Biodiversity

Wednesday, May 10, 2006

ECHOLOCATION IN BATS AND WHALES

Echolocation (biosonar) is a method used by animals (mammals) like bats, whales and dolphins to locate objects or other organisms. These animals emit sounds (calls) out to the environment and then listen to the echoes returning from various objects in the environment. They use these echoes to locate, range and identify the objects1. The word BIOSONAR comes from the words BIO-life and SONAR -"SOund Navigation And Ranging"2. It’s used for in underwater for location of other vessels (objects) and navigation2. For the mammals it’s used for navigation and hunting1.

The first fossil of fully developed bats was dated 50 million years ago, meaning that the evolution of bats was earlier during the evolution of placental mammals4. Bats are mammals that have their fore limbs modified to become wings and are the only flying mammals. Most bats (70%) feed on insects while others feed on fruits and their juices while others are carnivorous3. Most bats are nocturnal (fly at night) and use echolocation to be able to navigate4. A flying bat has the ability to use sounds of between 50 000 and 200 000 vibrations per second sending out emitting the sounds at short bursts4. They send out these sounds every twenty or thirty times in every second and has so great hearing power that from the echo produced by the signals bouncing on an object, the bat can judge the position of the object(s) around it and how fast the prey is moving if flying4. Most bats first receive the echo of a signal before emitting another one. As the distance between the bat and an object reduces, the duration of the echo bouncing back reduces. By increasing and reducing the number of sounds emitted the bat is able to track down the prey with great accuracy1, 4.

Food in the mouth posses a challenge to the bat as it can lose the use of its senses and be not able to emit sounds4. Bats have evolved a way of overcoming this by emitting sounds through their noses that have structures which concentrate the stream of sound acting like small megaphones4. Bats ears are quite sensitive and are adjusted in a way to pick signals. The face of a bat thus looks like sonar equipment, nose has large protrusions for sending and picking signals, plus elaborate ears to pick the signals4. The patterns in the nose and the ear are conspecific so each an every species produce its own unique call. The receptors are able differentiate particular sounds being able to pick out signals from other bats and be able to avoid them even in the dark4. Even though bats have managed to use this method to hunt there are other animals that are able to counter this mechanisms and escape them. In America there’s a moth able to pick the sounds of bats and when they hear bats coming they perch to the ground while others make diving movements which the bats can’t. Dogs too have the ability to detect vampire bats approaching and escape being preyed on4.

Whales use biosonar as they live in water where vision can be impaired by water turbidity and absorption of light rays1. Toothed whales produce a focused beam of high-frequency emissions towards the direction that their heads are facing. Sounds are generated by blowing air out of the bony nares via the phonic lips. These sounds bounce off the dense concave cranium bone in addition to the air sac at its base. It’s modulated by the large fatty organ referred to as the 'melon'1. The clicks in most toothed whales are usually in a series, with the sperm whale producing individual clicks1. In a similar way as the bats the whales are able to not only identify an object but also with the quality of the echo, the type of obstacle ahead. Echo is picked by the lower jaw and transmitted by a fat layer to the inner ear1. Like bats, when whales approach a target they reduce the noise and so reduce the echo’s strength to protect themselves from strong echoes1.

This way bats and whales are able to adapt to find direction and hunt for prey in an environment that would otherwise be unfriendly to them.

References:
1. Wikipedia contributors. Animal echolocation [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 7, 18:16 UTC [cited 2006 May 9]. Available from: http://en.wikipedia.org/w/index.php?title=Animal_echolocation&oldid=52012189.
2. Wikipedia contributors. Sonar [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 9, 03:58 UTC [cited 2006 May 9]. Available from: http://en.wikipedia.org/w/index.php?title=Sonar&oldid=52261714.
3. Wikipedia contributors. Bat [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 8, 03:58 UTC [cited 2006 May 9]. Available from: http://en.wikipedia.org/w/index.php?title=Bat&oldid=52191376.

4. Knight, R. BCB Biodiversity chapter 2 Theme and Variation

(Cited 2006 May8) http://planet.uwc.ac.za/nisl/biodiversity/Chapter2/page_202.htm





VINCENT MUCHAI WAIRIMU
Biodiversity and Conservation Biology
University of the Western Cape
Private Bag X17 Bellville

TEL: +27825103190

Email: 2648463@uwc.ac.za

Website:http://www.muchai.iblog.co.za

MORPHOLOGICAL DIFFERENCE BETWEEN CARTILAGINOUS AND BONY FISH

Cartilaginous fish includes fish such as shark skates and rays. Shark is big. Shark has very strong teeth. Cartilage fish consists of dense connective tissues. It is also have cells which composed of Chondrocytes. This type of cartilage fish has fibre which composed of collagen and elastic fibres. Because of big teeth, it is easy for shark to break pray or to catch pray. Shark is the latest hunters of the oceans. Let’s look at Rays and Skates. These two are quiet or non-aggressive. The bodies of Rays and Skates are large. They also have wings. These wings help them to move smoothly through the water and they use tail as a wheel. Both Rays and Skates are bottom feeders. http://www.biologyreference.com/Bl-Ce/Cartilaginous-Fish.html

Although cartilage has strong jaws. The mouth of cartilage is found on the underside of the body. Where as the eyes of cartilages are found on top of the body. It is not easy for cartilage to see food. Some shark they use nose to touch their food, while on the other hand others use powerful electro sensory system to find food. Sharks, Skates and rays have rough skin. On each side of head shark has 5 to 7 gills slits. Where as Bony fish have 1 gill on each side. Chimaeras or Gost sharks’ skins are smooth and have only one pairs of external gill openings. Cartilage fish give live birth and Bony fish produces eggs. Cartilage fish lives in only salt water while bony fish lives in all types of water. Let’s look at bony fish. http://en.wikipedia.org/wiki/Cartilaginous

Bony fish is a fish that is made out of cartilage. Their liver is filled with oils and these oils keep them from sinking. Bony fish have hard cartilage for skeleton. The bony fish are classified into Lobe finned and the Ray –finned. Lobe-finned bone fish includes fish such as lungfish and coelacanth’s, where as Ray-fins includes the goldfish, tuna, and trout.
Bony fish is true fish, such as snapper, groper and gurnard. They have a bony skeleton and single pairs of external gill openings. The mouth of bony fish is found on the front of the body and they also have a tail fin, which are found on the top and bottom portions nearly the same size. Bony fish has short tube. In terms of fertilisation, bony fish reproduce by external fertilization of eggs and they release them into water. The male releases sperm. Those sperm that are released by males are called Milt. http://www.biologie.uni-hamburg.de/b-online/library/crone/3051/highli05.html

