4300 (2). These types of mammals are biologically classified into nineteen orders. The largest group of these mammals contains the rodents, such as rats, mice, squirrels, and porcupines (5).

The young placental mammals are born at a comparatively advanced period (2). These mammals include elephants, whales, shrews and armadillos, it also includes pets such as dogs and cats remove the quotation marks, it includes also the farm and work animals like; cattle, sheep, and horses. The human beings also form part of the placental mammals (2).


Some of the placental mammals are found on land, water and in the air. They are found with different shapes and body size (2). They also differ in their method of surviving, some are carnivores, and some are omnivores while some are herbivores. The differences are also in those that colonized the land, they live in different shelters, for example: human live inside the house while the sheep and cattle in the kraal, etc. (2). The placental mammals that live on the land are having feet, those who occupied the water are having gills and those who colonized the air are having the wings (3). The seals, including the sea lions and the walruses does not reproduce in the open oceans, however they spend most of their time in the open oceans, and they depend on the land for reproduction (3). The largest plant eating mammals that spend their entire lives in water are dugongs and manatees (4). The only group of the placental mammals to occupy the air were the bats (2).


The whales, including the huge baleen whales and the dolphins, are well adapted as fast, open ocean predators (3). These marine placental mammals are only found in the areas where there are large amount of food, especially where the water temperature is low (3). These mammals survive the cold conditions in two different ways. Some of the placental mammals have very “sparse hair and blubber” (2). These sparse hairs help them to become warm. Other placental mammals have a double coat of fur, with very dense “under fur hairs closely packed” (2) and this prevent their skin from being wet (2).


The majority of the aquatic mammals in the world live in the ocean, yet some live in the freshwater, for example: river dolphins, and otters adapted to life in fresh water habitats. The rodents are found to have successfully occupied the land, air and the water (1). The rodents managed to occupy the air, water and the land because they are small in size and this serve as “their advantage to evade the extreme conditions” (1).


In conclusion, the placental mammals colonized the air, water and the land very successfully. The humans would not colonize the air because of lack of wings, but they colonized the land. The bats colonized the air. The seals live both the aquatic and terrestrial life, they spend most of their time in the water, but they still have to come to land so that they can reproduce.


References: [1]. Wikipedia contributors. Coordinated Universal Time [Internet]. Wikipedia. The Free Encyclopaedia, 2006 May 12, 09:00. UTC [cited 2006 May 15]. Available from: http://en.wikipedia.org/wiki/placenta.


[2]. “Mammal,” Microsoft® Encarta® Online Encyclopaedia 2006 © 1997-2006 [cited 2006 May 12, 10:00].Microsoft Corporation. Available from: http://Encarta.msn.com/encyclopedia_761561349/Mammal.html.


[3]. "Whale," Microsoft® Encarta® Online Encyclopedia 2006 © 1997-2006 [cited 2006 May 12, 1030] Microsoft Corporation. Available from: http://encarta.msn.com/encyclopedia_761565254_6/Whale.html#howtocite.


[4]. Wund, M. and P. Myers. 2005. "Chiroptera" (On-line), Animal Diversity Web. [2006May 12, 11:00]. Available from: http://animaldiversity.ummz.umich.edu/site/accounts/information/Chiroptera.html.


[5]. "Mammal," Microsoft® Encarta® Online Encyclopedia 2006 [cited 2006 May 12]. Available from:
http://encarta.msn.com/text_761561349__1/Mammal.html.

Ms Evelyn Maleka
CILLA CSIR
P.O. Box 395
Pretoria,
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Tel: (012) 841 2133
Fax: 012 842 7024.
Email: emaleka@csir.co.za
http://malekaevelyn.blogspot.com/

VARIATION IN SHELL STRUCTURE OCCURRED IN THE PHYLUM MOLLUSCA

The mollusks constitute one of the largest phyla of animals, both in numbers of living species and in numbers of individuals. All mollusks have a soft body, which is protected by a hard, calcium- containing shell. Mollusks are “triplobastic (ovum which has three primary germ layers-ectoderm (outer), mesoderm (middle) and endoderm (inner layer) protostomes” (1). A significant characteristic of mollusks is their possession of a “coelom, a fluid-filled cavity that develops within the mesoderm” (1). The coelom functions as a “hydrostatic skeleton which also provides space within which the internal organs can be suspended by the mesenteries” (1). The body cavity is filled with blood. Mollusks have a mantle (fold of the outer lining of the shell and a muscular foot that is used for motion-movement). Many mollusks mantle produces a “calcium carbonate-external shell and their gills extracts oxygen from water" (1).

Phylum Mollusca are divided into different classes which have different types of shells:-

· Class Gastropoda

Most of the gastropods have shells, however there are quite a few groups that have either reduced or internal shells, or no shell at all. Although most gastropods are marines, there are “numerous forms in both freshwater and terrestrial environments” (2). Most members have a shell which is in “one piece and typically coiled or spiralled which usually opens on the right side" (2). Some species have an operculum which operates as a door which closes the shell.

