Reproductive strategies
Grade 12
REPRODUCTIVE STRATEGIES
IN VERTEBRATES
• Fertilisation occurs when a sperm cell and egg cell fuse to
form a zygote.
• Fertilisation can either occur outside or inside the female’s
body and varies in its water dependency.
Two fertilisation strategies are distinguished:
a) External fertilisation
b) Internal fertilisation
Comparison of external and internal fertilisation
External fertilisation Internal fertilisation
Requires water for fertilisation No water required for fertilisation
Gametes (sperm and egg cells) are Sperm cells are released into the
released into water female’s body
Many gametes released Fewer gametes released
High mortality rates among young Lower mortality rates among young
due to lack of protection. Eggs can – protection provided by the
easily desiccate or be predated on mother’s body or a hardened
calcareous / leathery shell.
e.g. fish and amphibia e.g. reptiles; birds and mammals
Reproductive strategies
• Reproduction strategies indicates where the embryo
develops and how the embryo receives nutrition.
• There are three types of reproductive strategies namely;
a) Ovipary
b) Ovovivipary.
c) Vivipary.
Comparison of ovipary, ovovivipary and
vivipary
Ovipary Ovovivipary Vivipary
Fertilisation External or internal Internal Internal
Development The eggs are laid by the female The egg hatches within the body of A type of reproduction
of embryo and the embryo develops inside the female where the foetus
the egg. develops in the uterus of
the female
Nutrition Yolk is the only form of Yolk present in the egg. Young are Young receive nutrition
nutrition for the developing independent of the mother’s body from the mother’s body
embryo and is usually present in through the placenta
small quantities
Type of egg jelly-like or calcareous calcareous or leathery None
Activity 1: Fertilisation
The diagram below shows a certain species of fish mating.
1. Identify the type of fertilisation displayed by the fish species. (1)
2. State two visible ways in which the chances of fertilisation in these fish are
increased. (2)
3. Name the reproductive strategy used by these fish that involves the
production of eggs. (1)
4. Give two reasons why there is no need for the eggs of these fish to be
covered by a hard or leathery shell. (2)
5. Explain the challenge that external fertilisation poses and how organisms with
external fertilisation overcome this challenge. (4)
(10)
The amniotic egg
• The amniotic egg is a major development in the evolution of animal life on land
from being water dependent for sexual reproduction, to being able to reproduce
without the availability of water.
Precocial and Altricial development
• Precocial and altricial development are terms used to describe how
well-developed offspring are at birth.
• Major differences between precocial and altricial development
Precocial development Altricial development
Development of the body Well-developed Under-developed
Eyes after birth Open closed
Presence of fur / feathers Have fur / feathers usually naked
Parental care required Low degree of parental high degree of parental
care required care required
Mobility Young can move soon Young have limited ability
after birth to move freely
Yolk amount in egg Greater quantity Lower quantity
PARENTAL CARE
• In higher-order animals, parental care is a behaviour that increases
the survival of the young.
• As a reproductive strategy, those animals which invest more energy
before birth usually display very little parental care once young
have been born.
• In animals where less energy is invested pre-natally (before birth),
more post-natal (after birth) parental care is offered.
Parental care can be seen in the following examples:
Building of nests and incubation of eggs
Guarding from predators
Teaching offspring
