9.2 Speciation ( How Species Form)

What are species?

• Organisms that can breed with each other and produce fertile offspring’s

What is Speciation?

• Formation of a new species from existing species also called (macroevolution)

How does new species form?

• Reproductive Isolation - Pre zygotic - post zygotic

• Speciation - allopatric/sympatric

Reproductive Isolation

• Little or no gene flow between population

• 2 types

• Pre zygotic isolation

• Post zygotic isolation

5 Types of Pre Zygotic isolation

• 1.Behavioural Isolation

  - special mating behaviours, signals or chemicals (pheramones)

  that a species may use in courtship may not be the same ones

  that other species use

  - Example: Eastern & Western Meadow Lark live in the same

  area but they have different mating songs (whistle like vs. flute

  like)

  2.Habitat Isolation

  - Animals live in different habitats and rarely meeting each other

  - Example: North American garter snake (prefer open areas) and

  the North Western garter snake (prefer water)

  Pre-Zygotic Isolation

  3. Temporal Isolation

  - occupy the same environment but the time for mating

  or flowering is different

  - Example: Orchids (dendrobium) bloom at different

  times depending on weather

  4. Mechanical Isolation

  - reproductive parts are anatomically incompatible

  5. Gametic Isolation

  - egg and sperm of the different organisms do not fuse

  together

3 Types of Post Zygotic isolating mechanisms

• 1.Hybrid Inviability - genetic incompatibility, hybrid dies

  before birth (error in mitosis)

  - Example: Sheep and Goats

  2.Hybrid Sterility – offspring is born, but is infertile

  - Example: mule (mix of horse and donkey)

  3.Hybrid Breakdown – hybrid reproduces but next

  generation is weak/sterile

What is Sympatric Speciation?

• Occurs when populations become reproductively isolated genetically

• Example: changed offspring can no longer mate with the

  unchanged group which results in a new species within 1

  generation

Allopatric speciation

• Populations is split into 2 or more isolated groups by a geographical barrier

• Glacier/lava flow/earthquake

• Isolated populations become very different with time due to Natural selection/mutation/genetic drift

Example:• squirrels on either side of the canyon are different species

• birds on either side of the canyon are the same species

Why?

- squirrels cannot cross the canyon but birds can which means they can mate with other birds and share genes with birds that are on the other side of the canyon

Adaptive Radiation

• Occurs when a common ancestral species has diversified into a variety of different adaptive species to form allopatric speciation

What is divergent evolution?

• Species once similar to ancestral forms diverge to become increasingly distant

• Occurs when populations change as they adapt to the environments

What is convergent Evolution'?

• Two unrelated species share similar traits but adapted to similar environmental conditions

• Example - bats and birds

What is Co Evolution?

• Some organisms have evolved gradually together in response to changes in each other and have become linked together

• Examples

• Predators and prey

• Pollinators and plants

• Parasites and hosts