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- 1. The Origin ofThe Origin of SpeciesSpecies BIOLBIOL 102:102: General Biology IIGeneral Biology II ChapterChapter 2424 RobRob SwatskiSwatski Associate ProfessorAssociate Professor of Biologyof Biology HACCHACC--YorkYork 1
- 2. SpeciationSpeciation Explains how new species originate & how populations evolve Microevolution: adaptations that evolve within a population’s gene pool Macroevolution: evolutionary change above the species level Macroevolution is the cumulative effect of many speciation & extinction events MicroevolutionMicroevolution2
- 4. Macroevolution of TechnologyMacroevolution of Technology 4
- 5. How isHow is PhylogenyPhylogeny Determined?Determined? Morphology Physiology Biochemistry DNA sequences 5
- 6. BiologicalBiological SpeciesSpecies ConceptConcept A group of populations whose members have the potential to interbreed in nature … ... & produce viable, fertile offspring They do not breed successfully with other populations Gene flow between populations holds the phenotype together 6
- 7. Similarity between twoSimilarity between two differentdifferent speciesspecies Eastern meadowlark Western meadowlark 7
- 8. DiversityDiversity withinwithin a speciesa species The biological species conceptThe biological species concept isis notnot based on physical similaritybased on physical similarity8
- 9. ReproductiveReproductive IsolationIsolation Biological factors (barriers) that prevent 2 different species from mating & producing offspring (hybrids) Reproductive isolation is classified by whether factors act before or after fertilization Prezygotic barriers & Postzygotic barriers 9
- 10. Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation Gametic Isolation Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown Individuals of different species MATING ATTEMPT FERTILIZATION VIABLE, FERTILE OFFSPRING (a) (c) (e) (d) (b) (g) (k) (h) (i) (j) (l)(f) PrezygoticPrezygotic BarriersBarriers PostzygoticPostzygotic BarriersBarriers 10
- 11. PrezygoticPrezygotic BarriersBarriers Block fertilization by:Block fertilization by: Impeding different species from attempting to mate Preventing the successful completion of mating Hindering fertilization if mating is successful 11
- 12. Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation Gametic Isolation Individuals of different species MATING ATTEMPT FERTILIZATION (a) (c) (e) (f) (b) (g) (d) PrezygoticPrezygotic BarriersBarriers 12
- 13. HabitatHabitat IsolationIsolation Two species rarely or never encounter each other … … because they occupy different habitats … … but are not isolated by physical barriers Ex: sticklebacks & garter snake species 13
- 14. St. Lawrence SeawaySt. Lawrence Seaway 14
- 15. Water-dwelling garter snake Thamnophis Terrestrial Thamnophis 15
- 16. TemporalTemporal IsolationIsolation Species that breed at different times of the day, … seasons or years … … & cannot mix their gametes Ex: toads & spotted skunks 16
- 18. Eastern spotted skunk (Spilogale putorius) - mates in late winter Western spotted skunk (Spilogale gracilis) - mates in late summer 18
- 19. BehavioralBehavioral IsolationIsolation Behaviors unique to a species are effective barriers Courtship rituals Displays Vocalizations 19
- 20. BlueBlue--Footed BoobyFooted Booby Courtship RitualCourtship Ritual 20
- 21. Bush Cricket MatingBush Cricket Mating DisplayDisplay 21
- 23. MechanicalMechanical IsolationIsolation Morphological differences can prevent successful mating Anatomical structures evolve differently Body plans are misaligned 23
- 24. Genital openings are not in alignment Bradybaena species with shells spiraling in opposite directions 24
- 26. GameticGametic IsolationIsolation Sperm from one species cannot fertilize eggs of another species Proteins on gamete surfaces cannot bind to each other Ex: sea urchins 26
- 27. PostzygoticPostzygotic BarriersBarriers Prevent hybrid zygote from developing into a viable, fertile adult Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown 27
- 28. Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown FERTILIZATION VIABLE, FERTILE OFFSPRING (k) (h) (i) (j) (l) PostzygoticPostzygotic BarriersBarriers 28
- 29. ReducedReduced HybridHybrid ViabilityViability Genes of different parent species may interact & impair hybrid development May lead to incomplete development of young Results in weak, frail, & infertile offspring Ex: salamander (Ensatina) hybrids 29
- 30. ReducedReduced HybridHybrid FertilityFertility Hybrid development may also be impaired in other ways Even if hybrids are vigorous, they may be sterile Meiosis in hybrids does not produce normal gametes Ex: donkeys & horses have different #’s of chromosomes 30
- 31. MuleMule (sterile hybrid)(sterile hybrid) 31
