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Lecture 3

by: Sierra

Lecture 3 Biol 28600


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Notes from Lecture 3
Introduction to Ecology and Evolution
Joshua Springer
Class Notes
Ecology, evolution, Biology
25 ?




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This 27 page Class Notes was uploaded by Sierra on Thursday February 11, 2016. The Class Notes belongs to Biol 28600 at Purdue University taught by Joshua Springer in Spring 2016. Since its upload, it has received 18 views. For similar materials see Introduction to Ecology and Evolution in Biology at Purdue University.


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Date Created: 02/11/16
Sometimes, evolution sucks! Housekeeping • You should be able to see what you got incorrect on Quiz 1 now – Look over your answers – Look at questions you were not assigned from the total pool of 17 • Quiz 2 will be posted Thursday after class • Grades from Mastering are not immediately available on Blackboard; be patient Housekeeping • Office Hours for the TAs start this week! – If you have any questions they can help • Start recording iClicker points today! – Bring iClicker to every lecture from today onward Natural Selection ‘chooses’ the best adapted • For the current generation ONLY • Not necessarily the best adapted for the next or subsequent generations – lookingon by natural selection is NOT forward- – It is not a ‘thinking process’ • Sorts through allelic combinations that ‘work’ or don’t work for the present – (alleles= versions of a gene) Size Matters Male mosquitofish (Gambusia affinis) Gonadopodium Evolution by Natural Selection DOES NOT lead to perfection! See page 780 of your text iClicker (set to AA) • What is one main reason why an HIV infection can change in a person over time? – A) Errors in transcription accumulate – B) more than one virus actually gets transferred from person to person – C) body heat leads to virus changes – D) nature just wants it to be that way iClicker (set to AA) • What is the hypothesis that was proposed to explain the spillover event of HIV to humans? – A) Bantu hypothesis – B) Cut-hunter hypothesis – C) The traveler hypothesis – D) Hybrid virus hypothesis – E) I don’t know How Does Evolution by Natural Selection Work? Darwin’s Four Postulates: 1.Individuals within populations are variable 2.This variation is at least partly heritable (passed from parent to offspring) 3.In every generation, some individuals survive and reproduce better than others 4.Differential reproductive success is tied to the variation among individuals (not random) The trait composition of the population then changes TESTABLE ideas (not just storytelling) “Darwinian fitness”: the ability of an individual to survive and reproduce in its environment NEVER say a ‘Final Population! iClicker (set to AA) • What is a drug holiday? – A) Take extra drugs to knock HIV levels down – B) A short break from HIV drugs – C) A national holiday – D) HIV specific drugs are free to patients – E) What happens when you go to Colorado The Galapagos Finches, a very brief history 1973 Peter and Rosemary Grant (British Evolutionary Biologists) begin studying finch characteristics and environmental conditions on Galapagos Islands Saw evidence for evolution (change in beak characteristics) in just a few years severe droughts led to changes in population structure! SO, think in the long-term: how can a population change dramatically All species on Earth are subject to evolution—none are exempt or special Why have some species not changed in millenia? Medium ground finches in the Galápagos are variable for beak depth That variation is heritable (offspring get characteristics from their parents) Some survive better than others and that’s tied to traits Always pay attention to axes on graphs! And the population evolves Beak size in Darwin’s finches: Wet years: small-beak birds do better Dry years: big-beak birds do better cryptic peppered moths (Kettlewell): industrial soot favored melanistic form, cleaner air favored return to light form. Adaptation with survival advantage when avian predators (as shown by field experiments) “Adaptation”: heritable trait that confers a fitness advantage to its carrier (by improving the reproductive success of the carrier, and thereby the transmission of that trait) Can be sharper teeth, stronger wings, winning smile … We also speak of individuals “adapting” to changes, but this is “acclimatization” (winter fur) or “phenotypic variation” (faster growth in south) Transplant experiments can separate genetically encoded adaptation from environmentally induced phenotypic variation. Fitness • Proximate: ability of an organism to survive and reproduce • Ultimate: relative representation of alleles in subsequent generations • Measures of fitness – Absolute fitness: survival and reproduction of each genotype – Relative fitness: ability of one genotype to survive and reproduce relative to another 3 ways selection acts on a trait: (moths, finches) Genetic Variance • Stabilizing selection on quantitative traits reduces genetic variance – extreme individuals are selected out of the population • Balancing selection in Mendelian traits maintains genetic variation – Both alleles are maintained with heterozygote advantage Frequency Dependent Selection • Fitness of a phenotype affected by commonness of phenotypes • Disruptive selection results when rare phenotypes have higher reproductive success than common phenotypes Phenotype vs. Genotype? • Phenotype is the result of the genotype (in part)—the outward appearance or characteristic • Genotype is the specific allele or alleles that code for a physical characteristic or trait (or physiological functioning) What Evolution is not… • Perfect (we, as humans sometimes think things are perfect) • A cause to ‘believe in’ irreducible complexity (the idea that something is so complex it couldn’t have evolved) – Vertebrate eye – Flagella or cilia ‘motors’ • Untestable – We test it all the time – It took 70 years to become an accepted theory! Next time: • The Five Evolutionary Forces – Reading and videos on Blackboard – More iClicker questions


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