EEB2245W S2009 Review Questions

Review Questions for 16 March 2009 (Geographic Variation and Speciation)

What is speciation? Why is speciation said to be a bridge between microevolution and macroevolution?

What evolutionary processes have likely been responsible for divergence in Ensatina? What evidence shows that these have been important?

In general, what factors tend to promote divergence of populations? What factors tend to prevent divergence?

Why is Ensatina eschscholtzii treated as a single species even though the southern forms are reproductively isolated from each other?

How did reproductive isolation evolve in Ensatina?

What is the significance of the three evolutionary experiments in Ensatina?

       experiment 1 = closing of the ring in southern California 
       experiment 2 = Spread of solid forms across the Central Valley and into contact with the blotched forms in the Sierra Nevada 
       experiment 3 = extinction experiment--what would be the effect of extinction of the northern California populations?

Compare the role of natural selection in generating geographic variants in Ensatina and Plestiodon. What is the role of natural selection in the evolution of reproductive isolation in each of these examples?

Thought question: Why can't natural selection act directly to produce postzygotic isolation between populations?