- 32. HybridHybrid BreakdownBreakdown Some 1st generation hybrids can be fertile… … but, when they mate with another species (or with either parent species) … … offspring of the next generation will be feeble or sterile Offspring carry too many recessive alleles 32
- 33. Hybrid Rice CultivarsHybrid Rice Cultivars 33
- 34. Limitations ofLimitations of the Biologicalthe Biological SpeciesSpecies ConceptConcept The biological species concept cannot be applied to: Fossils Asexual organisms Prokaryotes Why Not?Why Not? Why not?Why not?34
- 35. One Species … or Two?One Species … or Two? 35
- 36. Grizzly bear (U. arctos) Polar bear (U. maritimus) Hybrid “grolar bear” 36
- 37. Alternative Definitions ofAlternative Definitions of “Species”“Species” Emphasize the unity within a species, not the separateness between different species Morphological species concept Ecological species concept Phylogenetic species concept 37
- 38. MorphologicalMorphological SpeciesSpecies ConceptConcept Defines a species by it’s anatomical features Applies to both asexual & sexual species … but relies on subjective criteria Which structures distinguish a species? 38
- 39. 39
- 40. EcologicalEcological SpeciesSpecies ConceptConcept Defines a species by its ecological niche Also applies to both asexual & sexual species Emphasizes the role of disruptive selection Ex: barnacle species 40
- 41. 41
- 42. PhylogeneticPhylogenetic SpeciesSpecies ConceptConcept Defines a species as the smallest group of individuals on a phylogenetic tree Also applies to both asexual & sexual species It can be difficult to determine the degree of difference required for separate species Ex: slime molds 42
- 43. 43
- 44. SpeciationSpeciation Allopatric Speciation Speciation with geographic isolation (“other country”) Sympatric speciation Speciation without geographic isolation (“same country”) 44
- 45. Allopatric speciation Sympatric speciation 45
- 46. AllopatricAllopatric SpeciationSpeciation Gene flow is interrupted or reduced … … when a population is divided into geographically isolated subpopulations Ex: habitat fragmentation 46
- 47. Habitat FragmentationHabitat Fragmentation in the Amazon Rainforestin the Amazon Rainforest 47
- 48. 48
- 49. A. harrisi A. leucurus Harris’s antelope squirrel (South rim) White-tailed antelope squirrel (North rim) 49
- 50. Mechanisms ofMechanisms of AllopatricAllopatric SpeciationSpeciation Mutation Natural Selection Genetic Drift 50
- 51. (a) Under high predation (b) Under low predation Reproductive isolation as a by-product of selection: Mosquitofish 51
- 52. Evidence ofEvidence of AllopatricAllopatric SpeciationSpeciation Regions with many geographic barriers … … usually have more species than regions with fewer barriers Ex: tropical rain forest frogs 52
- 53. A. formosus Atlantic Ocean A. nuttingi Isthmus of PanamaIsthmus of Panama Pacific Ocean A. panamensis A. millsae Allopatric speciation in snapping shrimp (Alpheus) – sibling species 53
- 54. Geographic distance (km) Degreeofreproductiveisolation 0 0 50 100 150 250200 300 0.5 1.0 1.5 2.0 Dusky salamandersDusky salamanders Reproductive isolation increases as the distance between populations increases 54
- 55. Sympatric SpeciationSympatric Speciation Occurs in geographically overlapping populations Polyploidy Habitat Differentiation Sexual Selection Hybrid Zones 55
- 56. PolyploidyPolyploidy The presence of extra sets of chromosomes due to accidents of cell division Much more common in plants than in animals (flatworms, leeches, salamanders, tree frogs) Occurs in many important crops: oats, cotton, potatoes, tobacco, & wheat Autopolyploidy & Allopolyploidy 56
- 57. 57
- 58. 2n = 6 4n = 12 Failure of cell division after chromosome duplication gives rise to tetraploid cells 2n Gametes produced are diploid. 4n Offspring with tetraploid karyotypes may be viable & fertile & become new species AutopolyploidyAutopolyploidy A new species with 2 or more chromosome sets, derived from one species 58
- 59. Species A 2n = 6 Normal gamete n = 3 Meiotic error Species B 2n = 4 Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Unreduced gamete with 7 chromosomes Normal gamete n = 3 New viable fertile hybrid species* (allopolyploid) 2n = 10 *The 2n chromosome # of the new species = the sum of the 2n chromosome #’s of the parent species AllopolyploidyAllopolyploidy A new species with multiple sets of chromosomes, derived from 2 different species 59
- 60. HabitatHabitat DifferentiationDifferentiation Sympatric speciation can also result from the appearance of new ecological niches Ex: North American maggot fly Lives on native hawthorn trees & more recently introduced apple trees 60
- 61. Apples (new habitat) Hawthorns (original habitat) 61
