Evolutionary Theory and Speciation in Galápagos Islands

1. Chapter 24

2. In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth Overview: That “Mystery of Mysteries”

4. Galapagos Tortoises Blue footed boobie

5. Sea Lions

6. Marine Iguanas

7. Land Iguanas

8. Mockingbirds Hood Long-tailed

9. Finches Cactus finch Medium ground finch

10. Speciation, the origin of new species, is at the focal point of evolutionary theory Evolutionary theory must explain how new species originate and how populations evolve Microevolution consists of adaptations that evolve within a population, confined to one gene pool Macroevolution refers to evolutionary change above the species level

11. The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations The Biological Species Concept

12. Fig. 24-2a (a) Similarity between different species

13. Fig. 24-2b (b) Diversity within a species

14. Fig. 24-3a EXPERIMENT Example of a gene tree for population pair A-B Allele Population Gene flow event 1 B Allele 1 is more closely related to alleles 2, 3, and 4 than to alleles 5, 6, and 7. Inference: Gene flow occurred. 2 A A 3 4 A 5 B Alleles 5, 6, and 7 are more closely related to one another than to alleles in population A. Inference: No gene flow occurred. 6 B B 7

15. Fig. 24-3b RESULTS Pair of populations with detected gene flow Estimated minimum number of gene flow events to account for genetic patterns Distance between populations (km) A-B 5 340 K-L 3 720 A-C 2–3 1,390 2 B-C 1,190 F-G 2 760 2 1,110 G-I C-E 1–2 1,310

16. Fig. 24-3c Grey-crowned babblers

17. Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring Hybrids are the offspring of crosses between different species Reproductive isolation can be classified by whether factors act before or after fertilization Reproductive Isolation

18. Prezygotic barriers block fertilization from occurring by: Impeding different species from attempting to mate Preventing the successful completion of mating Hindering fertilization if mating is successful

19. Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers Water-dwelling Thamnophis Terrestrial Thamnophis

20. Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes Eastern spotted skunk (Spilogale putorius) Western spotted skunk (Spilogale gracilis)

21. Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers Courtship ritual of blue-footed boobies

22. Mechanical isolation: Morphological differences can prevent successful mating (f) Bradybaena with shells spiraling in opposite directions

23. Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species Sea urchins Corals

24. Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown

25. Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development Ensatina eschscholtzii Ensatina klauberi Ensatina hybrid

26. Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile Horse Donkey Mule (sterile hybrid)

27. Hybrid breakdown: Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile Hybrid cultivated rice plants with stunted offspring (center)

28. The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes) Limitations of the Biological Species Concept

29. Other species concepts emphasize the unity within a species rather than the separateness of different species The morphological species concept defines a species by structural features It applies to sexual and asexual species but relies on subjective criteria Other Definitions of Species

30. The ecological species concept views a species in terms of its ecological niche It applies to sexual and asexual species and emphasizes the role of disruptive selection The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species

31. Speciation can occur in two ways: Allopatric speciation Sympatric speciation Concept 24.2: Speciation can take place with or without geographic separation

32. Fig. 24-5 (a) Allopatric speciation (b) Sympatric speciation

33. In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations Allopatric (“Other Country”) Speciation

34. The definition of barrier depends on the ability of a population to disperse Separate populations may evolve independently through mutation, natural selection, and genetic drift The Process of Allopatric Speciation

35. Fig. 24-6 A. harrisi A. leucurus

36. Regions with many geographic barriers typically have more species than do regions with fewer barriers Evidence of Allopatric Speciation

37. Fig. 24-7 Mantellinae (Madagascar only): 100 species Rhacophorinae (India/Southeast Asia): 310 species Other Indian/ Southeast Asian frogs 100 60 20 80 40 0 1 2 3 Millions of years ago (mya) 1 3 2 India Madagascar 56 mya 88 mya 65 mya

38. Reproductive isolation between populations generally increases as the distance between them increases

39. Fig. 24-8 2.0 1.5 Degree of reproductive isolation 1.0 0.5 0 200 250 0 50 100 150 300 Geographic distance (km)

40. Barriers to reproduction are intrinsic; separation itself is not a biological barrier

41. Fig. 24-9 EXPERIMENT Initial population Some flies raised on starch medium Some flies raised on maltose medium Mating experiments after 40 generations RESULTS Female Female Starch Starch Starch Maltose population 2 population 1 Starch population 1 15 22 9 18 Starch Male Male 20 12 15 8 Maltose Starch population 2 Mating frequencies in experimental group Mating frequencies in control group

42. In sympatric speciation, speciation takes place in geographically overlapping populations Sympatric (“Same Country”) Speciation

43. Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division An autopolyploid is an individual with more than two chromosome sets, derived from one species Polyploidy

44. Fig. 24-10-1 2n = 6 4n = 12 Failure of cell division after chromosome duplication gives rise to tetraploid tissue.

45. Fig. 24-10-2 2n 2n = 6 4n = 12 Failure of cell division after chromosome duplication gives rise to tetraploid tissue. Gametes produced are diploid..

46. Fig. 24-10-3 2n 2n = 6 4n = 12 4n Failure of cell division after chromosome duplication gives rise to tetraploid tissue. Gametes produced are diploid.. Offspring with tetraploid karyotypes may be viable and fertile.

47. An allopolyploid is a species with multiple sets of chromosomes derived from different species

48. Fig. 24-11-1 Species B 2n = 4 Unreduced gamete with 4 chromosomes Meiotic error Normal gamete n = 3 Species A 2n = 6

49. Fig. 24-11-2 Species B 2n = 4 Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Meiotic error Normal gamete n = 3 Species A 2n = 6

50. Fig. 24-11-3 Species B 2n = 4 Unreduced gamete with 4 chromosomes Unreduced gamete with 7 chromosomes Hybrid with 7 chromosomes Meiotic error Normal gamete n = 3 Normal gamete n = 3 Species A 2n = 6