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Part VI : Animal Reproduction

Mating on Land Homepage
Mating and Fertilization Summary (useful for revision)
Mating and Fertilization : Questions

Introduction to Animal Reproduction
Reproduction in Birds
Inside the bird's egg.
How birds take care of their chicks
Reproduction in Mammals
Gestation and Birth
Care of the new-born Offspring
Different Ways of Growing

Topic Chapters Index

 

Raft Spider © Paul Billiet

Mating can be a dangerous business
for a male spider

 

Moth antennae © Shirley Burchill

Female moths send a strong perfume into the air

 

A mating pair of Adélie penguins greeting each other, Antarctica © Shirley Burchill

Some penguins have difficulty in recognizing each other and in distinguishing males from females

 

A bull, Yorkshire, UK © Shirley Burchill

Many cows are fertilized by artificial insemination

 

Artificial Insemination

Trout are bred in trout farms. The female fish are taken and squeezed to that their eggs are released into a special container. A 500 g female trout will provide between 500 and 1 000 eggs. The male is then held and squeezed so that his sperms are released into the same container which contains the eggs. The eggs and sperms are then mixed and left for ten minutes to ensure fertilization. The fertilized eggs are then incubated in a long tray of water.

Many cows are fertilized by artificial insemination. The sperms are collected from a bull and stored at a temperature of - 186°C. The sperms can then be sold for use when they are required. A bull usually produces 6 cm3 of semen, containing the sperms with each ejaculation. The semen contains 9 billion sperms (1 billion = 1000000000). When this liquid is separated into smaller volumes there is enough to fertilize 250 cows.

 

MATING AND FERTILIZATION II

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Scorpions

To avoid being stung or injured the male scorpion has to quickly hold the female's pincers with his own during mating. The two scorpions then "dance" backwards and forwards, which has the effect of clearing an area on the ground. The male then places a packet of sperm cells from underneath his thorax onto the cleared ground. Then he has to pull and push the female until the sexual pouch underneath her thorax is above the packet of sperm.

When the eggs hatch inside the pouch, the young scorpions crawl out and onto their mother's back. They stay on her back for fourteen days.

 

Spiders

Mating can be a dangerous business for a male spider. He prepares himself before he meets a female. He spins a triangle of silk a few millimetres long and puts a drop of sperms from a gland underneath this body onto the silk triangle. This packet of sperms is then sucked into a hollow pouch in a special leg called the pedipalp.

The male signals with his front legs to attract the female. His pedipalp is often brightly coloured to catch her attention. It is important that the female recognizes the male or she will attack him as she would any prey. The male carefully approaches the female and positions himself to squirt the packet of sperms from his pedipalp into her sexual opening. Once this has been achieved he has to escape very quickly. If he is not quick enough the female will eat him.

 

Crickets and Cicadas

Crickets and cicadas use sounds to attract the opposite sex. Other insects, such as the firefly, use light signals. The male firefly risks his life by flying through the air on warm summer nights, signalling to females with his flashing light. The females return their signals from the safety of the vegetation. Different species of fireflies are thought to have different codes of flashing lights.

 

Moths

Female moths send a strong perfume into the air. The male emperor moth is able to detect the perfume of a female at a distance of 11 km when the wind is blowing the perfume towards him. The male moths use their antennae to detect the female's perfume. A female emperor moth releases only 0,0001 mg of perfume into the night air.

 

Penguins

Most penguins have difficulty in recognizing each other and in distinguishing males from females. They are not able to dance or sing to attract a male, (although they do make a lot of noise!).

 

A male Adélie penguin offers a stone to, what he hopes, is a female, Antarctica © Shirley Burchill

 

The male penguin makes his intentions known to another penguin by offering it a pebble. This is done to suggest building a nest. If the pebble is rejected, the other penguin was either an unready female or another male!

 

Twins

A fertilized sea urchin egg cell undergoes its first division © Paul Billiet

 

Amongst humans, giving birth to two or more babies at once is not common, so we regard twins as rare but in the animal world it is quite common. This type of twin, from the fertilization of two eggs by separate sperms, is called a fraternal twin because the babies are all brothers or sisters of one another. There is another type of twin called an identical twin. This is quite different and to understand it we need to know what happens to the egg after fertilization.

After the sperm cell fuses with the egg cell no more sperm cells can enter the egg cell. After a few hours the fertilized egg cell divides into two, then into four, then into eight and so on until a ball of cells develops. This is the beginning of the embryo. If at this stage the ball of cells breaks in two - which can happen - two separate babies can form and they will be identical to one another.

In conjoined twins the ball of cells does not completely separate and the babies are born attached to each other. If the attachment between the twins is not too great they can be separated. They are often called Siamese twins because the first pair of this type of twin to be described in 1820 came from Siam, which is called Thailand today. This does not mean that there are a lot of twins joined together in Thailand. There are no more there than anywhere else. Conjoined twins are very rare amongst humans and other animals.

 

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