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  • 1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsPowerPoint Lectures forBiology, Seventh EditionNeil Campbell and Jane ReeceLectures by Chris RomeroChapter 24The Origin of Species
  • 2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsOverview: The “Mystery of Mysteries”• In the Galápagos Islands Darwin discoveredplants and animals found nowhere else on Earth
  • 3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Speciation, the origin of new species, is at thefocal point of evolutionary theory• Evolutionary theory must explain how new speciesoriginate and how populations evolve• Microevolution consists of adaptations that evolvewithin a population, confined to one gene pool• Macroevolution refers to evolutionary changeabove the species level
  • 5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe biological species concept emphasizesreproductive isolation• Species is a Latin word meaning “kind” or“appearance”
  • 6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe Biological Species Concept• Members of a biological species arereproductively compatible, at least potentially; theycannot interbreed with other populations.
  • 7. LE 24-3Similarity between different species.Diversity within a species.
  • 8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsReproductive Isolation• Reproductive isolation is the existence ofbiological factors (barriers) that impede twospecies from producing viable, fertile hybrids• Two types of barriers: prezygotic and postzygotic
  • 9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Prezygotic barriers impede mating or hinderfertilization if mating does occur:– Habitat isolation– Temporal isolation– Behavioral isolation– Mechanical isolation– Gametic isolation
  • 10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Habitat isolation: Two species encounter eachother rarely, or not at all, because they occupydifferent habitats, even though not isolated byphysical barriers
  • 11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Temporal isolation: Species that breed at differenttimes of the day, different seasons, or differentyears cannot mix their gametes
  • 12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Behavioral isolation: Courtship rituals and otherbehaviors unique to a species are effectivebarriers
  • 15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Mechanical isolation: Morphological differencescan prevent successful mating
  • 17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Gametic isolation: Sperm of one species may notbe able to fertilize eggs of another species
  • 19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Postzygotic barriers prevent the hybrid zygotefrom developing into a viable, fertile adult:– Reduced hybrid viability– Reduced hybrid fertility– Hybrid breakdown
  • 21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Reduced hybrid viability: Genes of the differentparent species may interact and impair thehybrid’s development
  • 22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Reduced hybrid fertility: Even if hybrids arevigorous, they may be sterile
  • 24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Hybrid breakdown: Some first-generation hybridsare fertile, but when they mate with anotherspecies or with either parent species, offspring ofthe next generation are feeble or sterile
  • 26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsLimitations of the Biological Species Concept• The biological species concept does not apply to– Asexual organisms– Fossils– Organisms about which little is knownregarding their reproduction
  • 28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsOther Definitions of Species• Morphological: defines a species by structuralfeatures• Paleontological: focuses on morphologicallydiscrete species known only from the fossil record• Ecological: views a species in terms of itsecological niche• Phylogenetic: defines a species as a set oforganisms with a unique genetic history
  • 29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsSpeciation can take place with or withoutgeographic separation• Speciation can occur in two ways:– Allopatric speciation– Sympatric speciation
  • 30. LE 24-5Allopatric speciation Sympatric speciation
  • 31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsAllopatric (“Other Country”) Speciation• In allopatric speciation, gene flow is interrupted orreduced when a population is divided intogeographically isolated subpopulations• One or both populations may undergoevolutionary change during the period ofseparation
  • 32. LE 24-6A. harrisi A. leucurus
  • 33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• To determine if allopatric speciation has occurred,reproductive isolation must have been established
  • 34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsSympatric (“Same Country”) Speciation• In sympatric speciation, speciation takes place ingeographically overlapping populations
  • 35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsPolyploidy• Polyploidy is presence of extra sets ofchromosomes due to accidents during cell division• It has caused the evolution of many plant species• An autopolyploid is an individual with more thantwo chromosome sets, derived from one species
  • 36. LE 24-8Failure of cell divisionin a cell of a growingdiploid plant afterchromosome duplicationgives rise to a tetraploidbranch or other tissue.Gametes producedby flowers on thistetraploid branchare diploid.Offspring withtetraploid karyo-types may beviable and fertile—a new biologicalspecies.2n = 64n = 12 4n2n
  • 37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsHabitat Differentiation and Sexual Selection• Sympatric speciation can also result from theappearance of new ecological niches• In cichlid fish, sympatric speciation has resultedfrom nonrandom mating due to sexual selection
  • 38. LE 24-10Normal light Monochromatic orange lightP. pundamiliaP. nyererei
  • 39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsAllopatric and Sympatric Speciation: A Summary• In allopatric speciation, a new species forms whilegeographically isolated from its parent population• In sympatric speciation, a reproductive barrierisolates a subset of a population withoutgeographic separation from the parent species
  • 40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsAdaptive Radiation• Adaptive radiation is the evolution of diverselyadapted species from a common ancestor uponintroduction to new environmental opportunities
  • 41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • 42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• The Hawaiian archipelago is one of the world’sgreat showcases of adaptive radiation
  • 43. LE 24-12KAUAI5.1millionyears OAHU3.7millionyearsHAWAII0.4millionyears1.3millionyearsMAUIMOLOKAILANAI Argyroxiphium sandwicenseDubautia linearisDubautia scabraDubautia waialealaeDubautia laxaN
  • 44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsStudying the Genetics of Speciation• The explosion of genomics is enablingresearchers to identify specific genes involved insome cases of speciation
  • 45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe Tempo of Speciation• The fossil record includes many episodes in whichnew species appear suddenly in a geologicstratum, persist essentially unchanged throughseveral strata, and then apparently disappear• Niles Eldredge and Stephen Jay Gould coined theterm punctuated equilibrium to describe periods ofapparent stasis punctuated by sudden change• The punctuated equilibrium model contrasts with amodel of gradual change in a species’ existence
  • 46. LE 24-13TimeGradualism model Punctuated equilibrium model
  • 47. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsMacroevolutionary changes can accumulatethrough many speciation events• Macroevolutionary change is cumulative changeduring thousands of small speciation episodes
  • 48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsEvolutionary Novelties• Most novel biological structures evolve in manystages from previously existing structures
  • 49. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Some complex structures, such as the eye, havehad similar functions during all stages of theirevolution
  • 50. LE 24-14Complex camera-type eyePinhole camera-type eye Eye with primitive lensPatch of pigmented cells EyecupPigmented cells(photoreceptors)EpitheliumNerve fibersFluid-filled cavityEpitheliumPigmentedlayer (retina)OpticnervePigmentedcellsNerve fibersCorneaCellularfluid(lens)Optic nerveCorneaLensOptic nerveRetina
  • 51. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsEvolution Is Not Goal Oriented• The fossil record often shows apparent trends inevolution that may arise because of adaptation toa changing environment
  • 52. LE 24-20PleistoceneSinohippusRecentPlioceneAnchitheriumMiocenePaleotheriumOligocenePropalaeotheriumEocene PachynolophusHyracotheriumMesohippusMiohippusOrohippusEpihippusKeyGrazersBrowsersHypohippusParahippusArchaeohippusMerychippusCallippusMegahippusPliohippusNannippusHipparion NeohipparionHippidion and other generaEquus
  • 53. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• According to the species selection model, trendsmay result when species with certaincharacteristics endure longer and speciate moreoften than those with other characteristics• The appearance of an evolutionary trend does notimply that there is some intrinsic drive toward aparticular phenotype