Finally, the bones of fish have calcium but Shark does not have any bones. Shark skeleton is made of cartilage, and have no bladder, but bony fish have a gas filled swim bladder which enables them to float in the water. Bony fish have movable parts were as shark does not have. Shark can turn around in a smaller space than bony fish.
On top of shark it is dark in colour which is called dorsal side, and light colour on the bottom which is called ventral.
Shark have noses that use for smelling, not for breathing one can find their pairs of nostrils on underside of their snouts. The eyeball of shaka is cornea, iris, pupils, lens and retina. Shark teeth are parallel. http://www.biology4kids.com/files/vert_fish.html

Reference

1. Studios, A.R. 1997-2006 Biology for kids’ vertebrates’ fish [Online].Available from:
http://www.biology4kids.com/files/vert_fish.html [2006, May 09 13:00]

2. Gale, T. A part of the Thomson corporation, 2006. Cartilaginous fish, [Internet]. Online [Access:2006 May 09 12:30] Available from:http://www.biologyreference.com/Bl-Ce/Cartilaginous-Fish.html

3. Hudson Valley Community College, 2000,life in the water, [Internet] Online. Access: 2006, May 09 14:00] Availible from:
http://www.biologie.uni-hamburg.de/b-online/library/crone/3051/highli05.html

4. Wikipedia contributors. [Internet].wikipedia, The free encyclopedia, 2006 May 09, 10:03 UCT. [Cited May 09] Available from:http://en.wikipedia.org/wiki/Cartilaginous

Linette Netshiheni
CSIR
Pretoria
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Cell: 0820446442
Tell: 012 841 2133
Fax: 012 842 3676
tnetshiheni@csir.co.za
Weblog:
http://tnetshiheni-linette.blogspot.com/

THE EVOLUTIONARY TRANSITIONS FROM THE EARLIEST CHORDATE (E.G. AMPHIOXUS) TO THE MOST ADVANCED BONY FISH

Fish have various groups, which is made up of three living classes that hold an important place in evolution history and modern ecology. Fish are the first known vertebrate (animals with backbones) and also the first species that evolve in land –walking vertebrates, they are the first known true chordate that has been found. (1)


It was suggested that fish evolve before the Devonian periods which was referred as the Age of fishes, fishes where aquatic species. Then at the end of Devonian periods tetrapods (vertebrate) which evolved legs which they can be used to walk on land evolve, and this evolution led to the adaptation to land in the form of amphibians.(1)


Ostracoderms was the first fish to evolve in the period of Cambrian about 510 million years ago and became extinct at the end of the Devonian periods it was jawless fishes found in the aquatic environment, it was covered by scales this Ostracoderms were less than 30cm long and it was placed in the class of Agnathans. These jawless fishes were the first vertebrates. Jawless fish was having circular mouth with a sharp spine tongue which is used for sucking and filtering food. Most of the species under this class agnath was not having fins except for a fringe around the tail, And they possesses the beginning of the backbone in a form of cartilaginous. (3)


In agnath group they were other small fish like animal which possessed heavy protective covering –plating, this was originated from the deposit of salts from food they eat. This plating was suggested that it tend to harden the gill arches to become the upper jaw and the bottom gill into lower jaws. And this evolution of jaws on fishes was important because it permit the fish to feed on variety of foods. Having jaws allowed them to be vigorous hunters as opposed to passive filter feeder. Being vigorous hunters led the fish to have large diversity of adaptations.(3)

This salt deposit marks the first presents of bone in the fishes which influence the evolution of vertebrates. The bony plate provides protection against sea scorpions that co-existed at the same time.(1)

Some of the bony scales in the skin around the mouth enlarge and became first teeth, while the lateral flaps of skin evolved into true fins which improve the swimming. Because of the food they eat with salts, lots of features evolved other develop some back bones. Species such as Acanthodii develop internal bony skeleton running longitudinal through the body. And this type of species was likely the ancestor of the bony fish we know today. (3)

Bony fish are often regarded as "true" fish. This group includes most of the fish we are familiar with to day. They are characterised by short jaw with lower jaw articulates with vertical quadrate it also have symmetrical caudal fin for swimming. They also have bony skeleton and single pair gill opening this are the advance bony fish we have today in the class of vertebrate. (2)


In general there is much to be learned from fish, they have evolved to fill every aquatic and inland environment with variety of adaptation. Fishes are important in evolutionary steps they are the first known vertebrate and also influence the evolution of all living vertebrate on land.

Reference:


1. Kagle R.1997.The Evolutionary Steps Of Fish [internet] [cited 2006- May -08] Availablefrom:http://serendip.brynmawr.edu/biology/b103/f97/projects97/Kagle.html


2. Fish Distribution [Internet] [cited 2006-May-08] Available from: http://www.lookd.com/fish/distribution.html
3. The Major Radiation of Fishes;[Internet][ cited 2006-May-08] Available from:http://users.tamuk.edu/kfjab02/Biology/Vertebrate%20Zoology/b3405_ch08.htm

4. Wikipedia contributors. Osteichthyes. [Internet] Wikipedia, the Free Encyclopedia; 2006 May 07. [Cited 2006-May-08]Available from: http://en.wikipedia.org/wiki/Osteichthyes



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://www.emuanalo.blogspot.com

REASON WHY AMPHIBIANS AFTER EVOLVING LIMBS THEY BECAME LIMBLESS

Amphibians are grouped in phylum chordate, subphylum of vertebrate and class amphibian. These Vertebrates comprise of many living chordates, and they have evolved an enormous variety of forms. This is divided into eight classes; four are aquatic which is grouped into super class Pisces, while four are terrestrial. They are grouped as super class Tetrapods or four-footed animals.

They have different movement aquatic species like fish moves by weaving of the trunk and tails, "most of them have sets of paired fins pelvic and pectoral they do not have limbs".(1) The terrestrial species move in the form of wriggling which is similar to those of fish even though it has limbs that support the movement.

Some have limbs that make movement simple, like Frogs and toads use their muscular hind legs for jumping. While other amphibians have lost their limbs and most of that species are burrowing forms. (1)

"As evolution are taking place basic forms of structure evolve to perform number of task, example tetrapods, forelimbs becomes used for grasping climbing, flying, burrowing and swimming as well as terrestrial locomotion. In amphibians, limbs improved for locomotion. These evolve into upright position which is different to what amphibian have of sprawling, and have some tendency towards bipedalism among reptiles and birds". (1)


All these changes in limbs evolve from fish and the vertebrates that start to evolve on land it was suggested by scientist that many of limb and muscles developments needed for walking on land before fish and limbed animals split.


