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Evolution: MacroevolutionMicroevolution: changes on the small scaleChanges in gene frequencies in a populationMacroevolution: changes on the large scaleSpecies FormationEarth is home to numerous speciesEstimates range between 10 and 25 million species4 million species is lowest estimatePresent species are survivors or newcomers99% of all species that have ever lived on Earth are now extinctWhat Is a Species?All of the species on Earth share a common ancestor ~3.8 billion years agoInitial type of organisms branched into two types of organismsNew “species”Species FormationProcess continued, producing all of the species that have ever lived on the planetThese species branched furtherNew species are formed after populations of a single species stop interbreedingWhat Is a Species?Biological species conceptSpecies are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groupsWhat Is a Species?Some separate species may be able to interbreed in captivity, but do not do so in naturee.g., Lion ♂ + tiger ♀  ligere.g., Lion ♀ + tiger ♂  tigonSince this interbreeding does not occur in nature, lions and tigers are separate speciesMythical powersWhat Is a Species?The biological species concept is not always sufficient in defining speciesMany bacteria reproduce asexually, not sexuallyThere is sometimes limited very limited gene flow between two speciesHow Do New Species Arise?“Speciation” is the development of new species through evolutionBranches from parent species, while parent species continues to existSpeciation results from the same processes operating in microevolution (changes in allaele frequencies in the population)How Do New Species Arise?Evolution within a population involves a change in the population’s allele frequenciesTwo interbreeding populations will share any changes in allele frequenciesThese populations will evolve together and remain a single speciesHow Do New Species Arise?Two populations that do not interbreed will not share changes in allele frequenciesChanges will add up over timeUltimately, a new species could be formedHow Do New Species Arise?Allopatric speciationGeographic separation can restrict gene flow between populationsGlaciers can move into an areaA river can change coursePonds can dry upPart of a population may migrate into a remote area (e.g., Galápagos Islands, Hawaiian Islands, etc.)How Do New Species Arise?Allopatric speciationRestricted gene flow between two populations can ultimately result in the formation of a new species“Allopatric speciation”How Do New Species Arise?During their geographic separation, allele frequencies of two populations will change differentlyThese populations will evolve differentlyPhysical or behavioral changes may resultHow Do New Species Arise?When two geographically separated populations are reunited, they may or may not be able to interbreedIf not, then speciation has occurredHow Do New Species Arise?Mechanisms preventing interbreeding are central to speciationMountains and rivers are extrinsic isolating mechanismsCharacteristics of the organisms are intrinsic isolating mechanismsHow Do New Species Arise?Intrinsic reproductive isolating mechanismsAny factor that prevents interbreeding of individuals of the same or closely related speciesAllopatric speciation involves extrinsic isolation (geographic separation) followed by the development of intrinsic isolating mechanismsHow Do New Species Arise?Intrinsic reproductive isolating mechanismsEcological isolationTemporal isolationBehavioral isolationMechanical isolationGametic isolationHybrid inviability or infertilityHow Do New Species Arise?Ecological isolationTwo species may feed, mate, and grow in different habitats within a common areae.g., Ranges of lions and tigers overlappedLions preferred the open grasslandsTigers preferred the deep forestsNo interbreeding occurredHow Do New Species Arise?Ecological isolationTwo species may feed, mate, and grow in different habitats within a common areae.g., Ranges of lions and tigers overlappedLions preferred the open grasslandsTigers preferred the deep forestsNo interbreeding occurredHow Do New Species Arise?Behavioral isolationIndividuals choose their mating partnersThis choice is often dependent upon courtship ritualsClosely related species may have incompatible courtship ritualse.g., Songs of birds and crickets, fiddler crab claw waving, etc.How Do New Species Arise?Mechanical isolationReproductive organs of two closely related species may have incompatible sizes or shapese.g., Different butterfly species have genitalia that differ in shapeHow Do New Species Arise?Gametic isolationMating may occur, but the sperm is incompatible with either the egg or the female reproductive systemHow Do New Species Arise?Gametic isolatione.g., Sperm in pollen of one plant species cannot reach egg of related speciese.g., Sperm of one animal species is killed in reproductive system of related speciese.g., Sperm of one species cannot bind to receptors on egg of related speciesHow Do New Species Arise?Hybrid inviability or infertilityOffspring resulting from a mating between closely related species may be unhealthyOffspring resulting from a mating between closely related species may be infertilee.g., Horse + donkey  muleMules are healthy, but infertile hybridsSympatric SpeciationThe fruit fly Rhagoletis pomonella provides one of the best-studied examples of sympatric speciationSympatric SpeciationR. pomonellaOriginally existed solely on hawthorn trees“Haw flies”Some moved to apple trees newly introduced from EuropeFlies colonizing apple trees are becoming a new species“Apple flies”Sympatric SpeciationHaw fly life cycleThese flies winter underground as larvaAdult flies emerge in the summerFlies fly to their host trees, mate, and lay their eggs in the fruitAdult flies live for approximately one monthSympatric SpeciationA mutation or new combination of existing rare alleles arose in the ancestral haw fliesSympatric SpeciationMutant flies emerged earlier in the summerThese flies were attracted to apples as well as hawthornsApples mature slightly earlier than hawthorn fruitThese early emerging flies interbred amongst themselves to a high degreeLimited gene flow between these populationsSympatric SpeciationMating periods of “haw flies” and “apple flies” do not fully overlapTemporal isolationThese two types of flies occupy different habitats in


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LBCC BIO 41 - Macroevolution

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