OVIPARY – eggs are released and develop outside body of female, fertilisation internal or external, egg yolk only nutrition. OVOVIVIPARY – 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.• Larval stage self-sufficient; don’t

compete with parents – use different food sources.

• Eggs and larvae easily dispersed.


OVIPARY in aquatic conditions


• Invertebrates produce large numbers of eggs to ensure survival (no or little parental care).

• Protective shell prevents embryo from drying out.• Fewer eggs in e.g. birds and reptiles – energy can be

used for more food in egg (yolk and albumin), hatching and protection, parental care.

• Development of amnion important factor in success.

OVIPARY in terrestrial (land) environments – maximising reproduction


Hard shell good protection for developing embryo; prevents embryo from drying out.


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?


Dogfish embryo with yolk sac



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-developed7. Often naked, lacking

hair or down8. 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


• Small animals that produce big litters e.g. mice, rats, cats, dogs

• Tree-nesting birds that have nests away from predation

• Humans (see human reproduction)• Altricial species need parental care for a long time –

usually female that does the caring, male sometimes involved.

• Birds usually have mouth-lining or gape-edge• Mammals small and immature brains

ALTRICIAL ANIMALS


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?


Amniotic egg as seen in human embryonic development


• 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

Left: Midwife toad

Right: chicken laying egg, mother feeding young


Ovovivipary type of parental care

Left: Male seahorse with young emerging from breeding pouch


Documents

OVIPARY – eggs are released and develop outside body of female, fertilisation internal or external, egg yolk only nutrition. OVOVIVIPARY – Internal fertilisation,