When Tetrapods moved onto land they lose connection between the skull and the pectoral girdle as they move on land. The pelvic girdle became closely involved with vertebral column using the sacral vertebrae. While in fish the pelvic is made up of one and basiterygium (paired bone). In amphibians, the basiterygium divided into the ilium and ischium. Because the pectoral girdles are not attached to the head of terrestrial animal no force of walking can be send directly into skull which shocks the brain. Amphibians did not obtain the strong girdles like fish, because they evolved from fish.

Loss of limbs is very common in all lineages of vertebrates, this because fishes and amphibians, has evolved many times and they all move by the use of the limbs. While if mammals or archosaurs were to lose their limbs, their axial muscular would still be weak and unable to support the animal. (2)


Only one group of mammal (whales) have ever lost either of the limbs. Whales develop a larger, broad tail which is considerably strengthened their axial muscular. "Whales and snakes are animals which have lost limbs and are still retain some element of the girdles".(2)


In conclusion changes in adaptation tend to evolve in the change of structural patterns of the species, this result because some of the species live in both environment and they would like to have features that will allow them to move. so evolving of limbs in amphibians and vanishing of limbs are also influenced by the environment that they choose to live in,


Reference:

1 Limb evolution [internet] [cited 2006-May-09] Available from: http://sellers.sbc.man.ac.uk/~wis/lectures/limb-evolution/LimbEvolution.html


2. Amphibians [internet] [cited 2006-may-09] Available from: http://web6.duc.auburn.edu/academic/classes/zy/0301/Topic9/topic9.pdf


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

EVIDENCE SHOW DINOSAURS WERE WARM-BLOODED ANIMALS

The oldest types of dinosaurs were discovered in Brazil. Some scientists think that, very big dinosaurs could have warm bodies. They are argument among many scientists. Some scientist said that, dinosaurs were warm blooded animals while other scientist said that, dinosaurs were cold blooded animals. Dinosaurs have the ability to control body temperature and maintain it at a constant value. This is the main good advantage that dinosaurs were warm blooded animals(2). E.g. birds and mammals. Some scientist said so because paleoanthropologists think that all dinosaurs were warm blooded animal as modern mammals and birds because they have same metabolic rate. http://www.priweb.org/ed/ICTHOL/ICTHOL04papers/13.htm

Evidence of fossils found in Australia and Antarctica shows that, dinosaurs were warm blooded animals because they can survive in cooler conditions. Although warm blooded animals ate many food. They ate much food in order to provide energy and produce heat. Another evidence of fossils that were found about 230 million years ago, indicate that, dinosaurs were vertebrates animals and the body and characteristics of dinosaurs shows that, dinosaurs were warm blooded animals. Most of the dinosaurs had similar behaviour of birds. According to the scientist, birds are warm blooded animals; it means dinosaurs were warm blooded animals. One can say so, because dinosaurs were more closely related to birds than reptiles. http://en.wikipedia.org/wiki/Dinosaurs

Richard Owen is the one who named the dinosaurs. He said that, dinosaurs were like reptiles. It is also said that, reptiles were very active and are warm blooded animals. Even now scientist who followed Owen classified dinosaurs as lizard.
Assessment of dinosaurs fossils propose that, dinosaurs were warming blooded. Scientist reasoned said, any animal that growing faster must be warm blooded animal, remember that dinosaurs grow fast. The assessment indicates that, warm blooded animals have vascularized bones tissues. Evidence indicates that, dinosaurs have highly vascularised bones. Evidence of bones and footprints support that, dinosaurs are warm blooded animals.

Shower and Berick comes with the evidence of dinosaurs bones. Isotopes from dinosaurs show that, dinosaurs were warm blooded animals. The bones provided by Shower and Berick indicate that, these bones were composed of minerals, calcium phosphate and the oxygen occurs in the form of isotopes. Because of this evidence provided by these two man, they believed that, dinosaurs were warm blooded animals. The bones of dinosaurs are rich in halversian canals. This halversian canals support nutrients from the blood to the cells.http://www.txtwriter.com/onscience/Articles/dinoblood.html

“Some scientists think that very big dinosaurs could have had warm bodies because of their large body size, just as some sea turtles do today. It may be that some dinosaurs were warm-blooded. The problem is that it is hard to find evidence that unquestionably shows what dinosaur metabolisms were like.” (1). Palaeontologist discovered the evidence fossils of dinosaur’s heart. The heart was discovered in the Northern part of South Dakota and they were discovered in 1993. The hearts has 4 chambers which is similar to birds. The heart shows that, dinosaurs were warm blooded animals. Some dinosaurs were carnivores, herbivores and omnivores. The scientists said that, feathers of dinosaurs were not useful for flight. Feathers of sinosauropteryx indicate that, dinosaurs were warm blooded animals and they used feather to retain heat. http://unmuseum.mus.pa.us/colddino.htm

References
1. Ronald J., Robert E. Weems, and Thomas R. Holtz, Jr, Were dinosaurs warm blooded animal? [Online]. Available from: http://pubs.usgs.gov/gip/dinosaurs/warmblood.html[2006 May, 11

2. Beverly, E. 2000. Dinosaurs v.s. Warm-blooded?. [Online]. Available: http://www.priweb.org/ed/ICTHOL/ICTHOL04papers/13.htm%20[2006, May 10]
3. Wikipedia Contributors, Dinosaurs [Internet]. Wikipedia, The free encyclopedia, [cited 2006, May 10]. Available from:http://en.wikipedia.org/wiki/Dinosaurs
4. George,J. 1997. The isotopes in their bones suggest that dinosaurs were warm blooded [Internet] 2006 May, 09 14:30 UCT [cited 2006 may 10] Available from:http://www.txtwriter.com/onscience/Articles/dinoblood.html
5. Kreystek, L. 1996. Hot and cold running dinosaurs [Online] 2006 May, 17 ,15:06 UTC [Cited 2006 May 10]. Avalable from:http://unmuseum.mus.pa.us/colddino.htm

Linette Netshiheni
CSIR
Pretoria
0001
Cell: 0820446442
Tell: 012 841 2133
Fax: 012 842 3676

DISCUSSION OF BIRDS AS THE LIVING RELATIVES OF THE DINOSAURS

The idea that birds have the close relationship with the dinosaurs remains a controversial issue among the paleoanthropologists. This is because scientists also remain divided among themselves about the issue surrounding the relationship between the two species, the ''birds and the dinosaurs'' (Willis, 1997). Some of the scientists believe that birds have descended from the dinosaurs. In other words dinosaurs are thought to be the ancestors of the birds. Scientists made their assumptions based upon the relationship between the birds and the dinosaurs by studying the fossil remains.

