1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick The Origin of Species Chapter 24

2. How did this flightless bird come to live on the isolated Galápagos Islands?

3. Speciation, the origin of new species, is at the focal point of evolutionary theory Scale of evolution: Microevolution consists of changes in allele frequency in a population over time Macroevolution refers to broad patterns of evolutionary change above the species level © 2011 Pearson Education, Inc. Process of species change

4. Concept 24.1: The biological species concept emphasizes reproductive isolation Biological Species Concept (one way to divide species): –A species is a group of populations whose members can breed and produce viable, fertile offspring –Ability to mate = formation of a species –Gene flow between populations holds together the phenotype of a population (ongoing exchange of alleles) © 2011 Pearson Education, Inc.

5. It’s all about ability to breed (a) Similarity between different species (b) Diversity within a species

6. Reproductive Isolation is the driving force behind Speciation A new species will form when reproductive isolation occurs –Absence of gene flow Reproductive Isolation: –The existence of biological factors (barriers) that prevent two individuals of a species from mating and producing viable and fertile offspring Hybrids: –Offspring of crosses between two different species Barriers may contribute to reproductive isolation before or after fertilization (pre- or postzygotic barriers) © 2011 Pearson Education, Inc.

7. 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 –5 types of prezygotic barriers © 2011 Pearson Education, Inc.

8. Figure 24.3_b Prezygotic barriers Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation Gametic Isolation Individuals of different species MATING ATTEMPT FERTILIZATION (a) (c) (e) (f) (b) (g) (d)

9. Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: –Reduced hybrid viability –Reduced hybrid fertility –Hybrid breakdown © 2011 Pearson Education, Inc.

10. Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown FERTILIZATION VIABLE, FERTILE OFFSPRING Postzygotic barriers (k) (h) (i) (j) (l) Figure 24.3_c

11. Limitations of the Biological Species Concept The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes) The biological species concept emphasizes absence of gene flow However, gene flow can occur between distinct species –For example, grizzly bears and polar bears can mate to produce “grolar bears” © 2011 Pearson Education, Inc.

12. Figure 24.4 Grizzly bear (U. arctos) Polar bear (U. maritimus) Hybrid “grolar bear”

13. Other Definitions of Species 1. morphological species concept: –A species is characterized by its body shape –It applies to sexual and asexual species but relies on subjective criteria 2. ecological species concept: –A species is characterized by its ecological niche –It applies to sexual and asexual species and emphasizes the role of disruptive selection 3. phylogenetic species concept: –A species is the smallest group of individuals that share a common ancestor –It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species © 2011 Pearson Education, Inc.

14. Video: Albatross Courtship Ritual

15. © 2011 Pearson Education, Inc. Video: Giraffe Courtship Ritual

16. © 2011 Pearson Education, Inc. Video: Blue-footed Boobies Courtship Ritual

17. Concept 24.2: Speciation can take place with or without geographic separation Speciation can occur in two ways: –Allopatric speciation –Sympatric speciation What do the route words mean? © 2011 Pearson Education, Inc.

18. Figure 24.5 (a) (b) Allopatric speciation. A population forms a new species while geographically isolated from its parent population. Sympatric speciation. A subset of a population forms a new species without geographic separation.

19. Allopatric (“Other Country”) Speciation In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations –For example, the flightless cormorant of the Galápagos likely originated from a flying species on the mainland © 2011 Pearson Education, Inc.

20. The Process of Allopatric Speciation The definition of barrier depends on the ability of a population to disperse –For example, a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen © 2011 Pearson Education, Inc. A. harrisiiA. leucurus

21. Once isolated: Separate populations may evolve independently through mutation, natural selection, and genetic drift Reproductive isolation may arise as a result of genetic divergence –For example, mosquitofish in the Bahamas comprise several isolated populations in different ponds © 2011 Pearson Education, Inc.

22. Figure 24.7 (a) Under high predation (b) Under low predation

23. Evidence of Allopatric Speciation: a case study 15 pairs of sibling species of snapping shrimp (Alpheus) are separated by the Isthmus of Panama These species originated 9 to 13 million years ago, when the Isthmus of Panama formed and separated the Atlantic and Pacific waters © 2011 Pearson Education, Inc.

24. Figure 24.8 A. formosus Atlantic Ocean A. nuttingi Isthmus of Panama Pacific Ocean A. panamensisA. millsae

25. What types of regions have the greatest isolation? © 2011 Pearson Education, Inc.

26. What types of regions have the greatest isolation? Reproductive isolation between populations generally increases as the distance between them increases –For example, reproductive isolation increases between dusky salamanders that live further apart © 2011 Pearson Education, Inc.

