SpeciationSpeciation

SpeciationSpecies: A group of organisms capable of

interbreeding= they are isolated reproductively from other

species 1) Live together but cannot interbreed2) Live a distance apart

Isolating MechanismsPrezygotic isolating mechanisms: Barriers that

are in place before fertilization can occur. Eg. A mountain range between two populationsEg 2) Red clawed crab

Isolating MechanismsPrezygotic isolating mechanisms: Barriers that are in

place before fertilization can occur. Eg. A mountain range between two populations

Postzygotic isolating mechanism: Barriers that are in place after fertilization which prevent the production of fertile offspring

Eg. 1) Sperm and egg come together but the sperm is not able to enter the egg

Eg. 2) Offspring are produced but are infertile (mules)

Reproductive Isolating MechanismsPrezygotic Isolations

Definition Example

Habitat Isolation

Two species that live in the same location but in different habitats

One species may live in the trees one on the

forest floor

Reproductive Isolating MechanismsPrezygotic Isolations

Definition Example

Habitat Isolation

Two species that live in the same location but in different habitats

One species may live in the trees one on the

forest floor

Temporal Isolation

Two species have different breeding seasons. Individuals

become fertile at different times.

One flower may produce reproductive structures in

May another in August

Reproductive Isolating MechanismsPrezygotic Isolations

Definition Example

Habitat Isolation

Two species that live in the same location but in different habitats

One species may live in the trees one on the

forest floor

Temporal Isolation

Two species have different breeding seasons. Individuals

become fertile at different times.

One flower may produce reproductive structures in

May another in August

Behavioral Isolation

Animals have specific mating dances, calls and pheromones

A female peacock will only breed with a male who

can put on a good display

Reproductive Isolating MechanismsPrezygotic Isolations

Definition Example

Habitat Isolation

Two species that live in the same location but in different habitats

One species may live in the trees one on the

forest floor

Temporal Isolation

Two species have different breeding seasons. Individuals

become fertile at different times.

One flower may produce reproductive structures in

May another in August

Behavioral Isolation

Animals have specific mating dances, calls and pheromones

A female peacock will only breed with a male who

can put on a good display

Mechanical Isolation

Two species are not capable of mating

Genitalia does not match up

Reproductive Isolating MechanismPostzygotic Definition Example

Gamete Isolation

Sperm can’t get to the egg Sperm is designed for a shorter reproductive tract and cannot

make it

Reproductive Isolating MechanismPostzygotic Definition Example

Gamete Isolation

Sperm can’t get to the egg Sperm is designed for a shorter reproductive tract and cannot

make itZygote

IsolationFertilization occurs but zygote

cannot surviveFetus does not develop properly

and dies

Reproductive Isolating MechanismPostzygotic Definition Example

Gamete Isolation

Sperm can’t get to the egg Sperm is designed for a shorter reproductive tract and cannot

make itZygote

IsolationFertilization occurs but zygote

cannot surviveFetus does not develop properly

and dies

Hybrid Sterility Hybrid survives but cannot produce its own offspring

Two species mate to produce an offspring that is sterile such as a

mule

Reproductive Isolating MechanismPostzygotic Definition Example

Gamete Isolation

Sperm can’t get to the egg Sperm is designed for a shorter reproductive tract and cannot

make itZygote

IsolationFertilization occurs but zygote

cannot surviveFetus does not develop properly

and dies

Hybrid Sterility Hybrid survives but cannot produce its own offspring

Two species mate to produce an offspring that is sterile such as a

mule

F2 Fitness Hybrid can reproduce but their offspring cannot

The offspring of 2 species is able to reproduce but their offspring

can’t

The Process of Speciation

Speciation: When one species divided into two different species. Usually by mutation.

Allopatric Speciation: Geographic barriers such as rivers or mountain ranges divide a population. This prevents gene flow between the populations. Overtime the two populations develop into different species.

Allopatric Speciation

Sympatric Speciation

Sympatric Speciation: A new species is created within a population without the presence of geographical barriers.

Eg.

Sympatric Speciation

Sympatric Speciation: A new species is created within a population without the presence of geographical barriers.

Eg. One organism in a population of plants loses a chromosome. Because the chromosomes do not line up with its own species it can only reproduce with itself. Eventually it creates its own population of interbreeding plants.

Pace of Speciation

2 Hypothesis that address the pace of speciation

1) Phyletic Gradualism Model: Slow and steady change from one species to another.

Pace of Speciation

2) Punctuated Equilibrium: Long periods of no change are followed by short periods of rapid change

Fossil RecordsHow do Both Models Explain the lack of Transition Fossils in

the Fossil Record?Phyletic Gradualism: The change from one species to

another is the result of reproductive isolation (RI). RI cannot be seen in the fossil record so we can’t tell if two similar organisms are able to reproduce. Therefore we cannot tell if they are different species?

Punctuated Equilibrium: Because the new species forms suddenly there are few individuals that show the transition from the old species to the new species

Assignment

• Questions