BIOE 109 Summer 2009 Lecture 11-Part II Speciation

1. BIOE 109 Summer 2009 Lecture 11-Part II Speciation

2. What is speciation?

3. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”.

4. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms.

5. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. • the barriers may act to prevent fertilization – this is pre-zygotic isolation.

6. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. • the barriers may act to prevent fertilization – this is pre-zygotic isolation. • may involve changes in location or timing of breeding, or courtship.

7. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. • the barriers may act to prevent fertilization – this is pre-zygotic isolation. • may involve changes in location or timing of breeding, or courtship. • barriers also occur if hybrids are inviable or sterile – this is post-zygotic isolation.

8. Modes of Speciation

9. Modes of Speciation 1. Allopatric speciation

10. Modes of Speciation 1. Allopatric speciation • reproductive isolation occurs in complete geographic isolation.

11. Modes of Speciation 1. Allopatric speciation • reproductive isolation occurs in complete geographic isolation (no gene flow).

12. Geographic isolation can rise from dispersal or vicariance

13. Modes of Speciation 1. Allopatric speciation • reproductive isolation occurs in complete geographic isolation (no gene flow). Example: Hawaiian Drosophila

14. Hawaiian Drosophila D. suzukii D. microthrix D. nigribasis

15. Speciation by island-hopping

16. Modes of Speciation 2. Parapatric speciation

17. Modes of Speciation 2. Parapatric speciation • reproductive isolation occurs without complete geographic isolation (some gene flow).

18. Modes of Speciation 2. Parapatric speciation • reproductive isolation occurs without complete geographic isolation (some gene flow). Example: ring species of salamanders (Ensatina) in CA

19. Ensatina salamanders

20. Ring species – evidence for parapatric speciation

21. Ring species – evidence for parapatric speciation

22. Modes of Speciation 3. Sympatric speciation

23. Modes of Speciation 3. Sympatric speciation • reproductive isolation evolves with complete geographic overlap.

24. Modes of Speciation 3. Sympatric speciation • reproductive isolation evolves with complete geographic overlap. Example: the apple maggot fly, Rhagoletis pomonella?

25. Apple maggot fly Hawthorn fly Speciation due to host specialization in this case

26. Modes of speciation: summary Allopatric peripatric parapatric sympatric Original population Initial step of speciation Barrier formation New niche New niche Genetic polymorphism Evolution of reproductive isolation In isolation In isolation In adjacent niche Within the population

27. What evolutionary processes are involved in speciation?

28. What evolutionary processes are involved in speciation? 1. Natural selection

29. What evolutionary processes are involved in speciation? 1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites).

30. What evolutionary processes are involved in speciation? 1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). 2. Sexual selection

31. What evolutionary processes are involved in speciation? 1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). 2. Sexual selection • both female choice and male-male competition can promote rapid divergence (e.g., Hawaiian Drosophila).

32. What evolutionary processes are involved in speciation? 1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). 2. Sexual selection • both female choice and male-male competition can promote rapid divergence (e.g., Hawaiian Drosophila). • sexual antagonistic selection too!

33. Male-male competition in Hawaiian Drosophila Establish territory On a lek by head butting Fight over display Territory by grappling

34. What evolutionary processes are involved in speciation? 3. Random genetic drift

35. What evolutionary processes are involved in speciation? 3. Random genetic drift • may involve founder effects and genetic bottlenecks.

36. What evolutionary processes are involved in speciation? 3. Random genetic drift • may involve founder effects and genetic bottlenecks. • alleles that are neutral in one environment may not be neutral in another!

37. Some generalities 1. The magnitude of pre-zygotic and post-zygotic isolation both increase with the time.

38. Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the time. • in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve.

39. Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the time. • in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve. • in marine bivalves, it may take 4 to 6 million years!

40. Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the time. • in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve. • in marine bivalves, it may take 4 to 6 million years! 2. Among recently separated groups, pre-zygotic isolation is generally stronger than post-zygotic isolation.

41. Some generalities 3. In the early stages of speciation, hybrid sterility or inviability is almost always seen in the heterogametic sex.

42. Some generalities 3. In the early stages of speciation, hybrid sterility or inviability is almost always seen in the heterogametic sex. • for example, D. simulans and D. mauritiana female hybrids are completely viable yet male hybrids are completely sterile!

43. Some generalities 3. In the early stages of speciation, hybrid sterility or inviability is almost always seen in the heterogametic sex. • for example, D. simulans and D. mauritiana female hybrids are completely viable yet male hybrids are completely sterile! • this is called Haldane’s rule. J.B.S. Haldane (1892-1964)

44. What causes post-zygotic isolation?

45. What causes postzygotic isolation? • the underlying mechanism is called Dobzhansky-Muller incompatibility:

46. Dobzhansky and Muller were incompatible! “Classical” school “Balanced” school

47. What causes postzygotic isolation? • the underlying mechanism is called Dobzhansky-Muller incompatibility: Ancestral Pop: A1A1B1B1

48. What causes postzygotic isolation? • the underlying mechanism is called Dobzhansky-Muller incompatibility: Ancestral Pop: A1A1B1B1  Derived Pops: A2A2B1B1 A1A1B2B2

49. What causes postzygotic isolation? • the underlying mechanism is called Dobzhansky-Muller incompatibility: Ancestral Pop: A1A1B1B1  Derived Pops: A2A2B1B1 A1A1B2B2  Hybrids: A1A2B1B2 fitness

50. Differences between plant and animal speciation