1. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. BIOLOGY A GUIDE TO THE NATURAL WORLD FOURTH EDITION DAVID KROGH The Outcomes of Evolution: Macroevolution

2. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 18.1 What is a species?

3. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. What is a Species? The most accepted definition of a species is derived from the biological species concept: “Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.”

4. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. What is a Species? Figure 18.1

5. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. What is a Species? Earth’s organisms are so varied that this definition does not apply to all of them.

6. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 18.2 How Do New Species Arise?

7. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. How Do New Species Arise? Branching evolution occurs when a single “parent” species diverges into two species, the parent species continuing while a second species arises from it. Branching evolution is based on reductions in gene flow between populations of the same species.

8. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. How Do New Species Arise? To the extent that gene flow is maintained between two geographically separate populations, they will experience similar allele frequency changes, meaning they will evolve together.

9. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. How Do New Species Arise? When gene flow is drastically reduced for a long period, however, the populations will evolve separately.

10. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. How Do New Species Arise? When evolution has altered the physical or behavioral characteristics of the populations enough that they will no longer interbreed, even if reunited, speciation has occurred.

11. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Geographical Separation Geographical separation is the most important factor in reducing gene flow between populations of the same species. Such separation can come about because of a change in environment—a river may change course, for example—or because of the migration of part of a population.

12. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Geographical Separation When geographic separation plays a part in the evolution of a species, allopatric speciation is said to have occurred.

13. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Geographical Separation Figure 18.3 The original population started in the north and migrated southward. The population split to the east and west of the Central Valley. Then two populations began to evolve independently. Evolution of eastern population. The east and west populations came back together in Southern California, but could no longer interbreed (or produced infertile hybrid offspring). Evolution of western population. Central Valley

14. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Geographical Separation Geographical separation cannot bring about speciation by itself. Following geographical separation, populations of the same species must develop internal characteristics that will keep them from interbreeding should they be reunited.

15. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Geographical Separation Figure 18.4

16. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Intrinsic Isolating Mechanisms Such characteristics are referred to as intrinsic isolating mechanisms. The six most important mechanisms are: –ecological –temporal –behavioral –mechanical –gametic isolation –hybrid inviability or infertility

17. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Hybrid Inviability or Infertility Figure 18.5

18. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Reproductive Isolating Mechanisms Table 18.1

19. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sympatric Speciation Speciation can occur in the absence of geographical separation, but such sympatric speciation is thought to occur much less frequently than allopatric speciation.

20. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sympatric Speciation The key to sympatric speciation is that populations of a single species need not be separated geographically in order to become reproductively isolated from one another.

21. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Sympatric Speciation Figure 18.6

22. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Speciation and Polyploidy Polyploidy is a special form of sympatric speciation that can give rise to a new species in a single generation.

23. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Speciation and Polyploidy One form of polyploidy is initiated when eggs and sperm from two different species come together to create a hybrid zygote. This zygote doubles its chromosomes, in preparation for cell division, but then fails to divide.

24. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Speciation and Polyploidy The result is an organism whose chromosome set has doubled relative to its starting set.

25. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Speciation and Polyploidy If this organism is able to carry out self- fertilization (as many plants can), then a new species has been formed.

26. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Speciation and Polyploidy Polyploidy is most important in plants, but it has occurred in animal species as well.

27. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Speciation and Polyploidy It speeds the process of evolution by providing a redundancy in alleles that allows some alleles to mutate without causing harm to the organism.

28. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Speciation and Polyploidy PLAY Animation 18.1: Speciation and Polyploidy

29. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 18.3 Many New Species From One: Adaptive Radiation

30. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Adaptive Radiation Speciation is more likely to occur when a species is introduced to an environment in which few other species of its kind exist. Such an environment has many available working roles or niches available to the new species—a situation that leads to rapid specialization, which in turn leads to speciation.

31. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Adaptive Radiation This series of events is known as adaptive radiation: the rapid emergence of many species from a single species that has been introduced to a new environment.

32. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Adaptive Radiation Figure 18.7

33. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 18.4 The Pace of Speciation

34. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Pace of Speciation There is considerable debate among evolutionary biologists regarding the pace of evolution.

35. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Pace of Speciation Figure 18.8 Living organism 1 million years ago 2 million years ago 4 million years ago 17 million years ago

36. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Pace of Speciation Under one view, called the gradualist model, evolution proceeds at a slow, steady rate. Under another view, called the punctuated equilibrium model, organisms undergo long periods of stasis or little change, followed by relatively brief episodes of rapid speciation.

37. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Is Speciation Smooth or Jerky? Figure 18.9 punctuated equilibria According to the gradualism model, speciation occurs through gradual change over long periods of time. According to the punctuated equilibria model, long periods of stasis may periodically be “punctuated” by rapid bursts of speciation.

38. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Is Speciation Smooth or Jerky? Speciation can occur in as little as a few thousand years or as many as several million.

39. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Speedy Speciation Figure 18.10 Amphilophus citrinellusAmphilophus zaliosus

40. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 18.5 The Categorization of Earth’s Living Things

41. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classifying Living Things In science, a two-name or binomial nomenclature is used for each of Earth’s species. The first name designates the genus, or group of closely related organisms, that the species is a member of. The second name is specific to the species.

42. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classifying Living Things Genus and species categories fit into a larger framework of taxonomy, meaning the classification of species.

43. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classifying Living Things From least to most inclusive, the eight most important categories in the taxonomy of Earth’s organisms are species, genus, family, order, class, phylum, kingdom, and domain.

44. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classifying Living Things Figure 18.11 Linnaean System of Classification Kingdom (Animalia) Phylum (Chordata) Class (Mammalia) Order (Carnivora) Family (Felidae) Genus (Felis) Species (Felis domestica)

45. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classifying Living Things Species are put into these categories largely on the basis of relatedness. Species that are closely related are in the same genus while species that are distantly related may only be in the same phylum or kingdom.

46. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classifying Living Things Figure 18.12 ancestral carnivores dogsraccoonsbearssealsweaselswalrus sea lions

47. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Systematics The biological discipline of systematics is concerned with establishing degrees of relatedness among both living and extinct species.

48. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Systematics Systematists establish evolutionary family trees or “phylogenies” by reviewing various kinds of evidence, including radiometric dating, the fossil record, and DNA sequence comparisons. Based on this evidence, they determine the evolutionary relationships among species.

49. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Systematics In practice, most of the work being done in systematics today is molecular work. Scientists compare DNA, RNA, and protein sequences, looking for identifying phylogenetic patterns among them.

50. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Constructing Evolutionary Histories In establishing phylogenies, one of the things systematists look for is homologous structures: common structures in different species that result from a shared ancestry. One problem with the use of these structures is that they can be confused with analogous structures.

51. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Constructing Evolutionary Histories Similar features that developed independently in separate lines of organisms (as with the legs of modern horses and extinct litopterns).

52. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Constructing Evolutionary Histories Figure 18.13 Homology: Common structures in different organisms that result from common ancestry bat bones of wingbones of arm gorilla Analogy: Characters of similar function and superficial structure that have not arisen from common ancestry litoptern one-toed foot horse

53. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 18.6 Classical Taxonomy and Cladistics

54. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classical Taxonomy One method of determining phylogeny, classical taxonomy, establishes evolutionary relationships among living and extinct organisms in accordance with such factors as physical form, distribution, and molecular similarities.

55. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classical Taxonomy and Cladistics But classical taxonomy employs subjective judgments in deciding what weight to give one piece of evidence as opposed to another. The phylogenetic system known as cladistics does away with this element of subjectivity by following a firm rule for inferring relatedness.

56. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Cladistics It counts the number of shared derived characters two organisms have, meaning the features they uniquely share that are derived from another group of organisms.

57. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Cladistics Cladistics is centrally concerned with establishing lines of descent, although species can be put into taxonomic categories that are derived from cladistic analysis.

58. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. A Simple Cladogram Figure 18.14 hagfishlizarddeerlion Derived characters tetrapod structure mammary glands carnivorous feeding aquatic habitat seal

59. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classical Taxonomy and Cladistics Classical taxonomy holds that, in putting organisms into various categories, factors other than phylogeny ought to be taken into account. Cladistics holds that the only criterion for taxonomic placement is phylogeny—a group must contain all descendants stemming from a given branch point in a family tree.

60. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Classical Taxonomy and Cladistics Figure 18.15 Classical view of relationships among tetrapods ReptiliaAvesMammalia Cladistic view of relationships among tetrapods turtles snakeslizardscrocodiles dinosaurs birdsmammalsturtles snakes lizardscrocodilesbirdsmammals dinosaurs