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Chapter 24. The Origin of Species. “Both in space and time, we seem to be brought somewhat near to that great fact—that mystery of mysteries—the first appearance of new beings on this Earth.” — Darwin. What is a species?. Biological species concept defined by Ernst Mayr - PowerPoint PPT Presentation


Chapter 24.

Chapter 24.The Origin of SpeciesBoth in space and time, we seem to be brought somewhat near to that great factthat mystery of mysteriesthe first appearance of new beings on this Earth. Darwin

AP BiologyAP Biology1

What is a species?Biological species conceptdefined by Ernst Mayrpopulation whose members can interbreed & produce viable, fertile offspringreproductively compatible

AP Biology2Biological species conceptEastern Meadowlark

Western MeadowlarkSimilar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreedingAP Biology3

Diversity & TaxonomyThe Tree of Lifespecies are the smallest unit at the ends of branchesbasic unit for organizing & categorizing living things smallest unit by which we measure diversityAP Biology4

How and why do new species originate?Reproductive isolation biological barriers that impede members from producing viable offspringbefore vs. after fertilizationpre-zygotic barriers before the zygotepost-zygotic barriersafter the zygote

AP Biology5Pre-zygotic barriersImpede mating or hinder fertilization if mating occurshabitat isolationtemporal isolationbehavioral isolationmechanical isolationgametic isolation

male Frigate bird displaying to attract femalesAP Biology6Ecological isolationTwo species may occupy different habitats within same area so may encounter each other rarely

2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

lions & tigers could hybridize, but they live in different habitats: lions in grasslands tigers in forestAP Biology7

Temporal isolationSpecies that breed during different times of day, different seasons, or different years cannot mix gametesEastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

AP Biology8Behavioral isolationCourtship rituals that attract mates & other unique behaviors to a species are effective reproductive barriersBlue footed boobies mate only after a courtship display unique to their species

AP Biology9The most comedic species of the Galapagos Islands is the Blue Footed Booby, what a ridiculous outfit and expression! Their name is in fact taken from the Spanish 'bobo' which means clown.The Blue Footed Boobies above display part of their humorous courtship ritual whereby they raise their feet one at a time and then swivel their heads away from the prospective mate looking to the sky.Other interesting Booby features are the highly evolved airbag systems in their skulls which allow them to dive bomb into the sea for fish from great height, and the egg and hatchling nesting boundaries they make which are rings of Boobie poop. They aren't the only Booby on the island there are also Masked and Red Footed Boobies about.

Mechanical isolationMorphological differences can prevent successful matingFor many insects, male & female sex organs of closely related species do not fit together, preventing sperm transferlack of fit between sexual organs: hard to imagine for us, but a big issue for insects with different shaped genitals!

Damsel fly penisesAP Biology10The selection is intense because it directly affects offspring production -- it is affecting sex itselfGametic isolationSperm of 1 species may not be able to fertilize eggs of another speciesvariety of mechanismschemical incompatibility sperm cannot survive in female reproductive tractbiochemical barrier so sperm cannot penetrate eggreceptor recognition: lock & key between egg & spermSea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different speciesred & purple are unable to fuse.AP Biology11Postzygotic barriersprevent hybrid zygote from developing into a viable, fertile adultreduced hybrid viabilityreduced hybrid fertilityhybrid breakdown


AP Biology12Reduced hybrid viabilityGenes of different parent species may interact & impair the hybrids developmentSpecies of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

AP Biology13Horses have 64 chromosomes(32 pairs)Mules have 63 chromosomes!Mule are vigorous, but sterileReduced hybrid fertilityEven if hybrids are vigorous they may be sterilechromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes

Donkeys have 62 chromosomes(31 pairs)

AP Biology14Whats wrong with having 63 chromosomes?Odd number! Cannot pair up in meiosis.Hybrid breakdownHybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterileIn strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.On path to separate species.

AP Biology15

SpeciationSpecies are created by a series of evolutionary processespopulations become isolatedreproductively isolatedgeographically isolatedisolated populations evolve independentlyIsolationallopatricphysical separationsympatricstill live in same areaAP Biology16Allopatric speciation Allopatric = other country geographic separation migration physical barrier

Harriss antelope squirrel inhabits the canyons south rim (L). Just a few miles away on the north rim (R) lives the closely related whitetailed antelope squirrel AP Biology17

Sympatric speciationSympatric = same country some type of isolation even though populations live in same areawhat causes this isolation? behavioral differencesnon-random mating physiological differenceschromosomal changes polyploidymostly in plants: oats, cotton, potatoes, tobacco, wheat

AP Biology18

Adaptive radiationEvolution of many diversely adapted species when introduced to various new environmental challenges & opportunities

DrosophilaGeospizaAP Biology19Adaptive radiationMany ecological niches openEvolution of many diversely-adapted species from a common ancestor to fill nichesDarwins finchesmammals

AP Biology20

ReviewSpeciation is a processpopulations become isolatedgeographic isolationdifferent environmental conditionsfood, predators, disease, habitat different selection pressuresgenetic driftreproductive isolationdifferent selection pressuressexual selectionisolated populations evolve independentlyAP Biology21Niles EldredgeCuratorAmerican Museum of Natural HistoryCurrent debateDoes speciation happen gradually or rapidly perhaps in response to environmental changeGradualismCharles DarwinCharles LyellPunctuated equilibriumStephen Jay GouldNiles Eldredge

AP Biology22Gradualism Gradual divergence over long spans of timeassume that big changes occur as the accumulation of many small ones

AP Biology23Punctuated Equilibrium

Rate of speciation is not constantspecies undergo most change when they 1st bud from parent populationas separate species, remain static for long periods of timeTimeAP Biology24Evolution is not goal-oriented

An evolutionary trend does not mean that evolution is goal oriented. The modern horse is the only surviving twig of an evolutionary tree with many divergent trends.

It does not represent the peak of perfection. There is compromise & random chance involved as well

Remember that for humans as well!AP Biology25Some interesting evolutionary trends.

AP BiologyAP Biology26

Convergent evolutionFlight evolved 3 separate timesevolving similar solutions to similar problems

AP Biology27

Parallel EvolutionFill similar niches; have similar adaptations, but are not closely relatedNichePlacental MammalsAustralian MarsupialsBurrowerMoleAnteaterMouseLemurFlyingsquirrelOcelotWolfTasmanian wolfTasmanian catSugar gliderSpotted cuscusNumbatMarsupial moleMarsupial mouseAnteaterNocturnalinsectivoreClimberGliderStalkingpredatorChasingpredator

AP Biology28

Mimicryconvergent evolution based on similar (protective) appearance

Monarch malepoisonousViceroy maleedible

AP Biology29CoevolutionPredator-prey relationshipsParasite-host relationshipsFlowers & pollinators

AP Biology30Darwin AwardsNamed in honor of Charles Darwin, the father of evolution, the Darwin Awards commemorate those who improve our gene pool by removing themselves from it. The Darwin Awards salute the improvement of the human genome by honoring those who accidentally kill themselves in really stupid ways. Of necessity, this honor is bestowed posthumously.

AP Biology31It's pretty much my favorite animal. It's like a lion and a tiger mixed... bred for its skills in magic.

Any Questions?AP BiologyAP Biology32