EEB2245W S2009 Review Questions

Review Questions for 19 March 2009 (Mechanisms of Speciation)

What argument would you give for the existence of 4 species of Plestiodon in California? How about 2 species? And 1 species? Which of these is arguments do you think is strongest? Why?

Define and give examples of prezygotic and postzygotic reproductive isolation.

What is the first step in allopatric speciation?

Why do the genetic models of the evolution of postzygotic reproductive isolation involve at least two genetic changes?

What is epistasis? What is its role in speciation?

What role does natural selection play in speciation according to the Dobzhansky-Muller model?

Why do we expect reproductive isolation to evolve if populations are isolated for long enough?

Give examples of genes known to contribute to low fitness in hybrids. Do these examples suggest that there is a special class of "speciation genes" that are responsible for the evolution of reproductive isolation?

Thought question: We looked at the 3D fitness landscape for a model of speciation by natural selection. A very similar model in which genetic changes are due to drift can also lead to speciation. How would the fitness landscape be similar if the changes in each of the populations were caused by drift? How would it be different?

Review Questions for 17 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?