The Origin of Species chapter 24 - PowerPoint Presentation

1. The Origin of Specieschapter 24Campbell and Reece

2. Speciationprocess by which one species splits into 2 or more speciesSpeciation explains both the diversity of life and the unity of living things.

3. Speciation : forms bridge between:MICROEVOLUTIONEvolutionary change below species levelExample:change in allele frequencies in population over generationsMACROEVOLUTIONEvolutionary change above the species levelExamples:origin of new group of organismsimpact of mass extinctions

4. Biological Species ConceptSpecies: a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspringmembers of a species cannot produce viable, fertile offspring with other groupsemphasizes the separateness of species due to reproductive barriers

5. What holds the gene pool of a species together?Gene Flow: transfer of alleles between populations of same speciesexchange of alleles tends to hold populations together genetically

6. Reproductive Isolationexistence of biological barriers that keep members of 2 populations from interbreeding over long periods of time

7. Reproductive Isolationblock gene flow between the species & limit formation of hybrids

8. Reproductive Isolationhybrids: offspring that result from the mating of individuals from 2 different species or from 2 true-breeding varieties of same species

9. Reproductive Isolationsingle barrier may not prevent all gene flowcombination of several barriers can effectively isolate a species’ gene pool2 categories:prezygotic barrierspostzygotic barriers

10. Prezygotic Barriersblock fertilization from happening by:impeding members of different species from attempting to matepreventing attempted mating from being completed successfullyhindering fertilization if mating was completed successfully

11. Postzygotic Barriersreproductive barrier that prevents hybrid zygotes produced by 2 different species from developing into viable, fertile adultslethal developmental errorsinfertility in viable offspring

12. Types of Prezygotic Reproductive BarriersHabitat Isolation2 species that occupy different habitats w/in same area may rarely interactexample:

13. Types of Prezygotic Reproductive Barriers2. Temporal Isolation:species breed during different times of day, different seasons, or different yearseastern & western spotted skunks: 1 breeds in late summer other in late winter

14. Types of Prezygotic Reproductive Barriers3. Behavioral Isolation:courtship rituals used to attract mates are effective barriers

15. Types of Prezygotic Reproductive Barriers4. Mechanical Isolation:morphological differences prevent successful completion even if attempted

16. Types of Prezygotic Reproductive Barriers5. Gametic Isolation:sperm of 1 species may not be able to fertilize egg of another:reproductive tract hostile to spermsperm does not have enzymes to penetrate zona pellicida of another species

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19. Types of Postzygotic Reproductive BarriersReduced Hybrid Viability:hybrids development or survival is impaired

20. Types of Postzygotic Reproductive Barriers2. Reduced Hybrid Fertility:hybrids may develop and be healthy but they are not fertile

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22. Types of Postzygotic Reproductive BarriersHybrid Breakdown:Some 1st generation hybrids are fertile but those offspring are feeble or sterile

23. Species There is no single, universally applicable species concept that can define, explain, and identify all species.There are multiple ways to think about & define species.

24. Biological Species Limitationsunable to use these characteristics on fossils of extinct speciesonly applies to organisms that reproduce sexuallyonly applies where there is no gene flow

25. Other Definitions of Speciesthese dfns emphasize the unity w/in a species.morphological species concept: characterizes a species by a structural featureapplies to species that reproduce sexually or asexuallyhow scientists distinguish most speciesdisadvantage: subjective

26. Morphological Species ConceptProblems:domestic dogs may look very different but are still same speciesmouse lemurs look very similar but there are 18 species of themgrey mouse lemur lesser mouse lemur

27. Ecological Species Conceptviews species in terms of its nichethe sum of how members of the species interact with the nonliving & living parts of their environmentasexual or sexual speciesemphasizes role of disruptive NS as organisms adapt to different environmental conditions

28. Phylogenetic Species Conceptdefines species as smallest group of individuals that share a common ancestor, forming one branch on the “tree of life”determining degree of differences is difficult

29. SpeciesThere are >20 other ways to define species

30. Speciation can take place with or w/out geographic separationSpeciation can occur in 2 main ways:Allopatric SpeciationSympatric Speciation

31. ALLOPATRIC SPECIATION“other country”gene flow is interrupted when population is divided into geographically isolated subpopulations

32. Allopatric Speciation Processonce geographic separation has occurred, the separated gene pools will each have their own mutationsNS & genetic drift may alter allele frequencies in different ways in each subpopulation group

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34. Allopatric Speciation

35. Evidence of Allopatric Speciationare many studies & examples supporting this type speciationindirect support: regions that are isolated or highly subdivided have more species than regions w/out those features