27. Dusky salamanders Degree of reproductive isolation Geographic distance (km) 0 50 100 150 200 250 300 2.0 1.5 1.0 0.5 0

28. Figure 24.10 EXPERIMENT RESULTS Initial population of fruit flies (Drosophila pseudoobscura) Some flies raised on starch medium Mating experiments after 40 generations Some flies raised on maltose medium Female Starch Maltose Male Maltose Starch Number of matings in experimental group 22 9 8 20 Female Starch population 1 Male Starch population 2 Number of matings in control group 18 15 12 15 Starch population 2 Starch population 1

29. Sympatric (“Same Country”) Speciation In sympatric speciation, speciation takes place in geographically overlapping populations How can this occur if parent species is in same area? Provide an example. © 2011 Pearson Education, Inc.

30. Sympatric (“Same Country”) Speciation In sympatric speciation, speciation takes place in geographically overlapping populations In a sympatric speciation, various factors can limit gene flow: –Polyploidy –Habitat differentiation –Sexual selection © 2011 Pearson Education, Inc.

31. Polyploidy Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division –Polyploidy is much more common in plants than in animals. Why do you think? An autopolyploid is an individual with more than two chromosome sets, derived from one species –When would this originate? An allopolyploid is a species with multiple sets of chromosomes derived from different species (see diagram on proceeding slides) © 2011 Pearson Education, Inc.

32. Figure 24.11-1 Species A 2n = 6 Species B 2n = 4 Normal gamete n = 3 Meiotic error; chromosome number not reduced from 2n to n Unreduced gamete with 4 chromosomes

33. Figure 24.11-2 Species A 2n = 6 Species B 2n = 4 Normal gamete n = 3 Meiotic error; chromosome number not reduced from 2n to n Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes

34. Figure 24.11-3 Species A 2n = 6 Species B 2n = 4 Normal gamete n = 3 Meiotic error; chromosome number not reduced from 2n to n Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Unreduced gamete with 7 chromosomes Normal gamete n = 3

35. Figure 24.11-4 Species A 2n = 6 Species B 2n = 4 Normal gamete n = 3 Meiotic error; chromosome number not reduced from 2n to n Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Unreduced gamete with 7 chromosomes Normal gamete n = 3 New species: viable fertile hybrid (allopolyploid) 2n = 10

36. Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids © 2011 Pearson Education, Inc.

37. Habitat Differentiation Sympatric speciation can also result from the appearance of new ecological niches For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees © 2011 Pearson Education, Inc.

38. Normal light Monochromatic orange light P. pundamilia P. nyererei EXPERIMENT Sexual Selection : Sexual selection for mates of different colors has likely contributed to speciation in cichlid fish in Lake Victoria

39. Allopatric and Sympatric Speciation: A Review In allopatric speciation, geographic isolation restricts gene flow between populations Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations –Even if contact is restored between populations, interbreeding is prevented © 2011 Pearson Education, Inc.

40. In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species –Sympatric speciation can result from polyploidy, natural selection, or sexual selection © 2011 Pearson Education, Inc.

41. Concept 24.3: Hybrid zones reveal factors that cause reproductive isolation A hybrid zone is a region in which members of different species mate and produce hybrids Can you think of an example of where and how this would occur? © 2011 Pearson Education, Inc.

42. Patterns Within Hybrid Zones A hybrid zone can occur in a single band where adjacent species meet –For example, two species of toad in the genus Bombina interbreed in a long and narrow hybrid zone (see next slide) –Would you expect hybrids to have more, less and the same fitness as the parents? © 2011 Pearson Education, Inc.

43. Figure 24.13 EUROPE Yellow-bellied toad, Bombina variegata Fire-bellied toad range Hybrid zone Yellow-bellied toad range Fire-bellied toad, Bombina bombina Frequency of B. variegata-specific allele Yellow-bellied toad range Hybrid zone Fire-bellied toad range Distance from hybrid zone center (km) 40 0.99 0.9 0.5 0.1 0.01 30 20 100 20

44. Figure 24.13b Frequency of B. variegata-specific allele Yellow-bellied toad range Hybrid zone Fire-bellied toad range Distance from hybrid zone center (km) 40 0.99 0.9 0.5 0.1 0.01 30 20 100 20

45. Hybrid Zones over Time When closely related species meet in a hybrid zone, there are three possible outcomes: –Reinforcement –Fusion –Stability © 2011 Pearson Education, Inc.

