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Many species of cormorants around the world can fly. Cormorants on the Gal pagos Islands cannot fly. How did these fligh

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Many species of cormorants around the world can fly. Cormorants on the Gal pagos Islands cannot fly. How did these fligh

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    1. Many species of cormorants around the world can fly. Cormorants on the Galápagos Islands cannot fly. How did these flightless cormorants get to the Galápagos Islands? Why are these flightless cormorants found nowhere else in the world? Chapter 14 The Origin of Species

    2. Figure 14.02 Flightless cormorant Figure 14.0_2 Flightless cormorantFigure 14.0_2 Flightless cormorant

    3. An ancestral cormorant species is thought to have flown from the Americas to the Galápagos Islands more than 3 million years ago. Terrestrial mammals could not make the trip over the wide distance, and no predatory mammals naturally occur on these islands today. Without predators, the environment of these cormorants favored birds with smaller wings, perhaps channeling resources to the production of offspring. Introduction

    4. DEFINING SPECIES

    5. 14.1 The origin of species is the source of biological diversity Microevolution is the change in the gene pool of a population from one generation to the next. Speciation is the process by which one species splits into two or more species. Every time speciation occurs, the diversity of life increases. The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.5 billion years ago.

    6. 14.2 There are several ways to define a species The word species is from the Latin for “kind” or “appearance.” Although the basic idea of species as distinct life-forms seems intuitive, devising a more formal definition is not easy and raises questions. How similar are members of the same species? What keeps one species distinct from others?

    7. The biological species concept defines a species as a group of populations, whose members have the potential to interbreed in nature, and produce fertile offspring. Therefore, members of a species are similar because they reproduce with each other. 14.2 There are several ways to define a species

    8. Reproductive isolation prevents members of different species from mating with each other, prevents gene flow between species, and maintains separate species. Therefore, species are distinct from each other because they do not share the same gene pool. 14.2 There are several ways to define a species

    9. Figure 14.2A Similarity between two species: the eastern meadowlark (left) and western meadowlark (right). Similar looking but different songs and mating behavior Figure 14.2A Similarity between two species: the eastern meadowlark (left) and western meadowlark (right)Figure 14.2A Similarity between two species: the eastern meadowlark (left) and western meadowlark (right)

    10. Figure 14.2B Diversity within one species Figure 14.2B Diversity within one species Figure 14.2B Diversity within one species

    11. The biological species concept can be problematic. Some pairs of clearly distinct species occasionally interbreed and produce hybrids. For example, grizzly bears and polar bears may interbreed and produce hybrids called grolar bears. Melting sea ice may bring these two bear species together more frequently and produce more hybrids in the wild. Reproductive isolation cannot usually be determined for extinct organisms known only from fossils. Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually. Therefore, alternate species concepts can be useful. 14.2 There are several ways to define a species

    12. Figure 14.2C Hybridization between two species of bears Figure 14.2C Hybridization between two species of bearsFigure 14.2C Hybridization between two species of bears

    13. The morphological species concept classifies organisms based on observable physical traits and can be applied to asexual organisms and fossils. However, there is some subjectivity in deciding which traits to use. 14.2 There are several ways to define a species

    14. The ecological species concept defines a species by its ecological role or niche and focuses on unique adaptations to particular roles in a biological community. For example, two species may be similar in appearance but distinguishable based on what they eat or where they live. 14.2 There are several ways to define a species

    15. The phylogenetic species concept defines a species as the smallest group of individuals that shares a common ancestor and thus forms one branch of the tree of life. Biologists trace the phylogenetic history of a species by comparing its morphology or DNA. However, defining the amount of difference required to distinguish separate species is a problem. 14.2 There are several ways to define a species

    16. 14.3 Reproductive barriers keep species separate Reproductive barriers serve to isolate the gene pools of species and prevent interbreeding. Depending on whether they function before or after zygotes form, reproductive barriers are categorized as prezygotic or postzygotic.

    17. Figure 14.3A Figure 14.3A Reproductive barriers between speciesFigure 14.3A Reproductive barriers between species

    18. Five types of prezygotic barriers prevent mating or fertilization between species. In habitat isolation, two species live in the same general area but not in the same kind of place. In temporal isolation, two species breed at different times (seasons, times of day, years). 14.3 Reproductive barriers keep species separate

    19. Figure 14.3B Habitat isolation in two species of garter snakes, one that is terrestrial, the other aquatic Figure 14.3B Habitat isolationFigure 14.3B Habitat isolation

    20. Figure 14.3C Temporal isolation between Eastern and Western Spotted skunks that breed at different times of the year Figure 14.3C Temporal isolationFigure 14.3C Temporal isolation