Some scientists based their argument in the fact that the resemblance which exists between the ''fossils of the birds and the dinosaurs suggest the closely relationship'' (Wikipedia contributors, 2006). They were arguing on the basis of the similarities without considering the dissimilarities between the fossils of the two species. For example, birds do not have the same number of the toes, some have three while others have five and more, depending on the continent in which the species are found. In the other cases, some of the bones found in the toes of the birds resemble that of the reptile. Therefore, the question remains, can we say that reptiles are the ancestors of birds?

Scientists further argue that there is no relationship between the birds and the dinosaurs. This time they based their argument in the fact that the ribcage in the fossils of the dinosaurs are compressed from side to side, where on the other side the ribcage in the fossils of the birds are compressed more from back to their belly. By citing the above mentioned differences in ribcage, some scientists believe that the differences between species do not matter most, what matter most is their similarities. The bones in the wing of the bird has been also compared with the bones of the front feet of the dinosaur and the results which have been found indicated that the bones in the wing of the bird and the bones in the front feet of the dinosaur are similar to the bones of any species.

The ''fossils of the birds were also compared with the fossils of the reptiles than that of the dinosaurs'' (Willis, 1997). This is because it has been found that birds and reptiles have many features that they share which are also common in both the species. Characteristics such as long bones; wingless or wings with four functional fingers; long, slender, vertebrated tail; slender, recurved teeth, set in socket and vertebrae biconcave are also found in both the birds and the reptiles. The above mentioned characteristics are different from those which are found in the dinosaurs, such as very hollow bones, fore legs very short, feeble and not used in locomotion.

In conclusion one can also say that the relationship which is thought to have being existed between the birds and the dinosaurs is still unknown. In other words the missing link which is the information confirming the relationship between the birds and dinosaurs is still not known. This is because scientists believe in the process of evolution in order to find the link which can show us that dinosaurs are the ancestors of the birds. The process of evolution is still on, which means that new evidence may be found which will add to the evidence which is already available.

References:

Wikipedia contributors. Dinosaurs [Internet]. Wikipedia, The Free Encyclopaedia; 2006 May 09, 18: 48 UTC [cited 2006 May 10, 15: 12]. Available from: http://en.wikipedia.org/wiki/Dinosaurs

Wikipedia contributors. Birds [Internet]. Wikipedia, The Free Encyclopaedia; 2006 May 08, 22: 58 UTC [cited 2006 May 10, 15: 28]. Available from: http://en.wikipedia.org/wiki/Birds

Willis, P. 1997. Working out relationships. [Online]. Available from: http://www.txtwriter.com/onscience/Articles/dinoblood.html


Peter Muvhali
CSIR PTA
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Tell no 012 8142133
Fax 012 8423676
E-mail smuvhali@csir.co.za
URL: http://blogsoccer-peter.blogspot.com/

THE ADAPTATIONS REQUIRED TO MAKE THE TRANSITION FROM AQUATIC TO TERRESTRIAL LIFE USING AMPHIBIAN AS EXAMPLE

The amphibians (example frogs) were "the first vertebrates that managed a footing on land" (1). Amphibians mean two lives, meaning that they can live in both water and land. They consist of a large group of different animals and frogs are the most familiar groups found in this class vertebrate. "Amphibians are particularly interesting because they are an example of the vertebrate body plan in transition between the aquatic and terrestrial environment" (2).

The transition from an aquatic life to terrestrial one, required modifications of several important body systems, to solve the problems of support and locomotion, gas exchange, desiccation, reproduction, feeding, and the function of some sensory systems. They adapted the different physical properties of water and air temperatures differences between water and land. They had to adapt with the drying out in the terrestrial ecosystem and had to change ways of giving birth. Transformation they had to change the way their circulatory system. When it comes to feeding, most amphibians feed well while they are in the aquatic environment. For example, crocodiles are very strong when they are inside the water when it comes to catching their pray.

The skeleton support was achieved by modification of the pelvic and pectoral fins and by strengthening the vertebral column. The skeletal support for the pectoral and pelvic fins was enlarged and strengthened, and the pelvic girdle became firmly attached to the vertebral column. The lower portions of the limbs were also greatly enlarged to provide an attachment area for powerful muscles. The vertebral column was strengthened by the development of interlocking processes and additional musculature.

The amphibians had to change their ways of locomotion for example in most fish, "the propulsive thrust is provided by the tail and caudal fin which push against the dense water that cause the fish to move forward" (2). In land the paired limbs with their strengthened girdles provided support for the body and also functioned in locomotion. When it comes to reproduction, amphibians had to adapt new ways of reproduction because reproduction in most frogs dependent on water as both fertilization and development. They adapted the way of excretion because most of these amphibians relied on large amount of water to wash away ammonia as excretory product. Therefore they had to use urea as their excretory product and it requires less water.

Although the amphibians managed to solve some changes, they were unable to solve one problem, reproduction in the terrestrial environment. . The problem is that the sperm, egg or developing embryo must be protected from desiccation. Amphibians must return to the aquatic environment to lay their eggs, and fertilize them, and it is there that the developing embryo grows until it is ready to move back up on land. Their adaptation from the aquatic environment to the land revealed a fantastic design that served them well in both environments.

References:

1. Four feet on the ground, [internet] [cited 2006 may 9] Available from:
http://oscar.ctc.edu/access/geology100/life3.html#anchor583986

2. The move to land, [internet] [cited 2006 May 9] Available from: http://instruct1.cit.cornell.edu/Courses/biog105/labs/deuts/movetoland.html

Mr Lufuno Mukwevho
CSIR Pretoria
P.O. Box 395
Pretoria
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Tel: (012) 841 2133
Fax: 012 842 7024.
cell: 0723175626
E-mail: lmukwevho@csir.co.za
Blog url: http://mukwevholufuno.blogspot.com/

REVIEW OF THE EVIDENCE THAT WE HAVE THAT DINOSAURS WERE WARM-BLOODED ANIMALS

Dinosaurs were vertebrates animals, which means that they were animal with backbone. Even today whether dinosaurs were cold-blooded or warm-blooded animals remains unclear. This is because fossil evidence which have been studied by paleoanthropologists prior 1970s indicates that dinosaurs were cold-blooded animals (Wikipedia contributors, 2006). Therefore post 1970s paleoanthropologists have started to find evidence from the fossil remains which indicates that dinosaurs were warm-blooded animals. Being warm-blooded animals mean that dinosaurs were able to control their body temperatures.

