Macroevolution & Speciation Biology Honors
Speciation - Essential Question How can microevolution lead to the emergence of new species over time?
Review: Microevolution Focuses on the change in genetic frequencies for a trait in the population over time.
Macroevolution Accumulation of small genetic changes over time leads to speciation Formation of a new species No longer able to breed with each other
What is a species? A population of organisms who can interbreed with each other and produce viable (surviving), fertile (capable of reproducing) offspring
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)
Pre-Zygotic Barrier: Temporal Isolation Populations breed during different times Ex: frogs
Pre-Zygotic Barrier: Behavioral Isolation Populations respond to different mating cues Ex: blue footed booby dance (see video)
Pre-Zygotic Barrier: Habitat Isolation Populations are geographically separated Ex: Grand Canyon squirrels
Pre-Zygotic Barrier: Mechanical Isolation Reproductive parts are incompatible Ex: Pollinators and plants
Pre-Zygotic Barrier: Gametic Isolation Gametes of different species don’t recognize each other and join Ex: Ocean organisms
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
Extra help? Crash Course – Speciation