Big Idea #1 Part C

1. Big Idea #1 Part C Speciation and Extinction (Rates/adaptive radiation) Role of Reproductive Isolation Populations continue to evolve Evolution Continues in a Changing Environment

2. Concept 24.3: Hybrid zones provide opportunities to study factors that cause reproductive isolation • A hybrid zoneis a region in which members of different species mate and produce hybrids

3. Patterns Within Hybrid Zones • A hybrid zone can occur in a single band where adjacent species meet • Hybrids often have reduced fitness compared with parent species • The distribution of hybrid zones can be more complex if parent species are found in multiple habitats within the same region

4. Fig. 24-13 EUROPE Fire-bellied toad range Hybrid zone Fire-bellied toad, Bombina bombina Yellow-bellied toad range Yellow-bellied toad, Bombina variegata 0.99 0.9 Allele frequency (log scale) 0.5 0.1 0.01 20 40 30 10 0 10 20 Distance from hybrid zone center (km)

5. Fig. 24-13a Yellow-bellied toad, Bombina variegata

6. Fig. 24-13b Fire-bellied toad, Bombina bombina

7. Fig. 24-13c Fire-bellied toad range Hybrid zone Yellow-bellied toad range 0.99 0.9 Allele frequency (log scale) 0.5 0.1 0.01 20 10 0 40 30 20 10 Distance from hybrid zone center (km)

8. Hybrid Zones over Time When closely related species meet in a hybrid zone, there are three possible outcomes: • Strengthening of reproductive barriers • Weakening of reproductive barriers • Continued formation of hybrid individuals

9. Fig. 24-14-1 Gene flow Barrier to gene flow Population (five individuals are shown)

10. Fig. 24-14-2 Isolated population diverges Gene flow Barrier to gene flow Population (five individuals are shown)

11. Fig. 24-14-3 Isolated population diverges Hybrid zone Gene flow Hybrid Barrier to gene flow Population (five individuals are shown)

12. Fig. 24-14-4 Isolated population diverges Possible outcomes: Hybrid zone Reinforcement OR Fusion Gene flow Hybrid OR Barrier to gene flow Population (five individuals are shown) Stability

13. Reinforcement: Strengthening Reproductive Barriers • The reinforcementof 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

14. Fig. 24-15 Allopatric male pied flycatcher Sympatric male pied flycatcher 28 Pied flycatchers 24 Collared flycatchers 20 16 Number of females 12 8 4 (none) 0 Females mating with males from: Other species Own species Own species Other species Sympatric males Allopatric males

15. Fig. 24-15a Allopatric male pied flycatcher Sympatric male pied flycatcher

16. Fig. 24-15b 28 Pied flycatchers 24 Collared flycatchers 20 16 Number of females 12 8 4 (none) 0 Other species Own species Other species Females mating with males from: Own species Sympatric males Allopatric males

17. Fusion: Weakening Reproductive Barriers • If hybrids are as fit as parents, there can be substantial gene flow between species • If gene flow is great enough, the parent species can fuse into a single species

18. Fig. 24-16 Pundamilia nyererei Pundamilia pundamilia Pundamilia “turbid water,” hybrid offspring from a location with turbid water

19. Stability: Continued Formation of Hybrid Individuals • Extensive gene flow from outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone • In cases where hybrids have increased fitness, local extinctions of parent species within the hybrid zone can prevent the breakdown of reproductive barriers

20. Concept 24.4: Speciation can occur rapidly or slowly and can result from changes in few or many genes Many questions remain concerning how long it takes for new species to form, or how many genes need to differ between species

21. The Time Course of Speciation • Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular data

22. 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 equilibriumto describe periods of apparent stasis punctuated by sudden change • The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence

23. Fig. 24-17 (a) Punctuated pattern Time (b) Gradual pattern

24. Speciation Rates • The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation can be rapid • The interval between speciation events can range from 4,000 years (some cichlids) to 40,000,000 years (some beetles), with an average of 6,500,000 years

25. Fig. 24-18 (a) The wild sunflower Helianthus anomalus H. anomalus Chromosome 1 Experimental hybrid H. anomalus Chromosome 2 Experimental hybrid H. anomalus Chromosome 3 Experimental hybrid Key Region diagnostic for parent species H. annuus Region diagnostic for parent species H. petiolaris Region lacking information on parental origin (b) The genetic composition of three chromosomes in H. anomalus and in experimental hybrids

