REPRODUCTIVE STRATEGIES
‘What is courtship behaviour
It is the special behaviour that animals use to attract mating partner when they are ready to
bread.
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E.g Male spiders jumping and dancing before their females displaying their
bright colours
Male peacock making harsh call ,females gather around at the display site
then the male display their large brightly coloured feathers of their tails. Then
females select their partners.
FERTILISATION
It is the fusion of the male and female gametes to form a zygote
Types of fertilisation
a) External fertilisation
- The sperm cells fertilises the egg cell outside the body of the female e.g in fish
sperm cells swims to the egg cells in water.
- To ensure that fertilisation takes place thousands of egg cells are produced to
increase chances of fertilisation and reproduction of species
- Common in aquatic animals such as sponges , jelly fish,frog fish etc
NB: Water is always required for external fertilisation to ensure that eggs do not dry
out and sperm cells are allowed to swim towards eggs
Advantages of external fertilisation
-
Does not need much energy
No need for males to have a special organ to insert the sperm into the female body
No additional energy is needed for parental care or formation of a protective layer
Disadvantages of external fertilisation
-
A large number of sperm cells may not reach the egg cells.( since a large number
is produced to ensure that some sperm cells reach the eggs) / chances are very
slim for sperm cells to meet with egg cells of the same species.
b) Internal fertilisation
- Male deposit sperm cells inside the reproductive organs of the female and
fertilisation occurs inside the female reproductive organs.
- It occurs in mammals that produce a few offspring.
Advantages of internal fertilisation
-
It allows terrestrial animals to reproduce in a dry environment.e.g birds and
mammals / it allows for fertilisation even on dry habitas
Because it is more certain than external fertilisation a small quantity of sperm
cells are produced. / greater chances of fertilisation
METHOD OF EMBRYONIC DEVELOPMENT
1) Ovipary – method of reproduction in which eggs are laid and development of
these eggs take place outside the mothers body .e.g in birds
i.e eggs are fertilised internally before laid or they may be fertilised after being
laid . Each egg eventually hatches into a young animal.
- Many vertebrates ( e.g frogs) reproduce this way.
Disadvantages
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Eggs may be preyed upon by predators.
Mortality is very high
2) Vivipary – method of reproduction in which the young develop inside the uterus
of the mother after then eggs are fertilised internally ( receiving nutrients from the
mothers blood through a placenta. The mother gives birth to the active offspring.)
Mammals e.g humans
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Advantages
Greater chance of offspring being produced because fertilisation is internal /
offspring from vivipary are less prone to predators unlike ovipary
Young ones are already well developed when born
3) Ovovipary - method of reproduction in which the young ones develop from the
eggs that are fertilised internally and retained within the mother body after
fertilisation but obtain nutrients from the egg yolk and not from the mothers
blood.
- The young one hatch inside the mother reproductive system and born soon
afterwards. E.g fish ( shark) and reptiles (some snakes ,lizards)
Advantages of ovoviparity
-
Because of internal fertilisation there is a greater chance of offspring produced
Young one already developed.
Less prone to being eaten by predators compared to the eggs in ovipary
AMNIOTIC EGG
( it is characteristics of birds and reptiles)
-
An egg that has a yolk and three other membranes; the amnion, chorion and
allantois
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Amnion – cushions the embryo against mechanical shock
- Protects the embryo from shock and stops it from sticking to the shell
 Allantois – it stores waste produced by the embryo also functions in gaseous
exchange like chorion
 Chorion – allows oxygen which enters the shell to pass through to the
embryo.
 Yolk sac – it contains yolk which serves as food for the embryo
Chorion- placenta - the connection between mother and developing
embryo. The placenta is an organ through which materials are exchanged
between the mother and the developing embryo.
Amnion- amniotic sac - fluid filled structure that cushions and protects the
developing fetus
Yolk sac– form part of the umbilical cord, provide oxygenand food and
remove waste products 
Allantois- part of the umbilical cord, provide oxygen and food and remove
PRECOCIAL AND ALTRICIAL DEVELOPMENT
Precocial – production of offspring that are independent can feed and move by themselves
the moment they are born or/hatch
OR
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Young one are relatively matured and they are able to move around after they are
born or hatch
Altricial – production of offspring that are born helpless, unable to move or feed by
themselves the moment they are born or / hatch e.g do not have any hair or down feathers and
need to be looked after by adults for quite a long time.
PRECOCIAL
Eyes are open when they hatch
Bodies are covered with soft feathers called
downs
Able to move soon after hatching
Able to feed themselves
Independent of their parents
ALTRICIAL
Eyes closed when they are born
Bodies do not have down feathers
Unable to move about soon after hatching
Unable to feed themselves
Dependent on their parents
Parental care – looking after the young ones through feeding, keeping them warm ,
protecting them from the predators
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This increases chance of survival of the offspring
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Few offspring are produced