the ultimate goal of each species lorraine kuun, july 2011

Lorraine Kuun, July 2011

ANIMAL REPRODUCTIVE

STRATEGIESTHE ULTIMATE GOAL OF EACH SPECIES


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?


1. External vs Internal fertilisation2. Ovipary, ovovivipary and

vivipary3. Precocial and Altricial

development4. Amniotic egg5. Parental care

REPRODUCTIVE STRATEGIES


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


Mating occurs, but no copulation


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


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.


OVIPARY in aquatic conditions


Shark egg pouch with yolk clearly visible


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?


Young puff adder being “born alive” after hatching inside mother; note position of cloaca.


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


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


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


Left: Penguin chick andAbove: foal, both mobile soon after birth


Altricial bird – see mouth-lining that attracts mother


Mice survive in broods, cared for by mother (left);Kittens born weak and totally dependent on mother (below)


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


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


The Amniotic egg


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?


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


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


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

the ultimate goal of each species lorraine kuun, july 2011

Documents

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species lorraine kuun

birth lorraine kuun

parental care lorraine

egg yolk nutrition