BIOB 272 1st Edition Lecture 24Outline of Last Lecture Coalescence and GenealogiesI. Coalescence and Gene TreeII. Mitochondrial DNAIII. Effects Differing Coalescence Time For Different Genesa. On Selectioni. Directional Selectionii. Balancing Selectionb. Gene Trees don’t Always match Species TreesOutline of Current Lecture Natural Selection in the WildI. Modes of Selectiona. Directionalb. Stabilizingc. DisruptiveII. Case Study 1: Diversity in Darwin’s FinchesIII. Case Study 2: Coat Color in the Old Field Mouse: PeromyscusPolionotusIV. Case Study 3: Color Variation in KingsnakesV. Case Study 4: Gall Flies and GallsCurrent LectureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Natural Selection in the WildI. Modes of Selectiona. Directionalb. Stabilizingc. DisruptiveII. Case Study 1: Diversity in Darwin’s Finches- Molecular phylogenies reveal a single commonorigin for Darwin’s finches- Variation in beak size influences efficiencyat eating different types of seeds- Beak width is heritable- Trait variationinfluences fitnessvariationo Drought: changed mean beak size- bigger beaks= greater chance of survival because could eat the seeds better= they had babies who had similar beakso Heavy rains= better chance of survival with smaller beaks= they had babieso Selections varied three times, so average beak size changed 3 times- Directional Selection can vary over time- Directional selection favors increases ordecreases in the mean of a trait- Stabilizing selection favors average valuesof a trait- Long-term studies reveal fluctuation in thedirection and strength of natural selectionIII. Case Study 2: Coat Color in the Old Field Mouse: PeromyscusPolionotus- Coat color variation affects fitness because of directional selection- White coat color along white beaches, dark coat color inland - Trait influenced by multiple genes- Agouti and Mclr- Same genetic variations at both places the light colored mice evolved in Florida?o Independent evolution of “light” phenotypeo Mclr light allele only associated with light color in Gulf populationo Independent and convergent evolution- Evolution in response to natural selectionis inevitable if:– There is variation in a trait– Variation is heritable– Some variants reproduce more than others- Specific features of the environment cangenerate natural selection on a trait- Common selective pressures can result inconvergent evolution, often throughdistinct genetic mechanismsIV. Case Study 3: Color Variation in Kingsnakes- Color difference= genetic difference due to population structure or different structure across the range?- Genetic studies indicate extensive gene flow (migration) across the range of the Scarlet kingsnake – suggesting that differences do not represent genetic isolation between populations.- Aposematism: An antipredator strategy used by potential prey to signal danger or a lack of palatability. Commonly manifest through bright coloration to warning potential predators.- Predators attack less in areas where coral snakes co-occur- Kingsnakes show more striking color contrast (brightness) in areas where coral snakes co-occuro Rules out population structure so it’s an aposematic= bright colorscommon with venomous species to keep away predatorso Areas where venomous and nonvenomous but look venomous (mimics)o Higher correlation of mimics with coral snakes- Natural selection can lead to variation overthe geographic range of a species. That is, an allele may experience no, positive, or negative selection dependingon the environment.V. Case Study 4: Gall Flies and Galls- Gall flies lay eggs in the tips of goldenrod plants. Hatched larva bore into plant tissue to feed. They secret fluids that induce the plant to growtumor like galls which nourish & protect the larvae - Extended phenotype: Structures constructed by organisms that can influence their fitness. Though they are not a part of the organism they reflect the organisms genotype- Gall diameter is variable and heritable- Large galls are more often preyed upon by woodpeckers- Smaller galls are more often preyed upon by parasitic wasps= Selection against too large and too small
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