Paleoanthropologists did provide evidence which support that dinosaurs were warm-blooded animals. The evidence which were provided by the paleoanthropologists to support their agreement include ''big ribcage, straight legs, rate of evolution, bone structure and the rate of growth'' (Bakker, 1972). All of the above mentioned characteristics support the evidence by the scientists that dinosaurs were warm-blooded animals because of the similar characteristics which are both have in common with birds. The characteristics of the fossil remains of both dinosaurs and birds were compared.

In 1993 the evidence from the fossil remains which have been found in South Dakota, USA prompted paleoanthropologists to believe that dinosaurs were warm-blooded animals. The above statement made by the paleoanthropologists is supported by the fact that dinosaurs were active organisms which were moving at the highest speed. This is because warm-blooded animals are able to control their own body temperature, they donot rely in the external environment. Some paleoanthropologists on the other side disputed the fact that dinosaurs were warm-blooded animals, because in the location where many fossils have been found it was extremely hot. The hot temperature was supposed to kill the dinosaurs.

Bakker (1972) says that in April 2000 a team of paleoanthropologists from the University of North Carolina State led by Michael Hammer said that they have discovered the first fossil of dinosaurs. The fossil was thought to be the fossilized heart. The fossilized heart was named Willo. It was the fossilzed heart which suggests that the fossilized heart resembles that which are found in the warm-blooded animals or bird not reptile. The weight of the fossilized heart was 666 pounds and it was dated to 6mya.

Other group of paleoanthropologists also supported the fact that dinosaurs were warm-blooded animals. Their arguments were based on the study conducted by studying the isotopes in the bones of the dinosaurs. Evidence from the isotopes studied from the bones also suggested that warm-blooded animals grow quickly as compared to the cold-blooded animals which grow slowly. Even though the evidence provided by studying the ''isotopes seemed to be clear that dinosaurs were warm-blooded animals'', but some paleoanthropologists disputes this fact (Bakker, 1972).

In conclusion, one can say that the fact that dinosaurs were either warm-blooded or cold-blooded animals remains unclear. This is because evidence from the study of the fossil remains are still even today providing us with the new evidence of whether dinosaurs are either warm-blooded or cold-blooded animals. The finding of the new evidence come-up with the new information about the reality of this extinct species, dinosaurs. In other words new evidence means new speculation about whether dinosaurs were warm-blooded or cold-blooded animals.

References:

Bakker, R. 1972. Were Dinnosaurs warm-blooded?. [Online]. Available from:
http://www.dinoruss.com/de_4/5c51d90.htm [12 February 1972, 13: 33]

Wikipedia contributors. Warm-blooded [Internet]. Wikipedia, The Free Encyclopaedia; 2006 May 09, 17:28 UTC [cited 10 May 2006, 14:19]. Available from: http://en.wikipedia.org/wiki/Warm_blooded

Williston, S. W. 2005. Are birds derived from dinosaurs? Kansas City Review of Science and Industry 3:224-226. [Online]. Available from: http://www.txtwriter.com/conscience/Articles/dinoblood.html

Peter Muvhali
CSIR PTA
0001
Tell no 012 8142133
Fax 012 8423676
E-mail smuvhali@csir.co.za
URL: http://blogsoccer-peter.blogspot.com/

THE CARTILAGIOUS AND BONY FISH HAVE DIFFERENT MORPHOLOGIES.

The bony fishes are the fish of the large class Osteichthyes. They are differentiated by a skeleton of a bone. They comprise the majority of the modern fish. They are the most plentiful, varied and multifaceted group of fishes. They are more than other fishes by the ratio of 20 is to 1. They include more species compared to all other combined vertebrates. They are characterised by a bony carcass and slippery, scales that cover their bodies (Frank et al, 1995).


The first bony fishes found had the streamlined bodies. Their fins were well developed. They were characterised by the large eyes and mouths. Their characteristics helped them in evasion. The food they collected helped them to thrive in lakes, streams and the sea. They also developed specific adaptations to unique environments. The oldest bony fishes had thick enamel scales, which in the later forms became lighter. The fins are supported by many slender ray-like bones (Frank et al, 1995).

The early forms were substituted in Mesozoic times by the surviving holeosts that include the garpike and bow fish. The rest of holeosts were replaced in the period of the cretaceous. They were replaced by the teleost ray fins. This group of fish include all almost all the living fish. The choanichthyes include the lung fish. The fins seem to be supported by a strong bony axis. The nostrils open into the mouth (Frank et al, 1995).

The (Chonndrichthyes) cartilaginous are the fish that have only cartilage as hard connection tissue. The cartilage is a type of impenetrable connective tissue. It is composed of fibres. Those fibres consist of collagen and elastic fibres. They also consist of matrix and cells called chondrocytes. The chondrocytes are dispersed in the matrix. They are the only cells available in cartilage. Their functions are to generate and maintain the matrix of the cartilaginous (1).

The cartilage is found in the joints, rib cage, and the ear, the nose, in the throat and between invertebral disks. The function of the cartilages is to provide framework to the beginning of the bone deposition. It seems as if the cartilage has three types namely, hyaline, elastic and fibrocartilage. The hyaline type of cartilage can be found lining bones, especially in the joints and inside the bones. The hyaline found to be the centre for the growth of the bone (1).

The bones of animals are collectively known as the skeleton. The bones and the cartilage seem to have derived from the mesoderm. They are having different composition. The cartilage was found to have formed by the condensed mesenchyme tissue. This tissue differentiates the cartilage into chondrocytes. This further secretes the materials that formed the matrix (2).

It seems as if they were two different types of growth that took place in cartilage, namely the appositional and the interstitial. The appositional found to have increased the diameter of the cartilage. The interstitial found to have increases the mass of the cartilage and occur within (3).

The cartilaginous fish do not have the true bone, while the bony fish have the true bone.
References:


[1].The wikipedia contributors, Coordinated Universal Time [Internet], Wikipedia, The Free Encyclopedia; 2006 May 08, 15; 00 UTC [cited May 2006]. Available from: http//en.wikipedia.org/wiki/Cartilaginous.

[2].The wikipedia contributors, Coordinated Universal Time [Internet], Wikipedia, The Free Encyclopedia; 2006 May 08, 15; 30 UTC [cited May 2006]. Available from:
http://en.wikipedia.org/wiki/Bone.

3. Frank H.T, Herbert S, Paul R. (1965) Fossils, a guide to prehistoric life. Page 136 – 137.

Ms Evelyn Maleka

CILLA CSIR

P.O. Box 395

Pretoria,

0001

Tel: (012) 841 2133

Fax: 012 842 7024.