· Class Pelecypoda (Bivalvia )

They have two part shells with both parts being less or more regular. The class include scallops, clams, oysters and mussels. Their shells are composed of calcium carbonate and the shells are very strong. In some bivalves the shell is made up of calcium carbonate known as aragonite which is not very strong (3).

· Class Cephalopoda

This class includes species like squid, octopus and cuttlefish. Their shell is either internalized or absent. The cuttlefish is the only cephalopod which has a shell. The shell occupies only the outermost portion of its elaborate and beautiful coelom, the rest of which serves as a flotation chamber. In the squid and cuttlefish, the shell has become an internal stiffening support, and the octopus does not have a shell at all (4).

· Class Monoplacophora

They have a single, flat, rounded bilateral shell which resembles chitons. Their shells are often thin and fragile and their shell apex is forward (5).

· Class Polyplacophora

This class include the chitons which have seven or eight dorsal shell plates embedded in the tough muscular girdle that surrounds its body. Their calcareous armour shell that they carry dorsally acts as a protective measure. Their shell is made up of aragonite and colored (6).


· Class Scaphopoda

They are also called the tusk shells because their shell is openly curved plan spiral tubular shell which opens at both sides and the shell resembles an elephant tusk. They have tapered, tubular shells that open at both ends (7).

Reference:


1. Wikipedia contributors. Mollusc [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 4, 3:39 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/wiki/Mollusc

2. Wikipedia contributors. Gastropods [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 20:07 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/wiki/Gastropoda

3. Wikipedia contributors. Bivalvia [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 19:00 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/wiki/Bivalvia

4. Wikipedia contributors. Cephalopoda [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 03: 04:57 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/wiki/Cephalopoda

5. Wikipedia contributors. Monoplacophora [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 22, 20:03 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/wiki/Monoplacophora

6. Wikipedia contributors. Polyplacophora [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 04, 15:32 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/wiki/Polyplacophora

7. Wikipedia contributors. Scaphopoda [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 23, 12:22 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/wiki/Scaphopoda


Lethabo Mosomane
CSIR
Pretoria
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Tel: 27 12 841 2133
Fax: 27 12 842 3676
Mail: lmosomane@csir.co.za
http://lmosomane.blogspot.com/

THE DIFFERENT METHODS OF REPRODUCTION BETWEEN PLACENTAL AND MARSUPIAL.

The marsupial animals belong to the marsupial order (3). These animals are sharing the class metatheria with the “kangaroo, koala, Tasmanian devil and the Virginia opossum” (3). The female marsupials were found to have being carrying their young ones in a pouch (3). It seems as a pouch is a pocket used by the marsupial to carry their young ones.

The placental are thought to be the one of the group of mammals belonging to “the third subclass of the mammals” (4). They are named placental as the results of their functions, they “connects the growing embryo within the uterus to the circulatory system of their mother” (2). The placenta is the way used for the fetus to get food (3). Before the placental mammals give birth, they take a long process in the growing stage. (3).


It seems as the main different between the marsupial and placental mammals are the rate of gestation. Gestation is the “period that the female keep their offspring in the womb from when they have conceived and when they give birth” (1). It seems as if the process of mating continues in marsupials mammals while in placental mammals stop when they are pregnant and continues after they gave birth (4).

The body of the marsupial mammals are not connected to the embryo (4). It is separated by the embryo protector, amniotic membranes (4). This membrane is known to protect the embryo by separating it from the biological connections with the parent (4). These membrane play an important role, because when “fertilization take place the embryo becomes a new organisms and the immune systems attack it, but because of the protection the attacker becomes unsuccessful” (4).


The more there are few nutrients in the egg there will be few nutrients of marsupial embryo, because “they depends on the egg yolk for their nutrients” (3). The type of “egg yolk reproduced determines the period of gestation of marsupials” (3). It seems as if the marsupial mammals spent short time in reproduction, they can not spend “more than twelve days in reproduction” (3). In the other side the placental mammals takes “weeks and month in reproduction” (3) which is much longer compared to the marsupials mammals (3).


The long period of gestation that occurs within the placental mammals, helps their offspring to be well develop (3). The placenta allows the “nutrients to travel from the mother systems to the embryo and waste are carried out, and this allows the extension of placental maturation (3). The placenta is composed of numerous layers of blood supply; the mother and embryo have their own blood supply” (3).


In conclusion, indeed there are difference mode of reproduction between the placental and the marsupial. During pregnancy of the marsupials the oestrus cycle occurs, while in the placental does not until the whole period of pregnancy is over. The embryo of the marsupial is not connected to the mother while of the placental is connected. The marsupial gives birth very fast as compared to the placental. The main difference between the marsupial and placental mammals is their rate of gestation.

References:


[1]. A Creation Theory into the Origin of Marsupials. [http://nwcreation.net/marsupials.html, accessed on 12/05/2006, 08:00].


[2].The wikipedia contributors, Coordinated Universal Time [Internet], Wikipedia, The Free Encyclopedia; 2006 May 12, 09; 00 UTC [cited May 2006]. Available from: http://en.wikipedia.org/wiki/placenta.


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