    21. Prezygotic Barriers, continued In behavioral isolation, there is little or no mate recognition between females and males of different species. In mechanical isolation, female and male sex organs are not compatible. In gametic isolation, female and male gametes are not compatible. 14.3 Reproductive barriers keep species separate

    22. Figure 14.3D Behavioral Isolation in mating dance of blue-footed boobies Figure 14.3D Behavioral IsolationFigure 14.3D Behavioral Isolation

    23. Figure 14.3E Mechanical isolation shown by spirals of two different snail species causing genital openings (arrows) to not align Figure 14.3E Mechanical isolationFigure 14.3E Mechanical isolation

    24. Figure 14.3F Gametic isolation in red and purple sea urchins as gametes cannot fuse because cell surface proteins do not match Figure 14.3F Gametic isolationFigure 14.3F Gametic isolation

    25. Three types of postzygotic barriers operate after hybrid zygotes have formed. In reduced hybrid viability, most hybrid offspring do not survive. In reduced hybrid fertility, hybrid offspring are vigorous but sterile. In hybrid breakdown, the first-generation hybrids are viable and fertile but the offspring of the hybrids are feeble or sterile. 14.3 Reproductive barriers keep species separate

    26. Figure 14.3G Reduced hybrid fertility in mules Figure 14.3G Reduced hybrid fertilityFigure 14.3G Reduced hybrid fertility

    27. MECHANISMS OF SPECIATION

    28. 14.4 In allopatric speciation, geographic isolation leads to speciation In allopatric speciation, populations of the same species are geographically separated, isolating their gene pools. Isolated populations will no longer share changes in allele frequencies caused by natural selection, genetic drift, and/or mutation.

    29. Gene flow between populations is initially prevented by a geographic barrier. For example the Grand Canyon and Colorado River separate two species of antelope squirrels, and the Isthmus of Panama separates 15 pairs of snapping shrimp. 14.4 In allopatric speciation, geographic isolation leads to speciation

    30. Figure 14.4A Allopatric speciation of geographically isolated antelope squirrels (Ammospermophilus) Figure 14.4A Allopatric speciation of geographically isolated antelope squirrelsFigure 14.4A Allopatric speciation of geographically isolated antelope squirrels

    31. Figure 14.4B Allopatric speciation in snapping shrimp Figure 14.4B Allopatric speciation in snapping shrimpFigure 14.4B Allopatric speciation in snapping shrimp

    32. 14.5 Reproductive barriers can evolve as populations diverge How do reproductive barriers arise? Experiments have demonstrated that reproductive barriers can evolve as a by-product of changes in populations as they adapt to different environments. These studies have included laboratory studies of fruit flies and field studies of monkey flowers and their pollinators.

    33. Figure 14.5A Evolution of reproductive barriers in laboratory populations of fruit flies adapted to different food sources Figure 14.5A Evolution of reproductive barriers in laboratory populations of fruit flies adapted to different food sourcesFigure 14.5A Evolution of reproductive barriers in laboratory populations of fruit flies adapted to different food sources

    34. Figure 14.5B Transferring an allele between monkey flowers changes flower color and influences pollinator choice. Figure 14.5B Transferring an allele between monkey flowers changes flower color and influences pollinator choice.Figure 14.5B Transferring an allele between monkey flowers changes flower color and influences pollinator choice.

    35. 14.6 Sympatric speciation takes place without geographic isolation Sympatric speciation occurs when a new species arises within the same geographic area as a parent species. How can reproductive isolation develop when members of sympatric populations remain in contact with each other? Gene flow between populations may be reduced by polyploidy, habitat differentiation, or sexual selection.

    36. Many plant species have evolved by polyploidy in which cells have more than two complete sets of chromosomes. Sympatric speciation can result from polyploidy within a species (by self-fertilization) or between two species (by hybridization). 14.6 Sympatric speciation takes place without geographic isolation ..

    37. Figure 14.6A Sympatric speciation by polyploidy within a single species Figure 14.6A_s3 Sympatric speciation by polyploidy within a single species (step 3) Figure 14.6A_s3 Sympatric speciation by polyploidy within a single species (step 3)

    38. Figure 14.6B Sympatric speciation producing a hybrid polyploid from two different species Figure 14.6B_s3 Sympatric speciation producing a hybrid polyploid from two different species (step 3) Figure 14.6B_s3 Sympatric speciation producing a hybrid polyploid from two different species (step 3)

    39. 14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation Plant biologists estimate that 80% of all living plant species are descendants of ancestors that formed by polyploid speciation. Hybridization between two species accounts for most of these species.

