Natural Selection IIPowerPoint PresentationSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Incipient SpeciationSlide 27Strong CaseNo Choice ExperimentMultiple Choice ExperimentMating Behavior is HeritableSlide 32Reproductive Isolation in Sockeye SalmonSlide 34But they haven’t speciated…RAPID SELECTION(Intense selection, rapid evolution)Natural Selection IINatural Selection•Occurs when individuals differ in their reproductive success•Results in changes in allele frequencies in a population (genetic change over time)Eventually, this leads to morphological changes and, if accompanied by reproductive isolation, speciation.Darwin’s finchesHawian silverswordsArtificial versus rapid natural selectionIs artificial selection analogous to natural selection?YES!*same basic mechanism (differential reproductive success)•NS = fitness related to environment•AS = “fitness” related to human preferenceClassic examples of intense natural selection and subsequent rapid evolution•Antibiotic resistance•Antiviral resistance•Cichlids•Sticklebacks•Pocket mice•Darwin’s finches•Hawian silverswords•Fish in fisheriesSome lesser-known examples:•Snails shell morphology in northern New England•Escape ability in trinidad guppies•Copepods and dinoflagellates (if time)FEATURE EXAMPLES•Oxygen saturation and offspring survival (Becky)•Illustrates mechanisms of evolution•Reproductive isolation in African Drosophila (Raul)•Example of speciationQuestionsHow do these examples provide evidence for evolution?How can we use this information to help non-scientists understand evolution?What are the claims of evolution? What aren’t? What are we still uncertain about?Conditions that favor rapid evolution•Quick generation time•Strong selective pressure•Available ecological niches (as on newly formed islands)long term evolution condensed into a short amount of timeClaims of evolution we’ll address in following examples• Differential survival and reporduction occurs in response to selective pressures•or is change guided by a divine hand?• Change occurs at the population, not individual level •or do individuals pass on acquired characteristics to their offspring?• Natural selection acts only on heritable variation•or do individuals pass on acquired characteristics to their offspring?• Natural selection is adequate to explain speciation and higher taxonomic level differences (common ancestry)•or do species have separate origins?Morphology of Littoria obtusa in 1900•High-spiraled•Thin-walledThe range of Carcinus, an intertidal crab and predator of Littoria obtusa, expanded into northern New England in 1900.The crabs prefer high-spiralled, thin-walled snails to low spiralled, thick walled snails of the same species.EXAMPLE 1Morphology of Littoria obtusa after 1982•Low-spiraled•Thick-walledThe range of Carcinus extended into Nova Scotia by 1986.Laboratory experiments showed that Carcinus prefers high-spiralled, thin-walled snails to low spiralled, thick walled snails.EXAMPLE 1EXAMPLE 1Morphology of snails collected before 1900.Morphology of snails collected after 1982.The predator provided strong selection for low-spiraled, thick-walled snails. Within 82 years, Littoria obtusa underwent dramatic morphological changes.Evidence that populations change in response to selective pressuresEXAMPLE 2Trinidadian guppies and escape abilityEXPERIMENTAL BACKGROUDGuppies were introduced into both high and low predation habitats.Twenty years later, 6 guppies were removed from a low-predation and 6 from a high predation habitat. They were placed in an enclosure with their natural predator, a cihlid. When the cichlid had consumed 1/2 of the guppies, the remaining guppies were removed and scored as to whether they came from high or low predation habitats.FINDINGSGuppies from high-predation populations had a much higher survival rate. Thus, they had improved escape ability.EXAMPLE 2Trinidadian guppies and escape abilityBUT…Is escape ability a heritable trait?F2 generation were tested from low and high predation habitats (bred and raised in predator-free enclosures).FOUND F2s of guppies from high predation populations had significantly greater escape abilityEXAMPLE 2Trinidadian guppies and escape abilityConclusionsEscape ability is acquired rapidly under the strong selection pressure of predation.Escape ability is a heritable trait.Evidence that natural selection acts on heritable variationOffspring survival is greater among women with higher oxygen saturation levels at high elevationsBackgroundPopulations at high altitudes are exposed to hypoxia (Hypoxia stresses the oxygen delivery system)Individuals differ in percent oxygen saturation of hemoglobin despite a uniform environmentOxygen saturation levels are determined by a single locus following Mendelian patterns of inheritance and dominance (locus is inferred only, not yet cloned)Could hypoxia be a selective pressure for higher oxygen saturation levels?THE STUDY•Collected geneaological, oxygen saturation genotype, and female fertility data from 3812 people in 14 villages between 3800 and 4200 m in the Tibet Autonomous Region of China from November 1997 to August 2000•Analyzed data on fertility events and oxygen saturation genotype from a subgroup of 20 - 59 year old married womenFOCUS OF TODAY’S DISCUSSIONGenotype AB and BB oxygen saturation level of hemoglobin 10% higher than AAHigh saturation genotypes were significantly correlated with: SUMMARY OF RESULTS(1) lower infant mortality (2) higher number of surviving offspringFour main claims of evolution indroduced at the beginning • Differential survival and reproduction occurs in response to selective pressures•or is change guided by a dinivne hand?• Change occurs at the population, not individual level •or do individuals pass on acquired characteristics to their offspring?• Natural selection acts only on heritable variation•or do individuals pass on acquired characteristics to their offspring?• Natural selection is adequate to explain speciation and higher taxonomic level differences (common ancestry)•or do species have separate origins?For which claims of evolution does this example provide evidence?How is this an example of evolution?Number of individuals with the BB and AB genotypes increase dramatically
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