* Speciation occurs when a single ancestral group splits into two or more species * Results from genetic isolation and genetic divergence * How are species defined and identified * Biological species concept * Reproductive isolation * Prezygotic * Temporal * Habitat * Behavioral * Gametic barrier * Mechanical * Postzygotic * Hybrid viability * Hybrid sterility * Morphological species concept * Phylogenetic species concept * Monophyletic groups defined by synapomorphy * Case study: seaside sparrow * Isolation and divergence in allopatry * Allopatric speciation * Dispersal * Vicariance * Isolation and divergence in sympatry * Sympatric speciation * Disruptive selection * Polyploidy * Autopolyploidy * Allopolyploidy * Genetic consequences of polyploidy in plants * Secondary contact * Fusion * Reinforcement * Hybrid zones * Ring species * Hybrid speciation * Extinction of one population
Study Questions
1. Of the four evolutionary processes (gene flow, genetic drift, mutation, and natural selection), which contribute the most to speciation and which contribute the least? Or, how does each process affect speciation? 2. Describe three species concepts: under each concept, how is a species defined? How are they similar and how do they differ? 3. What is reproductive isolation? How can it be measured or determined? 4. Compare prezygotic and postzygotic reproductive isolation. What are some examples of each? 5. When does the biological species concept fail? 6. When does the morphological species concept fail? 7. What are some advantages and disadvantages of the phylogenetic species concept? 8. What is a monophyletic group? How are they determined? 9. In the seaside sparrow, how many subspecies are there under each species concept. Which concept do you feel is the most applicable to this example? What conservation strategy would you use to protect them from extinction? 10. Compare and contrast allopatric speciation with sympatric speciation. 11. Describe two ways in which allopatric speciation occurs. 12. Compare speciation by vicariance to speciation by dispersal. How are they different and how are they similar? What evolutionary processes are likely to be involved in each? 13. Under what conditions is sympatric speciation likely to occur? 14. How are autopolyploid individuals formed? How are allopolyploid individuals formed? 15. Why are polyploid species generally reproductively isolated from the parent species after only one generation? 16. Describe five possible outcomes of secondary contact between two isolated populations. 17. What is reinforcement? What is the primary cause of reinforcement and how is reproductive isolation maintained? 18. Why might hybrid zones be stable over time? 19. Why is mitochondrial DNA data useful in evaluating the dynamics of hybridization? Consider the example of the Townsend’s and hermit warblers. 20. What is a ring species? Describe an example. What makes them difficult to categorize using any of the species concepts? 21. What evidence supports the hypothesis that Helianthus anomalous was created through hybrid speciation?