    40. 14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation Polyploid plants include cotton, oats, potatoes, bananas, peanuts, barley,

    41. Wheat has been domesticated for at least 10,000 years and is the most widely cultivated plant in the world. Bread wheat, Triticum aestivum, is a polyploid with 42 chromosomes and the result of hybridization and polyploidy. 14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation

    42. Figure 14.7 The evolution of bread wheat, Triticum aestivum Figure 14.7 The evolution of bread wheat, Triticum aestivumFigure 14.7 The evolution of bread wheat, Triticum aestivum

    43. 14.8 Isolated islands are often showcases of speciation Most of the species on Earth are thought to have originated by allopatric speciation. Isolated island chains offer some of the best evidence of this type of speciation. Multiple speciation events are more likely to occur in island chains that have physically diverse habitats, islands far enough apart to permit populations to evolve in isolation, and islands close enough to each other to allow occasional dispersions between them.

    44. 14.8 Isolated islands are often showcases of speciation The evolution of many diverse species from a common ancestor is adaptive radiation. The Galápagos Archipelago is located about 900 km (560 miles) west of Ecuador, is one of the world’s great showcases of adaptive radiation, was formed naked from underwater volcanoes, was colonized gradually from other islands and the South America mainland, and has many species of plants and animals found nowhere else in the world.

    45. 14.8 Isolated islands are often showcases of speciation The Galápagos islands currently have 14 species of closely related finches, called Darwin’s finches, because Darwin collected them during his around-the-world voyage on the Beagle. These finches share many finchlike traits, differ in their feeding habits and their beaks, specialized for what they eat, and arose through adaptive radiation.

    46. Figure 14.8 Figure 14.8 Examples of differences in beak shape and size in Galápagos finches, each adapted for a specific dietFigure 14.8 Examples of differences in beak shape and size in Galápagos finches, each adapted for a specific diet

    47. Peter and Rosemary Grant have worked for more than three decades, on medium ground finches, and on tiny, isolated, uninhabited Daphne Major in the Galápagos Islands. 14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches

    48. Medium ground finches and cactus finches occasionally interbreed. Hybrids have intermediate bill sizes, survive well during wet years, when there are plenty of soft, small seeds around, are outcompeted by both parental types during dry years, and can introduce more genetic variation on which natural selection acts. 14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches

    49. Figure 14.9 Changes in mean beak size in the medium ground finch (G. fortis) Figure 14.9 Changes in mean beak size in the medium ground finch (G. fortis)Figure 14.9 Changes in mean beak size in the medium ground finch (G. fortis)

    50. 14.10 Hybrid zones provide opportunities to study reproductive isolation What happens when separated populations of closely related species come back into contact with each other? Biologists try to answer such questions by studying hybrid zones, regions in which members of different species meet and mate to produce at least some hybrid offspring.

    51. 14.10 Hybrid zones provide opportunities to study reproductive isolation Over time in hybrid zones (Fig 14.10A) reinforcement may strengthen barriers to reproduction, such as occurs in flycatchers (Fig. 14.10B), or fusion may reverse the speciation process as gene flow between species increases, as may be occurring among the cichlid species in Lake Victoria (Fig. 14.10C). In stable hybrid zones, a limited number of hybrid offspring continue to be produced.

    52. Figure 14.10A Formation of a hybrid zone Figure 14.10A Formation of a hybrid zoneFigure 14.10A Formation of a hybrid zone

    53. Figure 14.10B Reinforcement of reproductive barriers Figure 14.10B Reinforcement of reproductive barriersFigure 14.10B Reinforcement of reproductive barriers

    54. Figure 14.10C Fusion: males of Pundamilia nyererei and Pundamilia pundamilia contrasted with a hybrid from an area with turbid water Figure 14.10C Fusion: males of Pundamilia nyererei and Pundamilia pundamilia contrasted with a hybrid from an area with turbid waterFigure 14.10C Fusion: males of Pundamilia nyererei and Pundamilia pundamilia contrasted with a hybrid from an area with turbid water

    55. 14.11 Speciation can occur rapidly or slowly There are two models for the tempo of speciation. The punctuated equilibria model draws on the fossil record, where species change most as they arise from an ancestral species and then experience relatively little change for the rest of their existence. Other species appear to have evolved more gradually = gradualism.

    56. Figure 14.11 Two models for the tempo of speciation Figure 14.11 Two models for the tempo of speciationFigure 14.11 Two models for the tempo of speciation

    57. 14.11 Speciation can occur rapidly or slowly What is the total length of time between speciation events (between formation of a species and subsequent divergence of that species)? In a survey of 84 groups of plants and animals, the time ranged from 4,000 to 40 million years. Overall, the time between speciation events averaged 6.5 million years.

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