24 Lectures Ppt
- 1. Chapter 24 The Origin of Species
- 2. Overview: The “Mystery of Mysteries” In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth Video: Galápagos Tortoise
- 4. 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
- 5. Two basic patterns of evolutionary change: Anagenesis (phyletic evolution) transforms one species into another Cladogenesis (branching evolution) is the splitting of a gene pool, giving rise to one or more new species Animation: Macroevolution
- 6. LE 24-2 Anagenesis Cladogenesis
- 7. Concept 24.1: The biological species concept emphasizes reproductive isolation Species is a Latin word meaning “kind” or “appearance”
- 8. The Biological Species Concept Members of a biological species are reproductively compatible, at least potentially; they cannot interbreed with other populations.
- 9. LE 24-3 Similarity between different species. Diversity within a species.
- 10. Reproductive Isolation Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile hybrids Two types of barriers: prezygotic and postzygotic
- 11. Prezygotic barriers impede mating or hinder fertilization if mating does occur: Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation
- 12. Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
- 13. LE 24-4a Prezygotic barriers impede mating or hinder fertilization if mating does occur Postzygotic barriers prevent a hybrid zygote from developing into a viable, fertile adult REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION GAMETIC ISOLATION Reduced hybrid viability Fertilization Viable, fertile offspring Reduced hybrid fertility Hybrid breakdown Mating attempt Gametic isolation Fertilization Mechanical isolation Behavioral isolation Temporal isolation Habitat isolation Individuals of different species
- 14. Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes
- 17. Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers
- 19. Mechanical isolation: Morphological differences can prevent successful mating
- 21. Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species Video: Blue-footed Boobies Courtship Ritual Video: Giraffe Courtship Ritual Video: Albatross Courtship Ritual
- 23. LE 24-4aa Prezygotic barriers impede mating or hinder fertilization if mating does occur HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION GAMETIC ISOLATION Mating attempt Gametic isolation Fertilization Mechanical isolation Behavioral isolation Temporal isolation Habitat isolation Individuals of different species
- 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
- 27. Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile
- 29. 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
- 31. LE 24-4ab Postzygotic barriers prevent a hybrid zygote from developing into a viable, fertile adult REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN Reduced hybrid viability Fertilization Viable, fertile offspring Reduced hybrid fertility Hybrid breakdown
- 32. Limitations of the Biological Species Concept The biological species concept does not apply to Asexual organisms Fossils Organisms about which little is known regarding their reproduction
- 33. Other Definitions of Species Morphological: defines a species by structural features Paleontological: focuses on morphologically discrete species known only from the fossil record Ecological: views a species in terms of its ecological niche Phylogenetic: defines a species as a set of organisms with a unique genetic history
- 34. Concept 24.2: Speciation can take place with or without geographic separation Speciation can occur in two ways: Allopatric speciation Sympatric speciation
- 35. LE 24-5 Allopatric speciation Sympatric speciation
- 36. Allopatric (“Other Country”) Speciation In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations One or both populations may undergo evolutionary change during the period of separation
- 37. LE 24-6 A. harrisi A. leucurus
- 38. To determine if allopatric speciation has occurred, reproductive isolation must have been established
- 39. LE 24-7a Initial population of fruit flies (Drosophila pseudoobscura) Mating experiments after several generations Some flies raised on maltose medium Some flies raised on starch medium
- 40. LE 24-7b Female Female Starch Maltose Starch Maltose Male Same population Different populations Male 20 8 Mating frequencies in experimental group Mating frequencies in control group 18 15 15 12 Same population Different populations 9 22
- 41. Sympatric (“Same Country”) Speciation In sympatric speciation, speciation takes place in geographically overlapping populations
- 42. Polyploidy Polyploidy is presence of extra sets of chromosomes due to accidents during cell division It has caused the evolution of some plant species An autopolyploid is an individual with more than two chromosome sets, derived from one species
- 43. LE 24-8 Failure of cell division in a cell of a growing diploid plant after chromosome duplication gives rise to a tetraploid branch or other tissue. Gametes produced by flowers on this tetraploid branch are diploid. Offspring with tetraploid karyo- types may be viable and fertile—a new biological species. 2 n = 6 4 n = 12 4 n 2 n
- 44. An allopolyploid is a species with multiple sets of chromosomes derived from different species
