By Pizza No.26 & Meen No.12 MEP M.6

2. Origin of species
Species, In biological terms, it is an individual
belonging to a population whose members have
common characteristics as well as the potential to
interbreed with one another to produce viable
offspring, but who cannot successfully interbreed
with members of other species.

3. Reproductive Barriers Separate Species
Each species is genetically isolated by other such
population by reproductive barriers
Any factor that prevent two species from
producing viable, fertile hybrids is a reproductive
barriers that maintains the integrity of a species.
There are prezygotic and postzygotic barriers

4. Reproductive Barriers
Separate Species
Prezygotic
Barriers
Habitat
Isolation
Behavioural
Isolation
Temporal
Isolation
Postzygotic
Barriers
Reduced Hybrid
Viability
Reduced
Hybrid fertility
Hybrid
Breakdown

5. Prezygotic Barriers
Habitat Isolation is where sepecies occupying
the same geographic area live in separate habitats.
Habitat Isolation can be a result of habitat
destruction by human activities. The endangered
damselfy Coenagrion mercuriale is the key
component of the European freshwater ecosystem.

6. Prezygotic Barriers
• Behavioural Isolation
sepecies that process unique, exclusive mating
signals and display certain courtship rituals are
separated by what is known as Behavioural Isolation
Example of Behavioural Isolation
is the courtship rituals performed
by blue-footed boobies. Part of
the rituals calls for male to
‘high-step’, displaying the blue
feet that is characteristic of
the species

7. Prezygotic Barriers
Temporal Isolation
Two sepecies that breed at different times of the
day, different seasons or different years are
separate by temporal isolation
Example is the periodical
cicada Magicicada
septendecim, which spends
most of its life in several
juvenile stages underground.

8. Postzygotic Barriers
• Reduced Hybrid Viability
After the formation of a zygote, genetic
incompatibility between two species may abort the
development of the hybrid at some embryonic
stage,or produce frail offspring in cases where
hybrid development is complete.
Example, frog genus Rana, of which several
species live in the same regions and habitats and
occasionally hybridise

9. Postzygotic Barriers
• Hybrid Breakdown
In cases where mating takes place across
species, the hybrid survives but with very low
fitness. This prevents gene flow between species.
Example of this can be seen in cotton plant

10. Postzygotic Barriers
• Reduced Hybrid fertility
Even when the hybrid of two species
successfully mate and produce vigorous offspring,
reduced hybrid fertility or hybrid sterility occurs
where by the hybrid offspring are completely or
largely sterile.
Example, the mule is
a robust but sterile
hybrid between a horse
and a donkey