Speciation

Objectives:1. Define the term speciation and explain what it means.

2. Describe two different modes of speciation.3. Explain what extinction is and how it happens.

Other Mechanisms that Drive Evolution

• Sexual Selection: the process by which a trait that enables an organism to acquire more mates becomes more common.

• Males compete for females (combat)

• Females chose males (desirable traits)

How many different types of living things are there on Earth?

Do members of the same species look exactly the same?

7D Variation – What is a species?

Scientists have identified almost 2 million different types of living things.

Each different type of living thing is called a species.

Many more are yet to be discovered and scientists estimate there could be up to 30 million different types of living things!

7D Variation – Similar but different

A species is a group of living things with similar features.

• Members of the same species can breed together to produce fertile offspring.

• Members of different species cannot interbreed under normal conditions.– We say they are reproductively isolated from each

other.

7D Variation – Similar but different

Name 5 ways in which these dogs are similar.

Name 5 ways in which these dogs are different.

Differences between members of the same species are called variation.

7D Variation – What is variation?

7D Variation – Causes of variation

Which type of variation is described by each definition?

A This type of variation is passed on in genes from parent to offspring.

B This type of variation is influenced

by living conditions and surroundings.

Variation is caused by environmental or inherited factors.

environmentalinherited

Environmental variation is caused by differences in living conditions and surroundings.

Climate and food supply are environmental factors that influence all living things.

How might these environmental factors cause variation?

7D Variation – Environmental factors

Invisible Differences...

• Disease resistance: Some fruit are resistant to certain diseases. – Green Anjou pears are more resistant to a disease

called fireblight.• If they were attacked by this disease they would be less

likely to get it.

• BUT ... You can’t tell this just by looking at the pears can you???

Why do different organisms live in different environments??

• Different organisms are adapted to live in certain environments.

• An adaptation is a trait or characteristic that enables an organism to survive.

• These adaptations are then passed on to their offspring.

Overtime, so many adaptations or differences may accumulate that individuals can no longer interbreed and have to be considered a difference species.

Speciation

• A new species is formed when two populations of plants or animals accumulate so many genetic changes (mutations, adaptations) that they cannot interbreed and produce fertile offspring.

Modes of Speciation…

• These processes all include the evolution of distinct features that isolate the new species reproductively and as a result genetically fro the original species.

1. Reproductive isolation2. Allopatric Speciation3. Sympatric Speciation

1. Reproductive Isolation

Individuals are prevented from breeding together because of behavioural, structural or biochemical traits.- Behavioural: Different courtship displays, different breeding seasons or different habitats- Structural: Different/Incompatible genitalia- Biochemical: Male gamete may not recognize female gamete.

Pre and Post zygotic mechanisms• Prezygotic mechanisms prevent fertilization and

zygote formation.– Behaviour isolation– Temporal isolation– Ecological or Geographical isolation– Mechanical or Gametic isolation

• Postzygotic mechanisms prevent a fertilized egg from developing.– Hybrid in viability– Hybrid sterility or breakdown

2. Allopatric SpeciationA new species develops after being geographically separated from the original population.a) They can no longer exchange genetic informationb) Any mutation that arises in one population is not

shared with the otherc) Differences in environments may lead to

differences in natural selectionOther differences such as courtship displays and breeding season may evolve.

The scene: a population of wild fruit flies minding its own business on several bunches of rotting bananas, cheerfully laying their eggs in the mushy fruit... Disaster strikes: A hurricane washes the bananas and the immature fruit flies they contain out to sea. The banana bunch eventually washes up on an island off the coast of the mainland. The fruit flies mature and emerge from their slimy nursery onto the lonely island. The two portions of the population, mainland and island, are now too far apart for gene flow to unite them. At this point, speciation has not occurred — any fruit flies that got back to the mainland could mate and produce healthy offspring with the mainland flies.

The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does. Morphology, food preferences, and courtship displays change over the course of many generations of natural selection.

So we meet again: When another storm reintroduces the island flies to the mainland, they will not readily mate with the mainland flies since they've evolved different courtship behaviors. The few that do mate with the mainland flies, produce inviable eggs because of other genetic differences between the two populations. The lineage has split now that genes cannot flow between the populations.

3. Sympatric Speciation..

New species are formed when individuals within a larger population become genetically isolated.- More common in plants than in animals.- Can be gradual ______________- Can be sudden such as when a mutation

affects a few individuals of a population preventing them from mating with others.

Extinction

• Why are there fossils of organisms that don’t exist today?

• Why do you think organisms go extinct?

• Through evolution, new species arise through the process of speciation – New varieties of organisms arise and thrive when

they are able to survive in an environment

• Species become extinct when they are no longer able to survive in changing conditions or against superior competition.

What causes extinction• Any species that is …

– unable to survive or reproduce in its environment• Extinction of a species may come suddenly

when an otherwise healthy species is wiped out completely.– Pesticides make insects food uneatable– New predator is introduced and animal can’t

escape– Disease wipes out species

Plenary

• 1. Explain what speciation means.• 2. What are three different modes of

speciation?• 3. How can individuals of a species become

reproductively isolated?• 4. What is the difference between allopatric

speciation and sympatric speciation.

Your Task

• Read through your handout on ‘Speciation’ and answer questions 1 to 5.

• Question to consider…• Cheetahs have very little genetic variation from

individual to individual. Based on Darwin’s theory of natural selection, how might this influence the evolution of the species?

• Species with very little genetic variation have an increased risk of becoming extinct. Why?