1. Speciation and Evolution

2. MICROEVOLUTION
Changes in allele frequencies and phenotypic traits within a population and species
But what factors leads to SPECIATION?

3. SPECIATION The formation of a new species
SPECIES: all the members of a population that can interbreed under natural conditions
The offspring must also be able to reproduce
Individuals of different species CANNOT interbreed under natural conditions and are described as being REPRODUCTIVELY ISOLATED

4. MODES OF SPECIATION There are three modes of speciation:
REPRODUCTIVE ISOLATION MECHANISMS
ALLOPATRIC SPECIATION
SYMPATRIC SPECIATION

5. SPECIES FORMATION
REPRODUCTIVE ISOLATION MECHANISM: any behavioural, structural or biochemical trait that prevents individuals of different species from reproducing successfully together
There are two kinds of mechanisms:
PREZYGOTIC
POSTZYGOTIC

6. PREZYGOTIC MECHANISM
A reproductive isolating mechanism that prevents interspecies mating and fertilization
EXAMPLES:
Ecological Isolation
Temporal Isolation
Behavioural Isolation
Mechanical Isolation
Gametic Isolation

7. BEHAVIOURAL ISOLATION
Different species use different courtship and other mating cues to find and attract a mate
EXAMPLE: Male frogs of different species have unique calls that attract only females of their own species

8. TEMPORAL ISOLATION
Different species breed at different times of the year.
EXAMPLE: Pussy willows produce flowers in the early spring, while other species produce flowers at different times

9. ECOLOGICAL ISOLATION
Very similar species may occupy different habitats within a region
EXAMPLE: The mountain bluebird lives at high elevation while the eastern bluebird prefers low elevation

10. MECHANICAL ISOLATION
Differences in morphological features may make two species incompatible
EXAMPLE: The male and female genitalia of each species of damselflies are physically incompatible

11. GAMETIC ISOLATION
Male gametes may not be able to recognize and fertilize an egg of a different species
EXAMPLE: Sea cucumbers release their sperm and eggs into open water. The sperm recognize their own species through chemical markers

12. POSTZYGOTIC MECHANISM
A reproductive isolating mechanism that prevents maturation and reproduction in offspring from interspecies reproduction
EXAMPLES:
Zygotic Mortality
Hybrid Inviability
Hybrid Infertility

13. ZYGOTIC MORTALITY
Mating and fertilization are possible but genetic differences result in a zygote that is unable to develop properly
EXAMPLE: Sheep and goats may mate but the zygote is not viable

14. HYBRID INVIABILITY
A hybrid individual develops but either dies before birth or if born alive, cannot survive maturity
EXAMPLE: When tigers and leopards are crossed, the zygote begins to develop but the pregnancy ends in miscarriage or stillborn

15. HYBRID INFERTILITY
Hybrid offspring remain healthy and viable but are sterile
EXAMPLE: Mules are the sterile hybrid offspring of a horse and donkey cross

16. ALLOPATRIC SPECIATION
The formation of a new species as a result of evolutionary changes following a period of geographic isolation
Once populations are physically separated they can no longer exchange genetic information
Over many generations the populations will gradually become less and less alike
When re-introduced, the species cannot interbreed

17. ALLOPATRIC SPECIATION

18. SYMPATRIC SPECIATION
The evolution of populations within the same geographic area into separate species
Such isolation may occur gradually or suddenly
A single mutation can render an individual unable to reproduce with other members of the population
Disruptive selection can cause sympatric speciation thus creating a new species