Email:emaleka@csir.co.za

http://malekaevelyn.blogspot.com/

MORPHOLOGICAL DIFFERENCES BETWEEN CARTILAGINOUS AND BONY FISH

Bone fishes also referred to as Osteichthyes-osseous tissue is a hard endoskeletal (internal support structure of an animal) connective tissue. Bones give the body posture structures support and also help in facilitating movement (1). Bony fishes are characterised by a “relatively stable pattern of cranial bones and rooted teeth” (4). The head and pectoral girdles are covered with large dermal bones and the eyeball is surrounded by a sclerotic ring of four small bones. They also have an “operculum, which helps them to breathe without having to swim" (4).

Cartilage is dense connective tissue and “it is composed of cells called chondrocytes. Chondrocytes are “dispersed in a gel-like ground substance called matrix" (2). Cartilage is a vascular (contains no blood vessels) and nutrients which are diffused through the matrix. Cartilage is mostly found “in the joints, the ear, nose, rib cage and in the throat” (2). Cartilages provide a framework for fish which do not have bones and in bony fishes the framework is provided by the bones (2). The cartilaginous fishes are also referred to as Chondrichthyes “which have jaws with paired fins, paired nostrils, scales, two-chambered hearts and a skeleton made of cartilage” (3). Cartilaginous fishes have a tough skin which is covered with dermal teeth also called placoid scales or dermal denticles which protect the fish since it does not have bones (3).

Cartilaginous fishes do not have any bone marrow since bone marrow it is manufacture in the bones so the red blood cells are produced in the spleen and special tissue around the gonads. In the bony fishes the red blood cells are produced in the bone marrow like in humans since they have bones. Cartilaginous fishes have also an “organ where red blood cells are produced called Organ of Leydig. Another unique organ is named epigonal organ, which plays an important role in regulating the immune system" (3).

The brain of cartilaginous fishes is relative to the brain of mammals in weight, and is about ten times the brain of bony fishes. The bony fishes have a relative brain size to be compared with the brain size of humans. One of the explanations why cartilaginous fishes have such large brains is because they are using much less energy and their bodies’ consists mostly of bones. The density of nerve cells in cartilaginous fishes “are much lower than in the brain of bony fishes, making it less energy demanding and allows it to be bigger"(3).

Bony fishes have various types of calcified tissues: dentine, enamel (or enameloids) and bones. Endochondral bone of the bony fishes begins as a cartilage then it later turns to a bone (4). Cartilaginous fish gets calcium from a cartilage called hyaline (3).

Bony fishes get most of their calcium from the bones but the cartilaginous fishes get their calcium from hyaline articular cartilage. Basically bony fishes consist mostly of a cartilage when the fish is still young the bone only develops when the fish starts to grow so even the bony fish use cartilage because cartilage is much more flexible than bones. Cartilaginous fishes are lighter in weight than the bony fishes which are much heavier for example Marlin (5) which weighs up to 820 kg. Bones have a lot of weight than the cartilage so bony fishes will be a little bit lazy since they weigh too much. Cartilaginous fishes are more flexible than bony fishes since their bodies consist mostly of bones and bones are very hard (not even flexible).


References:

1. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 7, 20:02 UTC [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Bone
2. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 21:28 UTC [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Cartilaginous
3. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 5, 20:22 UTC [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Cartilaginous_fish
4. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 7, 12:50 UTC [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Bony_fish
5. Wikipedia contributors. Council of Science Editors [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 15, 09:47 UTC [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Marlin

Lethabo Mosomane
CSIR
Pretoria
0001
Tel: 27 12 841 2133
Fax: 27 12 842 3676
Mail: lmosomane@csir.co.za
http://lmosomane.blogspot.com/

THE STRUCTURE AND SIGNIFICANCE OF DNA TO OUR LIVES

Deoxyribonucleic acid (DNA) is a nucleic acid (“a complex, high-molecular-weight biochemical macromolecule composed of nucleotide chains that convey genetic information”) (2) that are in the form of a double helix. It is able to replicate itself due to its double helix structure. “DNA contains genetic instructions that specify the biological development of all cellular forms of life. DNA is a long polymer of nucleotides and it encodes the sequence of the amino acid residues in proteins using the genetic code mostly a triplets code of nucleotides” (1).

"The DNA molecule is a chemically linked chain of nucleotides. Each DNA molecule consists of sugar (deoxyribose-it has five Carbons and three Oxygen), a phosphate and one of five kinds of nucleobases (bases). DNA strands are composed of nucleotide subunits called polymers.” DNA has five kinds of nucleotides which are commonly referred to by the identity of their bases (1). The bases are adenine (A), thymine (T), uracil (U), cytosine (C) and guanine (G). Uracil (U) is found in the DNA when cytosine (C) is chemically degraded”.

DNA is sometimes referred to as a heredity molecule because it carries genetic propagation (when more DNA is produced from the original strand) of most inherited traits.” DNA can be transferred after been replicated from the parent to the offspring during reproduction. Each and everyone of us has DNA; we have inherited our genomes from our parents. A genome of an organism carries the whole hereditary information of an individual that is encoded in the DNA” (4). Each individual inherits 23 chromosomes from each parent including the X-chromosome (mitochondrial DNA that we inherit from our mothers and Y-chromosome from our fathers (1).

The way in which the DNA strands stay associated is determined by complementary pairing. Each base forms hydrogen bonds A bonds with T and G with C. the hydrogen bonds between A to T is a double bond and between G to C is a triple bond.

Since DNA is a double stranded helix it can also unfold into two single strands by the process called DNA replication. “The two resulting double strands which are identical, each synthesize a new strand by the process called semiconservative replication (the method in which DNA is replicated in all known cells) (5). The DNA molecule is always double stranded when it unfolds another strand is synthesized unless the DNA is mutated (change in genetic material)”.

"DNA contains the genetic information that is inherited by the offspring and this information is determined by the sequence of the base pairs. A DNA strand contains genes and areas where gene regulation takes place. Genes can be viewed as a cookbook or blueprint” (3).

The significance of DNA to us as human beings is that we are able to trace back our ancestors for example scientists used DNA in order to try to find the missing link between “Apes to Man”. Scientists used DNA in order to trace African Eve eight daughters so DNA is so important. DNA contains genes that parents pass on to their children so the generations can be traced back to our ancestors.