- 45. LE 24-9 Species B 2 n = 6 Species A 2 n = 4 Normal gamete n = 3 Normal gamete n = 3 2 n = 10 Unreduced gamete with 4 chromosomes Unreduced gamete with 7 chromosomes Hybrid with 7 chromosomes Viable fertile hybrid (allopolyploid) Meiotic error; chromosome number not reduced from 2 n to n
- 46. Habitat Differentiation and Sexual Selection Sympatric speciation can also result from the appearance of new ecological niches In cichlid fish, sympatric speciation has resulted from nonrandom mating due to sexual selection
- 47. LE 24-10 Normal light Monochromatic orange light P. pundamilia P. nyererei
- 48. Allopatric and Sympatric Speciation: A Summary In allopatric speciation, a new species forms while geographically isolated from its parent population In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species
- 49. Adaptive Radiation Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities
- 51. The Hawaiian archipelago is one of the world’s great showcases of adaptive radiation
- 52. LE 24-12 KAUAI 5.1 million years OAHU 3.7 million years HAWAII 0.4 million years 1.3 million years MAUI MOLOKAI LANAI Argyroxiphium sandwicense Dubautia linearis Dubautia scabra Dubautia waialealae Dubautia laxa N
- 53. Studying the Genetics of Speciation The explosion of genomics is enabling researchers to identify specific genes involved in some cases of speciation
- 54. The Tempo of Speciation The fossil record includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then apparently disappear Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence
- 55. LE 24-13 Time Gradualism model Punctuated equilibrium model
- 56. Concept 24.3: Macroevolutionary changes can accumulate through many speciation events Macroevolutionary change is cumulative change during thousands of small speciation episodes
- 57. Evolutionary Novelties Most novel biological structures evolve in many stages from previously existing structures
- 58. Some complex structures, such as the eye, have had similar functions during all stages of their evolution
- 59. LE 24-14 Complex camera-type eye Pinhole camera-type eye Eye with primitive lens Patch of pigmented cells Eyecup Pigmented cells (photoreceptors) Epithelium Nerve fibers Fluid-filled cavity Epithelium Pigmented layer (retina) Optic nerve Pigmented cells Nerve fibers Cornea Cellular fluid (lens) Optic nerve Cornea Lens Optic nerve Retina
- 60. Evolution of the Genes That Control Development Genes that program development control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult
- 61. Changes in Rate and Timing Heterochrony is an evolutionary change in the rate or timing of developmental events It can have a significant impact on body shape Allometric growth is the proportioning that helps give a body its specific form Animation: Allometric Growth
- 62. LE 24-15a Differential growth rates in a human Newborn Age (years) Adult 2 5 15
- 63. Different allometric patterns contribute to the contrasting shapes of human and chimpanzee skulls
- 64. LE 24-15b Chimpanzee fetus Chimpanzee adult Human fetus Human adult Comparison of chimpanzee and human skull growth
- 65. Heterochrony has also played a part in the evolution of salamander feet
- 66. LE 24-16 Ground-dwelling salamander Tree-dwelling salamander
- 67. In paedomorphosis, the rate of reproductive development accelerates compared with somatic development The sexually mature species may retain body features that were juvenile structures in an ancestral species
- 69. Changes in Spatial Pattern Substantial evolutionary change can also result from alterations in genes that control the placement and organization of body parts Homeotic genes determine such basic features as where wings and legs will develop on a bird or how a flower’s parts are arranged
- 70. The products of one class of homeotic genes called Hox genes Hox genes provide positional information in the development of fins in fish and limbs in tetrapods
- 71. LE 24-18 Chicken leg bud Region of Hox gene expression Zebrafish fin bud
- 72. Evolution of vertebrates from invertebrate animals was associated with alterations in Hox genes
- 73. LE 24-19 Hypothetical vertebrate ancestor (invertebrate) with a single Hox cluster First Hox duplication Hypothetical early vertebrates (jawless) with two Hox clusters Second Hox duplication Vertebrates (with jaws) with four Hox clusters
- 74. Evolution Is Not Goal Oriented The fossil record often shows apparent trends in evolution that may arise because of adaptation to a changing environment
- 75. LE 24-20 Pleistocene Sinohippus Recent Pliocene Anchitherium Miocene Paleotherium Oligocene Propalaeotherium Eocene Pachynolophus Hyracotherium Mesohippus Miohippus Orohippus Epihippus Key Grazers Browsers Hypohippus Parahippus Archaeohippus Merychippus Callippus Megahippus Pliohippus Nannippus Hipparion Neohipparion Hippidion and other genera Equus
- 76. According to the species selection model, trends may result when species with certain characteristics endure longer and speciate more often than those with other characteristics The appearance of an evolutionary trend does not imply that there is some intrinsic drive toward a particular phenotype