46. Figure 24.14-1 Gene flow Population Barrier to gene flow

47. Formation of a hybrid zone and possible outcomes for hybrids over time. Gene flow Population Barrier to gene flow Isolated population diverges

48. Figure 24.14-3 Gene flow Population Barrier to gene flow Isolated population diverges Hybrid zone Hybrid individual

49. Figure 24.14-4 Gene flow Population Barrier to gene flow Isolated population diverges Hybrid zone Hybrid individual Possible outcomes: Reinforcement OR Fusion Stability

50. Reinforcement: Strengthening Reproductive Barriers The reinforcement of barriers occurs when hybrids are less fit than the parent species Over time, the rate of hybridization decreases Where reinforcement occurs, reproductive barriers should be stronger for sympatric than allopatric species –For example, in populations of flycatchers, males are more similar in allopatric populations than sympatric populations © 2011 Pearson Education, Inc.

51. Figure 24.15 Females choosing between these males: Females choosing between these males: Sympatric pied male Sympatric collared male Allopatric pied male Allopatric collared male (none) Female mate choice Own species Own species Other species Other species Number of females 28 24 20 16 12 8 4 0

52. Fusion: Weakening Reproductive Barriers If hybrids are as fit as parents, there can be substantial gene flow between species –How would increasing gene flow affect separate species? For example, researchers think that pollution in Lake Victoria has reduced the ability of female cichlids to distinguish males of different species –How would this affect different cichlid species? © 2011 Pearson Education, Inc.

53. Figure 24.16 Pundamilia nyererei Pundamilia pundamilia Pundamilia “turbid water,” hybrid offspring from a location with turbid water

54. Concept 24.4: Speciation can occur rapidly or slowly and can result from changes in few or many genes © 2011 Pearson Education, Inc.

55. The Time Course of Speciation By what tools can we determine rate of speciation? © 2011 Pearson Education, Inc.

56. The Time Course of Speciation By what tools can we determine rate of speciation? –fossil record, –morphological data, or –molecular data © 2011 Pearson Education, Inc.

57. Patterns in the Fossil Record The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibria to describe periods of apparent stasis punctuated by sudden change –Compare punctuated equlibrium to uniformitarianism. –Which model is more correct? © 2011 Pearson Education, Inc.

58. Figure 24.17 (a) Punctuated pattern Time (b) Gradual pattern Represent these two models in graphic form

59. Speciation Rates The punctuated pattern in the fossil record and evidence from lab studies suggest that speciation can be rapid –For example, the sunflower Helianthus anomalus originated from the hybridization of two other sunflower species © 2011 Pearson Education, Inc.

60. Figure 24.18

61. How does hybridization lead to speciation in sunflowers?? H. annuus gamete H. petiolarus gamete F 1 experimental hybrid (4 of the 2n = 34 chromosomes are shown) EXPERIMENT RESULTS Chromosome 1 H. anomalus Chromosome 2 H. anomalus Experimental hybrid

62. Average rates of speciation The interval between speciation events can range from 4,000 years (some cichlids) to 40 million years (some beetles), with an average of 6.5 million years © 2011 Pearson Education, Inc.

63. Studying the Genetics of Speciation A fundamental question of evolutionary biology persists: How many genes change when a new species forms? For example: In Japanese Euhadra snails, the direction of shell spiral affects mating and is controlled by a single gene In monkey flowers (Mimulus), two loci affect flower color, which influences pollinator preference –Pollination that is dominated by either hummingbirds or bees can lead to reproductive isolation of the flowers © 2011 Pearson Education, Inc.

64. Typical Mimulus lewisii (a) Typical Mimulus cardinalis (c) M. lewisii with an M. cardinalis flower-color allele (b) M. cardinalis with an M. lewisii flower-color allele (d) Figure 24.20

65. VOCAB REVIEW The cumulative effect of many speciation and extinction events is called ________________. The ____________species concept defines a species by structural features. The sudden change in a species after a long period of no change is called ____________.

66. Figure 24.UN01 Cell division error 2n = 6 4n = 12 2n2n 2n2n New species (4n) Gametes produced The new species would be called a ___________.

67. Figure 24.UN02 Original population _______ speciation ________ speciation Fill in the blanks

68. Answers to VOCAB REVIEW Macroevolution Morphological Punctuated equlibrium Polyploid, or tetraploid more specifically Allopatric Sympatric

69. TRY…Test Your Understanding, question 10

70. Figure 24.UN03 Ancestral species: Product: Triticum monococcum (2n = 14) Wild Triticum (2n = 14) Wild T. tauschii (2n = 14) T. aestivum (bread wheat) (2n = 42) Test Your Understanding, question 10

71. Figure 24.UN04