Reference:

1. Wikipedia contributors. DNA [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 01, 23:16. UTC [cited 2006 May 3]. Available from: http://en.wikipedia.org/wiki/DNA

2. Wikipedia contributors. Nucleic acid [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 01, 12:48. UTC [cited 2006 May 3]. Available from: http://en.wikipedia.org/wiki/Nucleic_acid

3. Wikipedia contributors. DNA replication [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 2, 04:25 UTC [cited 2006 May 3]. Available from: http://en.wikipedia.org/wiki/DNA_replication

4. Wikipedia contributors. Genomes [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 04:39 UTC [cited 2006 May 3]. Available from: http://en.wikipedia.org/wiki/Genomes

5. Wikipedia contributors. Semiconservative replication [Internet]. Wikipedia, The Free Encyclopedia; 2006 Feb 3, 04:39 UTC [cited 2006 May 3]. Available from: http://en.wikipedia.org/wiki/Semiconservative_replication

Lethabo Mosomane

CSIR

Pretoria

0001

Tel: 27 12 841 2133

Fax: 27 12 842 3676

mail: lmosomane@csir.co.za

http://lmosomane.blogspot.com/

THE MORPHOLOGICAL DIFFERENCES THAT EXIST BETWEEN THE CARTILAGINOUS AND BONY FISH

Fishes are marine vertebrate animals with back bones, dwelling in ocean, sea and in rivers. They are found under the rocks, in sand and mud. Fishes are divided in to three different classes such as Chondrichthyes, Osteichthyes and Agnatha classes. Agnatha fishes are the small animals that have a mouth like a hole in the head that have no movable parts. These fishes do not have paired fins and they have large gills which serve food filters and respiratory organ.


Chondrichthyes fishes have "strong jaws and also have pairs fins, nostrils, scales, two chambered heart and skeletons made by the cartilage. Their mouth located underside of the head and they use their nose to sense where their food is and same of them use electrosensory system because they are unable to see their food see their food because their eyes are fond on top of their head"( 1) .


Sharks, rays and chimaeras are fishes falls under the class chondrichthyes. The other name of chondrichthye is cartilaginous fish. Their skeleton bones are cartilage meaning that they do not have true bones. They have five to seven gills slits. "They use gills to breathe and during their breath, water passes through mouth, over their gills and out through their gills slits"(1). Their eyes are found at the top of their head and they can not see food as it enters to their mouth (1).


Sharks fish are the one species known as jawed fishes. They also have spiracle behind their eyes at the top of the head. Shakes are the biggest fish, they have "big mouth and they have brown with yellow or white dots on their back" (1). Sharks have five to seven pairs of gills and chimaeras fish have only one pair of gills. "The ghost shark has an external smooth skin and one also have one pair of the external gills opening" (1). Cartilaginous fish have fins which help them not to go under the ocean because they do not have air bladder (1).


Rays fishes have "enlarged pectoral fins; their tails are thin and it ranges from short to long in length" (1). These fishes use their pectoral fins to swim by waving them and sharks their tails to swim. Rays mouth is facing downwards and they have flattened teeth. These fishes "feed themselves on the species that are found at the bottom of the ocean" (1). They change the way of breathing in order to avoid sucking up the bottom mud.


The other name of Osteichthyes is true bony fish. These fishes live in all types of water. This class is divided into two classes which are "Sarcopterygii and Actinopterygii" (2). Class Osteichthyes include "coelacanths and the lung fishes and Sarcopterygii include gars, sturgeons, bow fish and telelosts" (2). The skeleton of the bony fishes made by bone and most of them have a scales. Most of bony fish species have "two sets of paired fins and some have one set of paired fins and some have no fins at all" (2). The species that falls under the class Osteichthyes are snapper, grouper and gurnard fishes. The difference between the bony fishes and the cartilaginous is that the bony fishes have cartilage skeleton bone and the bony fishes have a true bone.


References:

1. Wikipedia contributors. [Internet]. Wikipedia, the free encyclopaedia, 2006 May 09, 10:15 UTC. [Cited May 09]. Available from:
http://en.wikipedia.org/wiki/Cartilaginous

2. Wikipedia contributors. [Internet].Wikipedia, the free encyclopaedia, 2006 May 09, 11:50 UTC. [Cited May 09]. Available from:
http://en.wikipedia.org.wiki/Bony




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/

ADAPTATIONS REQUIRED TO MAKE THE TRANSITION FROM AN AQUATIC TO TERRESTRIAL LIFE USING AMPHIBIAN GROUP AS AN EXAMPLE AND THEIR LIMITING FACTORS ON LAND

All amphibians belong to the subphylum taxon vertebrate. It is also said that the transition of amphibians from the land into the water is incomplete, this is because amphibians usually in the area of aquatic environments. The reason why the amphibians live in an area which is close to the aquatic environment is that in ''order for the amphibians to get air from the terrestrial environment, they have to adapt first, even though they have lungs and gills'' (Wikipedia contributors, 2006). The transition which usually occurs in amphibians is that of from aquatic to terrestrial environment.


Wikipedia contributors (2006) further says that the evolutionary relationship of the amphibians does re-occur again and again in each generation. The re-occurrence takes place in this way, frogs leave their eggs hanging around the plants in water, the eggs then hatch by themselves in the water and the young eggs develop into the adult and head towards the land. In this way the frog which is adolescent moves into the land. When they reach sexual maturity, the adult frog then goes back into the water.


Fox (2006) also says that amphibians are organisms which are adapted to the wet environment. The wet environments which are necessary for amphibians include both arid and semi-arid environments. The main reason of why the amphibians require water is that, in water is where the eggs are laid and hatched. Therefore without water on the terrestrial environments means that amphibians cannot adapt to the life on the land.


Water is the most important requirement of the amphibians in order to adapt on land, but algae on the other side is also important. This is because after the eggs have been hatched, they remain hanging in those algae. The young tadpoles also get their food in the algae plants. Therefore by doing so they end up forming the symbiotic relationship, which is the living together of two living organisms without harming each other.


Amphibians such as the frogs have failed to adapt fully on land, this is because other reptiles have already developed the ''common early waterproof skin which contains the egg in the shell'' (Fox, 2006). Another reason of failure to adapt on land is that amphibians also failed to adapt on the warm, dry environment which is found on dry land. Early reptiles, animals and other organisms were succeeding in their adaptations on the land. Another which can also plays an important role in the failure of amphibians to adapt on the land is the low biomass on the land because only the minority of the organisms manage to adapt and survive on land. Other factors such as ''population growth, pollution, diseases and land degradation are some of the limiting factors which play a role in the majority of amphibians not to be found on the land as compared to the aquatic environment'' (Fox, 2006).


