1. Macroevolution & Speciation
Biology Honors

2. Speciation - Essential Question
How can microevolution lead to the emergence of new species over time?

3. Review: Microevolution
Focuses on the change in genetic frequencies for a trait in the population over time.

4. Macroevolution
Accumulation of small genetic changes over time leads to speciation
Formation of a new species
No longer able to breed with each other

5. What is a species?
A population of organisms who can interbreed with each other and produce viable (surviving), fertile (capable of reproducing) offspring

6. Mechanisms for Macroevolution
Requires reproductive isolation
Pre-zygotic barriers
Barriers prior to reproduction (no zygote forms)
Post-zygotic barriers
Barriers after reproduction (no viable, fertile offspring)

7. Pre-Zygotic Barrier: Temporal Isolation
Populations breed during different times
Ex: frogs

8. Pre-Zygotic Barrier: Behavioral Isolation
Populations respond to different mating cues
Ex: blue footed booby dance (see video)

9. Pre-Zygotic Barrier: Habitat Isolation
Populations are geographically separated
Ex: Grand Canyon squirrels

10. Pre-Zygotic Barrier: Mechanical Isolation
Reproductive parts are incompatible
Ex: Pollinators and plants

11. Pre-Zygotic Barrier: Gametic Isolation
Gametes of different species don’t recognize each other and join
Ex: Ocean organisms

12. Post-Zygotic Barriers
Hybrid Inviability
Zygote forms but doesn’t develop
Hybrid Sterility
Hybrid offspring is not fertile
Hybrid Breakdown
Hybrid may be fertile but subsequent generations are not

13. Extra help?
Crash Course – Speciation