26. Fig. 24-18a (a) The wild sunflower Helianthus anomalus

27. Fig. 24-18b H. anomalus Chromosome 1 Experimental hybrid H. anomalus Chromosome 2 Experimental hybrid H. anomalus Chromosome 3 Experimental hybrid Key Region diagnostic for parent species H. petiolaris Region diagnostic for parent species H. annuus Region lacking information on parental origin (b) The genetic composition of three chromosomes in H. anomalus and in experimental hybrids

28. Studying the Genetics of Speciation • The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation • Depending on the species in question, speciation might require the change of only a single allele or many alleles

29. Fig. 24-19

30. Fig. 24-20 (a) Typical Mimulus lewisii (b) M. lewisii with an M. cardinalis flower-color allele (c) Typical Mimulus cardinalis (d) M. cardinalis with an M. lewisii flower-color allele

31. From Speciation to Macroevolution • Macroevolution is the cumulative effect of many speciation and extinction events

32. Fig. 24-UN1 Original population Allopatric speciation Sympatric speciation

33. Fig. 24-UN2 Ancestral species: AA BB DD Wild T. tauschii (2n = 14) Triticum monococcum (2n = 14) Wild Triticum (2n = 14) Product: AA BB DD T. aestivum (bread wheat) (2n = 42)

34. Fig. 24-UN3

35. You should now be able to: • Define and discuss the limitations of the four species concepts • Describe and provide examples of prezygotic and postzygotic reproductive barriers • Distinguish between and provide examples of allopatric and sympatric speciation • Explain how polyploidy can cause reproductive isolation • Define the term hybrid zone and describe three outcomes for hybrid zones over time

36. Concept 25.4: The rise and fall of dominant groups reflect continental drift, mass extinctions, and adaptive radiations • The history of life on Earth has seen the rise and fall of many groups of organisms Video: Volcanic Eruption Video: Lava Flow

37. Continental Drift • At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago • Earth’s continents move slowly over the underlying hot mantle through the process of continental drift • Oceanic and continental plates can collide, separate, or slide past each other • Interactions between plates cause the formation of mountains and islands, and earthquakes

38. Fig. 25-12 North American Plate Eurasian Plate Crust Caribbean Plate Philippine Plate Juan de Fuca Plate Arabian Plate Indian Plate Cocos Plate Mantle South American Plate Pacific Plate Nazca Plate African Plate Outer core Australian Plate Inner core Antarctic Plate Scotia Plate (b) Major continental plates (a) Cutaway view of Earth

39. Fig. 25-12a Crust Mantle Outer core Inner core (a) Cutaway view of Earth

40. Fig. 25-12b North American Plate Eurasian Plate Caribbean Plate Philippine Plate Juan de Fuca Plate Arabian Plate Indian Plate Cocos Plate South American Plate Pacific Plate Nazca Plate African Plate Australian Plate Antarctic Plate Scotia Plate (b) Major continental plates

41. Consequences of Continental Drift • Formation of the supercontinent Pangaeaabout 250 million years ago had many effects • A reduction in shallow water habitat • A colder and drier climate inland • Changes in climate as continents moved toward and away from the poles • Changes in ocean circulation patterns leading to global cooling

42. Fig. 25-13 Present Cenozoic Eurasia North America Africa 65.5 India South America Madagascar Australia Antarctica Laurasia 135 Mesozoic Gondwana Millions of years ago Pangaea 251 Paleozoic

43. Fig. 25-13a Present Cenozoic North America Eurasia Millions of years ago Africa 65.5 India South America Madagascar Australia Antarctica

44. Fig. 25-13b Laurasia 135 Gondwana Mesozoic Millions of years ago 251 Pangaea Paleozoic

45. The break-up of Pangaea lead to allopatric speciation • The current distribution of fossils reflects the movement of continental drift • For example, the similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached

46. Mass Extinctions • The fossil record shows that most species that have ever lived are now extinct • At times, the rate of extinction has increased dramatically and caused a mass extinction

47. The “Big Five” Mass Extinction Events • In each of the five mass extinction events, more than 50% of Earth’s species became extinct

48. Fig. 25-14 800 20 700 600 15 500 Number of families: 400 Total extinction rate (families per million years): 10 300 200 5 100 0 0 Mesozoic Paleozoic Cenozoic Era Period E C Tr C O S D P J P N 200 145 65.5 0 542 488 444 416 359 299 251 Time (millions of years ago)

49. The Permian extinction defines the boundary between the Paleozoic and Mesozoic eras • This mass extinction occurred in less than 5 million years and caused the extinction of about 96% of marine animal species • This event might have been caused by volcanism, which lead to global warming, and a decrease in oceanic oxygen

50. The Cretaceous mass extinction 65.5 million years ago separates the Mesozoic from the Cenozoic • Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs