Transcript 2.4 Reproductive Strategies

2.4 Reproductive Strategies
Key Themes
• 2 Types of reproduction (sexual & asexual)
• Both internal and external fertilisation
• Adaptations to life on land
– Eggs (birds and reptiles)
– Internal gestation (mammals)
– Insects
• Flowering plants
Asexual reproduction
• Individuals are genetically identical (clones)
• Cells with diploid number are produced by
mitosis
• Advantages:
• Disadvantages:
Sexual reproduction
• Produces offspring that are genetically
different
• Haploid cells or gametes are produced by
meiosis
• Advantages:
• Disadvantages:
• Males and females produce different sized
gametes
• Fertilisation involves the fusion of a haploid
sperm and a haploid egg
 diploid zygote
• Most aquatic beasties undergo
External Fertilisation
– will lay eggs (sometimes in a nest)
– then spread sperm over those eggs
Internal fertilisation
• Advantages:
• In many animals the fertilised
egg / zygote actually develops outside of the body
– Examples?
• When this is the case, a large number are
produced to increase survival
Adaptations to life on land
•
•
•
•
Amphibians
Reptiles
Birds
Mammals
All these _____ show increasing adaptations for
colonising the land
Reptiles and Birds
• Evolution of the amniotic egg
• Anatomy of the egg:
– Fluid filled cavity
– Membrane
– Protective shell
– Encloses embryo
inside the yolk sac
• Birds incubate eggs, the embryo completing
development outside the mothers body
Mammals
• Young are retained in uterus / womb without a
shell
• Embryo is nourished there from mother’s blood
supply via a placenta
• Means that young can be born fairly well
advanced in terms of development
discussion point:
Different species have diff strategies on this
Parental care
•
•
•
•
•
What animals exhibit parental care?
What are the advantages?
How many offspring do your examples have?
Name something that has no parental care…
How many offspring does that have?
*As degree of parental care increases, number*
of offspring decreases
Insects
• Abundant, Diverse & Widespread
Insects lives and lifestyles affect almost all other
terrestrial organisms
• Insect zygotes develop into an intermediate form
(nymph or larva) before becoming an adult
Nymphs
Nymphs
resemble the
adults
They go through
several moults
(instar)
Incomplete
metamorphosis
Larvae
Different from
the adult form
Larval stage
followed by
pupa
Then complete
metamorphosis
into the adult
Flowering Pants
• Flowering Plants are well adapted for life on
land in terms of their morphology and
reproduction
• They have similar reproductive strategies to
animals for colonisation.
… what are they?
http://www.videopediaworld.com/video/22961
/11-30-the-private-life-of-plants--03-flowering
Plant relationships
• Key to plant success is their relationship with
animals:
– Pollination
– Seed Dispersal
The Seed
• Food store enables
embryo to develop until
leaves are produced
• Resilient coat allows it
to withstand adverse
conditions