- 62. SexualSexual SelectionSelection Can also drive sympatric speciation Selection for mates of different colors led to speciation Ex: cichlids in Lake Victoria 62
- 63. 63
- 64. EXPERIMENTEXPERIMENT Normal light Monochromatic orange light Pundamilia pundamilia P. nyererei Females mated with males of both species Females only mated with males of their own species 64
- 65. HybridHybrid ZonesZones Regions where members of different species mate & produce hybrids Provide opportunities to study factors that cause reproductive isolation Ex: swordtails (Xiphophorus) 65
- 66. 66
- 67. PatternsPatterns Within HybridWithin Hybrid ZonesZones Hybrids can occur in a single band where adjacent species meet Hybrids often have reduced fitness compared with parent species Hybrid zone distribution can be more complex if parent species are found in multiple habitats within the same region 67
- 69. Frequencyof B.variegata-specificallele Yellow-bellied toad range Hybrid zone Fire-bellied toad range Distance from hybrid zone center (km) 40 0.99 0.9 0.5 0.1 0.01 30 20 10 0 10 20 69
- 70. Possible Outcomes ofPossible Outcomes of Hybrids Over TimeHybrids Over Time Reproductive barriers become stronger Reproductive barriers become weaker Hybrid individuals continue to form 70
- 71. Gene flow Population (5 individuals are shown) Barrier to gene flow Isolated population diverges Hybrid zone PossiblePossible outcomes:outcomes: Reinforcement OR OR Fusion Stability Hybrid 71
- 72. ReinforcementReinforcement Occurs when hybrids are less fit than their parent species Over time, hybrids gradually stop forming Reproductive barriers become stronger 72
- 73. Sympatric male pied flycatcher Allopatric male pied flycatcher 73
- 74. Pied flycatchers Collared flycatchers 28 24 20 16 12 8 4 0 (none) NumberoffemalesNumberoffemales Females matingFemales mating with males from:with males from: Own species Other species Sympatric malesSympatric males Own species Other species AllopatricAllopatric malesmales 74
- 75. Pundamilia nyererei Pundamilia pundamilia Pundamilia “turbid water,” hybrid offspring from a location with turbid water FusionFusion Occurs when hybrids have the same fitness as both parent species There can be significant gene flow between species Reproductive barriers weaken If gene flow is high enough, parent species can fuse into a single species 75
- 76. StabilityStability Continued production of hybrid individuals Extensive gene flow from outside the hybrid zone can overwhelm selection for increased repro isolation inside the hybrid zone The resulting 1st or 2nd generation hybrid offspring are less fit than either parent species 76
- 77. SpeciationSpeciation Can occur slowly or rapidly Can result from changes in few or many genes How long does it take for new species to form? How many genes need to differ between species? 77
- 78. Speciation Patterns CanSpeciation Patterns Can Be Studied Using:Be Studied Using: The Fossil Record Morphological Data Molecular Data 78
- 79. Patterns inPatterns in the Fossilthe Fossil RecordRecord Species may appear suddenly, persist essentially unchanged for some time, & then apparently disappear Niles Eldredge & Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change This contrasts with the gradual change model 79
- 81. SpeciationSpeciation RatesRates The punctuated pattern in the fossil record & lab studies suggests that speciation can be rapid The interval between speciation events can range from: 4000 years (cichlids) to… 40 million years (some beetles) 81
- 82. Rapid Speciation ofRapid Speciation of HelianthusHelianthus anomalusanomalus 82
- 83. H. annuus gamete H. petiolarus gamete F1 experimental hybrid (4 of the 2n = 34 chromosomes are shown) EXPERIMENT RESULTS Chromosome 1 H. anomalus Chromosome 2 H. anomalus Experimental hybrid Experimental hybrid 83
- 84. Studying theStudying the Genetics ofGenetics of SpeciationSpeciation Genomics enables researchers to identify specific genes involved in some cases of speciation Speciation might require the change of only one allele … … or many alleles 84
- 86. (a) Typical Mimulus lewisii (b) M. lewisii with an M. cardinalis flower-color allele A Locus That Influences Pollinator Choice:A Locus That Influences Pollinator Choice: Monkey flowersMonkey flowers 86
- 87. (c) Typical Mimulus cardinalis (d) M. cardinalis with an M. lewisii flower-color allele 87
- 88. 88 CreditsCredits by Rob Swatski, 2013 http://robswatskibiology.wetpaint.com Visit my website for moreVisit my website for more Biology studyBiology study resources!resources! http://www.flickr.com/photos/rswatski Please send your comments and feedback to: rjswatsk@hacc.edu This work bears an Attribution-Noncommercial Share Alike Creative Commons license. Images used in this work bear a Creative Commons license and are attributed to their original authors.