ANIMAL REPRODUCTIVE STRATEGIES THE ULTIMATE GOAL OF EACH SPECIES Lorraine Kuun, July 2011
Dec 15, 2015
Lorraine Kuun, July 2011
To produce the maximum number of surviving offspring ...
while using the least amount of energy.
This is called the reproductive effort.
What is the ultimate goal of each species?
Lorraine Kuun, July 2011
1. External vs Internal fertilisation2. Ovipary, ovovivipary and
vivipary3. Precocial and Altricial
development4. Amniotic egg5. Parental care
REPRODUCTIVE STRATEGIES
Lorraine Kuun, July 2011
Disadvantages of external fertilisation (outside the body):
1. Wasteful; huge loss of energy – many eggs produced, few survive.
2. Fertilisation not certain.3. Environmental conditions
important for hatching of eggs
External vs. Internal fertilisation
Lorraine Kuun, July 2011
Occurs in insects and terrestrial vertebrates i.e. birds, reptiles and mammals.
Marine mammals and some fish e.g. sharks and rays also have internal fertilisation.
Mating and copulation occurs. Male insects and mammals have a penis –
organ to transfer sperm to body of female. Fluid inside female provide medium for
sperm to swim towards egg cell(s).
Internal fertilisation
Lorraine Kuun, July 2011
OVIPARY – eggs are released and develop outside body of female, fertilisation internal or external, egg yolk only nutrition.
OVOVIVIPARY – Internal fertilisation, egg shell soft, eggs hatch inside body, appears to be born alive, egg yolk nutrition, mother for protection.
VIVIPARY – fertilisation internal, no egg shell, nutrition via placenta.
3.OVIPARY, OVOVIVIPARY, VIVIPARY – terms used to describe what happens when future offspring separates from parent
Most fish, amphibians and lower aquatic forms.
Needs large numbers of eggs.
Lorraine Kuun, July 2011
OVIPARY in aquatic conditions
Lorraine Kuun, July 2011
1. Fewer eggs needed – higher survival rate of offspring.
2. Developing embryo much less vulnerable to predators.
3. Developing embryo not subject to environmental changes e.g. temperature.
4. Young born fully developed, can feed and escape predators more easily.
5. Occurs in some invertebrates, fish and reptiles.
OVOVIVIPARY – how is reproduction maximised?
Lorraine Kuun, July 2011
Young puff adder being “born alive” after hatching inside mother; note position of cloaca.
Lorraine Kuun, July 2011
Occurs in placental mammals, some sharks and scorpions
Fertilisation internal, no shell Placenta responsible for nutrition – young
born alive
1. fewer eggs necessary 2. energy available for nourishment and
protection of embryo, as well as parental care
VIVIPARY maximising reproduction
Lorraine Kuun, July 2011
PRECOCIAL1. Young hatch or born
when almost fully developed
2. Open eyes, hair or down
3. Active or mobile4. Not confined to
nests5. Energy goes into
prenatal development
ALTRICIAL6. Born or hatched
when not well-developed
7. Often naked, lacking hair or down
8. Cannot walk or fly9. Confined to nest or
burrow10. Energy goes into
parental care after birth
4. Precocial vs. Altricial development
Lorraine Kuun, July 2011
Ground-nesting birds e.g. Penguins, domestic poultry, ostriches
Large mammals e.g. Elephants, species of antelope, horses etc
Allows young to fend for itself, feed and stay warm
Stay with herd for protection against predators
Learn from older individuals in herds OFFSPRING HAS GOOD CHANCE OF
SURVIVAL
PRECOCIAL ANIMALS
Lorraine Kuun, July 2011
Mice survive in broods, cared for by mother (left);Kittens born weak and totally dependent on mother (below)
Lorraine Kuun, July 2011
Adaptation of later vertebrates; can lay eggs in terrestrial environment.
Amniotic egg has fluid-filled, extra-embryonic membranes that prevents embryo from drying out.
Earlier vertebrates lay eggs in water; need to return to water/live in water to reproduce.
Amniotic egg lessens dependence on water for reproduction.
5. The Amniotic egg
Lorraine Kuun, July 2011
Fertilisation is internal. Extra-embryonic (not part of embryo)
membranes only develop after fertilisation. Membranes are:1. Amnion2. Allantois3. Yolk sac4. Chorion
Major evolutionary development; allowed first reptiles to colonise land!
The Amniotic egg
Lorraine Kuun, July 2011
The fluid-filled amnion surrounds and protects the embryo, especially against dehydration and shock.
Allantois acts as reservoir for nitrogenous waste in birds and reptiles.
Yolk sac holds nutritious food for development of embryo.
Chorion surrounds all other membranes: in birds it allows for gaseous exchange; in mammals it forms the placenta (taking over functions of allantois and yolk sac, amongst others (see human reproduction).
How does the amniotic egg maximise reproduction?
Lorraine Kuun, July 2011
Any pattern of behaviour in which parent spends time or energy to improve the 1survival, 2condition and 3future reproductive success of offspring.
Care can be given at any stage:1. Prenatal – guarding eggs, building nests,
carrying broods, incubating eggs and placental nourishing.
2. Post-natal – providing food, protecting offspring, teaching offspring.
6. Parental care
Lorraine Kuun, July 2011
Little or no parental care means a low reproductive effort.
Reproductive energy put into producing masses of eggs.
High mortality rate amongst eggs as well as young.
Few individuals survive to reproductive age. E.g. Most fish, amphibians, insects, most
reptiles
Little or no parental care
Lorraine Kuun, July 2011
Few eggs or young produced. Low mortality rate amongst eggs or young. High reproductive effort. Reproductive energy goes into parental care
after birth (post-natal). Most offspring survive to reproductive age. E.g. Mammals, birds, some reptiles,
exceptions amongst fish and Arthropods.
When parental care is given