SPECIATION AND EVOLUTION

MICROEVOLUTION Changes in allele

frequencies and phenotypic traits within a population and species

But what factors leads to SPECIATION?

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

MODES OF SPECIATION

There are three modes of speciation:1. REPRODUCTIVE ISOLATION

MECHANISMS

2. ALLOPATRIC SPECIATION

3. SYMPATRIC SPECIATION

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:PREZYGOTICPOSTZYGOTIC

PREZYGOTIC MECHANISM

A reproductive isolating mechanism that prevents interspecies mating and fertilization

EXAMPLES: ○Ecological Isolation○Temporal Isolation○Behavioural Isolation○Mechanical Isolation○Gametic Isolation

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

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

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

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

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

POSTZYGOTIC MECHANISM

A reproductive isolating mechanism that prevents maturation and reproduction in offspring from interspecies reproduction

EXAMPLES:○Zygotic Mortality○Hybrid Inviability○Hybrid Infertility

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

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

HYBRID INFERTILITY

Hybrid offspring remain healthy and viable but are sterile

EXAMPLE: Mules are the sterile hybrid offspring of a horse and donkey cross

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

ALLOPATRIC SPECIATION

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