Natural Selection II RAPID SELECTION Intense selection rapid evolution Natural 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 Hawian silverswords Darwin s finches Artificial versus rapid natural selection Is artificial selection analogous to natural selection YES same basic mechanism differential reproductive success NS fitness related to environment AS fitness related to human preference Classic examples of intense natural selection and subsequent rapid evolution Antibiotic resistance Antiviral resistance Cichlids Sticklebacks Pocket mice Darwin s finches Hawian silverswords Fish in fisheries Some 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 speciation Questions How 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 time Claims 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 EXAMPLE 1 Morphology of Littoria obtusa in 1900 High spiraled Thin walled The range of Carcinus an intertidal crab and predator of Littoria obtusa expanded into northern New England in 1900 The crabs prefer high spiralled thinwalled snails to low spiralled thick walled snails of the same species EXAMPLE 1 The range of Carcinus extended into Nova Scotia by 1986 Laboratory experiments showed that Carcinus prefers high spiralled thinwalled snails to low spiralled thick walled snails Morphology of Littoria obtusa after 1982 Low spiraled Thick walled Morphology of snails collected before 1900 EXAMPLE 1 The predator provided strong selection for lowspiraled thick walled snails Within 82 years Littoria obtusa underwent dramatic morphological changes Evidence that populations change in response to selective pressures Morphology of snails collected after 1982 Trinidadian guppies and escape ability EXAMPLE 2 EXPERIMENTAL BACKGROUD Guppies 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 FINDINGS Guppies from high predation populations had a much higher survival rate Thus they had improved escape ability Trinidadian guppies and escape ability EXAMPLE 2 BUT 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 ability Trinidadian guppies and escape ability EXAMPLE 2 Conclusions Escape ability is acquired rapidly under the strong selection pressure of predation Escape ability is a heritable trait Evidence that natural selection acts on heritable variation Offspring survival is greater among women with higher oxygen saturation levels at high elevations Background Populations at high altitudes are exposed to hypoxia Hypoxia stresses the oxygen delivery system Individuals differ in percent oxygen saturation of hemoglobin despite a uniform environment Oxygen 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 FOCUS OF TODAY S DISCUSSION Analyzed data on fertility events and oxygen saturation genotype from a subgroup of 20 59 year old married women Genotype AB and BB oxygen saturation level of hemoglobin 10 higher than AA SUMMARY OF RESULTS High saturation genotypes were significantly correlated with 1 lower infant mortality 2 higher number of surviving offspring For which claims of evolution does this example provide evidence Four 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 How is this an example of evolution Natural selection acts only on heritable variation Number of individuals with the BB and AB genotypes increase dramatically with each generation Change occurs at the population not individual level Frequency of B alleles increase in the populations Differential survival and reproduction occurs in response to selective pressures The change in allele frequency in the populations is NATURAL SELECTION due to the intense selective pressure of hypoxia We don t know whether increased survivorship is due to having healthier mothers each individual having higher oxygen saturation level or a combination of the two AA Starting population AB AA BB and
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