It is also said that the first organism which evolve from the ancestors of the fish is amphibians. They evolve in the period of the late Devonian between 360-370mya. Even though the amphibians evolve in the above mentioned period, frogs, caecilians and toads are the only three groups which remain of the ancient amphibians. But nowadays amphibians are found everywhere on the earth where there is availability of the water.


References:

Fox, R. 2006. Comparative vertebrate anatomy. [Online]. Available from:
http://www.dinoruss.com/de_4/5c51d90.htm [19 January 2006, 12: 43]

Wikipedia contributors. Amphibian [Internet]. Wikipedia, The Free Encyclopaedia; 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


Peter Muvhali
CSIR PTA
0001
Tell no 012 8142133
Fax 012 8423676
E-mail smuvhali@csir.co.za
URL: http://blogsoccer-peter.blogspot.com/

HOW THE FIRST PLANTS AND ANIMALS EVOLVED AND BECAME DEPENDANT ON EACH OTHER

Mutualism is the living together of two species whereby they both benefit from this way of life. The interaction between plants and insects during the process of co-evolution has been beneficial to both of them. “Co-evolution between interactions started in aquatic environment before they evolved on the land. The first species to evolve was the eukaryote”(4). This was discovered through the process of fossilisation and it was found that the eukaryote is multi-cellular animal. These first animals were called eukaryotic because they contain nucleus(1).

Through the process of photosynthesis some plant species can generate their own food. “Single cell plants and blue or green algae are the species that co-evolved and these are the same species that produced their own food. These plants help the herbivore animals to depend on them for food. Plants also help them with oxygen. This is where animals depend mostly on plants for their survival because they are gaining both food and oxygen”(3). So finally plants were considered producers because they use the sun as their source of energy, carbon dioxide from the animals and water to produce food. This is mostly where the food chain begins.

The production of oxygen by algae helps the animal species to evolve on land. "The most part of the O-zone layer is formed by oxygen which blocks the dangerous ultraviolet rays of the sun. If there is no oxygen supplied the rays make it impossible for animal species to live out of the water. In case of the plant the rays help them in food production"(2)

The relationship between plants and animals is very broad. Beside food and oxygen animals still depend on plants for shelter. Many animals use the trees as their habitat, mostly birds because that is where they also lay their eggs for reproduction. During reproduction plants depend on animals mostly insects like bees to transport pollen grains to the female flowers. This is far better than wind on increasing plant population(3).

References:

1. Wikipedia contributors. Eukaryote [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 22, 12:39 UTC [cited 2006 May 25]. Available from: http://en.wikipedia.org/w/index.php?title=Eukaryote&oldid=54516796.

2. Kazlev.A.M. 2002, Plants, (Land plants) [Internet] 2006 May 08; 14:00 UTC[cited 2006 May 08] Available from:
http://www.palaeos.com/Plants/default.htm

3. Kohler, S. Plants, [Internet] 2006 May 8, 14:30. UTC [cited 2006 May 07]. Available from: http://www.blueplanetbiomes.org/plants.htm

4. Stein Carter, J. 1999 Co-evolution [Internet] 2006 May 08; 14:15; [Cited 2006 May 08] Available From:
http://biology.clc.uc.edu/courses/bio303/coevolution.htm

Dianah Nangammbi
Cilla CSIR
P.O Box 395
Pretoria
0001
Tel: +27 12 841 2133
Cell: +27 73 121 3589
Email: dnangammbi@csir.co.za
My blogger url: http://wwwdianah.blogspot.com/

SIGNALS USED BY INSECTS TO ATTRACT A MATE FOR SEXUAL REPRODUCTION

Insects are the "most dominant species than any other kind of living creature"(2). About "95% of all the animal species on the earth are insects"(1). Million Insects can exist in a single acre of land. Insects are able to occur in large number because they can give a large number of off springs and they need only small amount of food. They can successfully live in most environments on earth for example desert.


Most insects mate and reproduce sexually between male and female. In insects females can still reproduce without male and this is common to the aphids. They may reproduce by laying eggs and in other insects, eggs hatch inside the female. Eggs can be laid in different places. For example locusts lay their eggs in a small hole until they hatched.

However, there are different signals which the insects use to attract a mate for sexual reproduction. Different semiochemicals are used by insects to attract mating partner. These chemicals mediate interaction between organisms. The chemicals are divided into allelochemicals and pheromones depending on the nature of interactions if it was interspecific or intraspecific. Allelochemicals are those chemicals that important to individuals of a species that are different from the source species. Pheromones are released by a certain species with the effect of having the attraction to the same kind of species.

Insects uses different ways to attract mating partner, which includes movement, colour, sound, vision and glands. For example, the female butterflies will develop some form of movement. The males will then chase those that show that behaviour and then the mating will take place. Male flies also form a compact swarms to attract females for mating. These insects also show some characteristics when coming to mating. These can be seen where male a required to have a form of gift or food to please the female. Fighting is another way where males compete for females, showing the survival of the fittest.

The female moths have scent glands on their abdomen which secrete pheromones to attract the male moth. "The smell of these glands is easily detected by the male moth at a distance that can range from four to eleven kilometres"(1). Sometimes the males secrete pheromone just to induce the females so that they mate.

The other interesting way in which insects attract each other for mating is through sound. Other insects that mostly use sound include mosquitoes, crickets, and grasshoppers. Female mosquitoes produce a note Sound which attracts the male mosquitoes. The male mosquitoes are attracted to the note or sound produced by the wing vibration of the wing. Female grasshoppers, crickets and cicadas are attracted by the sound produced by their males.

Some male insects have some special techniques they use to protect their sperms from other males. This includes guarding the female to prevent her from mating with other male. Genital plugging where accessory glands produce chemicals which plug the vagina allowing female to mate only once. Another technique is when the male scoop the sperms of previous males from female system using apparatus.

These special characteristics of insects prove that they are really the dominant in all living organism and they will continue to dominate every part of the earth.


Reference:

1. How do the sexes find each other, [Internet] [cited 2006 may 8] Available: http://bugs.bio.usyd.edu.au/Entomology/InternalAnatomy/reproduction.html

2. Wikipedia contributors. Insects [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 17, 05:19 20:04 [cited 2006 May 8]. Available from:http://en.wikipedia.org/wiki/Insects

Mr Lufuno Mukwevho
CSIR Pretoria
P.O. Box 395
Pretoria
0001
Tel: (012) 841 2133
Fax: 012 842 7024.
cell: 0723175626
E-mail: lmukwevho@csir.co.za
Blog url: http://mukwevholufuno.blogspot.com/