36. Drosophila Experiment

37. Sympatric Speciation“same country”occurs in populations in same geographic arealess common than allopatric occurs if gene flow is reduced by factors like:polyploidyhabitat differentiationsexual selection

38. POLYPLOIDYmeans extra sets of chromosomescan occur in animalsgray tree frog (Hyla versicolor)around Great Lakes

39. Polyploidymuch more common in plantsestimate: 80% of today’s plants species have ancestors that formed by polyploid speciation2 forms

40. 1. Autopolyploidindividual has >2 chromosome sets all derived from a single speciesplant polyploidy

41. Plant Polyploidytetraploid plant can produce fertile tetraploid offspring by self-pollinating or mating with other tetraploids

42. 2. Allopolyploid2 different species interbreed making a hybridhybrid reproduces asexuallyover generations sterile hybrid  fertile polyploid (called an allopolyploid)

43. Allopolyploids can breed with each other but not with either of their parents so are a new speciesrare: 5 new plant species since 1850 documentedMimulus peregrinus

44. Allopolyploids include many agricultural cropsTriticum aestivum (bread wheat) has 6 sets chromosomes (2 pair from each of 3 parents), an allohexaploid1st polyploidy event probably occurred ~8,000 yrs ago as spontaneous hybrid

45. Top 2 parentsbottom: Triticum aestivum

46. Allopolyploids plant geneticists “create” new polyploids making hybrids with desired characteristicsuse chemicals that induce meiotic & mitotic errors

47. Habitat DifferentiationSympatric speciation can occur when genetic factors enable a subpopulation to exploit a habitat or resource used by the parent population

48. Rhagoletis pomonellaNorth American apple maggot flyoriginal habitat was the native hawthorn tree

49. Habitat Differentiation apples mature faster than hawthorn fruit, NS has favored flies with rapid developmenthave an allele that benefits flies that feed off only 1 or the other not both (post-zygotic barrier to reproduction)flies feeding on apple trees now show temporal isolation from flies still eating hawthorn fruit (prezygotic restriction to gene flow)

50. Sexual Selectioncan also drive sympatric speciation:cichlid fish Pundamilia pundamilia

51. Cichlid Fish>600 species found in Lake Victoriaoriginated in past 100 000 yrshypothesis : subgroups of original population adapted to different food sources  genetic divergencefemale preference for mates may also be a factor: 1 species breeding males have blue back another species has orange back

52. Breeding Cichlids Colors

53. Sexual Selection Studyplaced the 2 subspecies in same tank used monochromatic orange light so both appeared very similarfemales bred with eitherconclusion: mate choice by females is based on male coloration so it’s the main reproductive barrier (prezygotic behavior)

54. Allopatric & Sympatric Speciation are the 2 main modes of speciationAllopatricgeographic isolationNSgenetic driftsexual selectionSympatricrequires emergence of a reproductive barrier that isolates a subgroupless commonpolyploidysexual selection

55. Hybrid ZonesA region in which members of different species meet & mate, producing at least some offspring of mixed ancestry.Hybrids are more likely to die as embryos & show a variety of morphological abnormalities

56. Hybrids of yellow-bellied & fire-bellied toadsBombino bambino Bombino variegataHybrids are more likely to die as embryos & show a variety of morphological abnormalities

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58. Hybrid Zones

59. Hybrid Zones over Timebarriers between parent species may increase (strengthening of reproductive barriers)eventually hybrids no longer formed

60. Hybrid Zones over TimeOr barrier weakens 2 species fuse

61. Hybrid Zone over Time3rd possibility:status quo is stabilized and hybrids continue to be produced

62. Speciation Time CoursePatterns in the Fossil RecordPunctuated Equilibrium: geologic periods of apparent stasis then sudden dramatic changes demonstrated by some speciesother species only show gradual changes coined Gradualism

63. Punctuated Equilibrium

64. Punctuated Equilibrium&Gradualism

65. Speciation Rates

66. Speciation RatesHybrid sunflower that diverged reproductively from parents to form new species over short time periodF1 generation 5% fertilityF5 generation >90% fertile

67. Genetics of Speciationfundamental question for biologists: How many genes must change to form a new species?

68. Single Gene Examplesfound in a few cases:Euhadra snail : single gene resulted in mechanical barrier to reproduction

69. Small # of Genes2 monkey flower species have different pollinators = strong barrier to cross-pollinationMimulus lewisii Mimulus cardinalis

70. Large #s of GenesHybrid of 2 species of fruit fly: Drosophila pseudoobscura results from gene interactions among at least 4 loci

71. Large #s of GenesWestern sunflower: hybrid species thrives in dry sand but 2 parents live in nearby moister environments

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