Transcript Animal Reproductive Strategies Part B

3.OVIPARY, OVOVIVIPARY, VIVIPARY –
terms used to describe what happens
when future offspring separates from
parent
• 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.
Lorraine Kuun, July 2011
OVIPARY in aquatic conditions
• 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.
Lorraine Kuun, July 2011
OVIPARY in terrestrial (land)
environments – maximising
reproduction
• 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.
Lorraine Kuun, July 2011
Hard shell good protection for developing embryo;
prevents embryo from drying out.
Lorraine Kuun, July 2011
Shark egg pouch with yolk clearly visible
Lorraine Kuun, July 2011
OVOVIVIPARY – how is reproduction
maximised?
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.
Lorraine Kuun, July 2011
Dogfish embryo with yolk sac
Lorraine Kuun, July 2011
Lorraine Kuun, July 2011
Young puff adder being “born alive”
after hatching inside mother; note position of cloaca.
Lorraine Kuun, July 2011
VIVIPARY
maximising reproduction
• 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
Lorraine Kuun, July 2011
Lorraine Kuun, July 2011
4. Precocial vs. Altricial development
PRECOCIAL
1. Young hatch or born
when almost fully
developed
2. Open eyes, hair or
down
3. Active or mobile
4. Not confined to nests
5. Energy goes into
prenatal development
ALTRICIAL
1. Born or hatched when
not well-developed
2. Often naked, lacking
hair or down
3. Cannot walk or fly
4. Confined to nest or
burrow
5. Energy goes into
parental care after
birth
Lorraine Kuun, July 2011
PRECOCIAL ANIMALS
• 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
Lorraine Kuun, July 2011
Left: Penguin chick and
Above: foal, both mobile
soon after birth
Lorraine Kuun, July 2011
ALTRICIAL ANIMALS
• 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
Lorraine Kuun, July 2011
Altricial bird – see mouth-lining that attracts mother
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
5. The Amniotic egg
• 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.
Lorraine Kuun, July 2011
The Amniotic egg
• Fertilisation is internal.
• Extra-embryonic (not part of embryo) membranes only
develop after fertilisation.
• Membranes are:
1. Amnion
2. Allantois
3. Yolk sac
4. Chorion
Major evolutionary development; allowed first reptiles
to colonise land!
Lorraine Kuun, July 2011
The Amniotic egg
Lorraine Kuun, July 2011
How does the amniotic egg maximise
reproduction?
• 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).
Lorraine Kuun, July 2011
Amniotic egg as seen in human
embryonic development
Lorraine Kuun, July 2011
6. Parental care
• 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.
Lorraine Kuun, July 2011
Little or no 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
Lorraine Kuun, July 2011
When parental care is given
•
•
•
•
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.
Lorraine Kuun, July 2011
Right: chicken
laying egg,
mother feeding
young
Left: Midwife toad
Ovovivipary type
of parental care
Left: Male seahorse with
young emerging
from breeding pouch
Lorraine Kuun, July 2011
Lorraine Kuun, July 2011