A complete Summary of Reproductive Animal Strategies. These notes include thorough explanations of the 5 reproductive strategies, including definitions, how each strategy maximizes reproduction, and South African examples which will be required to know in the final IEB Life Science exam. These note...
REPRODUCTIVE ANIMAL
STRATEGIES
What is the goal of each species?
To produce the maximum number of surviving offspring while using the least
amount of energy. This is called reproductive effort
Reproductive effort
Asexual reproduction found in lower and microscopic animals requires low reproductive
effort (it is energy efficient) because it involves a single animal
Sexual reproduction happens in all vertebrates and requires high reproductive effort
(high energy input) as it much more complex
Unique reproductive strategies have developed to ensure maximum reproductive
success in different environments.
Reproductive strategies enable species to breed successfully and survive to reproductive
age
Strategy: genetically determined behaviour
Reproductive strategies:
1. Courtship
2. External vs internal fertilisation
3. Ovipary, ovovivipary, and vivipary
4. Amniotic egg
5. Parental care
1. Courtship
Courtship: behaviour and/or signals that are designed to attract animals for mating and
breeding
Simple strategies
Chemical (pheromones)
Visual (Brightly coloured body parts)
Auditory stimuli
These can be used singly or in combination
Examples:
- Females of some insect species (e.g. moths) produce species-specific pheromones
that guide males towards them
- Most frogs have to return to the water for mating and breeding. Once the males
reach the breeding ground they sing (grunt, croak) to attract females. Each species
has its own song.
, - Male birds advertise when they are ready to mate by singing a species-specific song
that attracts the females. Once the meet the male must then impress and stimulate
the female sexually, often by special plumage.
Complex strategies
The more elaborate forms of courtship are unique to each species
The females usually favour males that are:
- Larger
- Have more elaborate physical features
- Display more energy in courtship behaviours than other males
This helps the female to choose the better male, which can reinforce pair bonding
(important for parental care) and promises healthier offspring (more will survive)
Examples
- The Blue Cranes’ courtship displays include a complex
and extended series of calls and elaborate dances by
the males
- Springboks have an annual rut (a period of sexual
excitement). To attract females, males defend
territories with loud grunts, attack vegetation with
their horns and deposit middens of urine and dung in
a ritualised display.
- The male African Hoopoes feed insects to their mates. This allows the female to
save her energy for incubating and brooding.
How will courtship maximise reproduction?
Ensures that males and females find suitable mates, e.g. the strongest male
Sexual behaviour in courtship is timed so that the male and female are ready for mating
at the same time.
Energy expenditure is usually by the male, the female saves her energy for breeding.
2. External vs internal fertilisation
Fertilization: the joining of the nucleus of an egg and sperm
The sperm are motile as they are able to swim but eggs do not move.
Vertebrate species therefore have various ways of ensuring that sperm reach the eggs
for fertilisation to take place.
External fertilization
External fertilisation takes place in water and
occurs in most aquatic animals
E.g. fish and frogs
It is not an ideal process as:
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