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Unit 6 natural selection Why do organisms ‘match’ their environment? • the ‘match’ is genetic fitness Natural selection: differential survival and reproduction of individuals based on genetic differences in some trait(s) adaptation • the ‘match’ is induced by environment www.unc.edu/~welcha/.../lecture%203%20natural%20selection.ppt Charles Darwin figured out how natural selection could lead to adaptive evolution. • offspring resemble parents • variation in traits can be inherited • life is full of challenges! • variation in traits variation in fitness Fitness: - ability to survive and reproduce - depends on the environment How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant mutation! How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant Generation 3: 0.76 not resistant 0.24 resistant How natural selection works Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant Generation 3: 0.76 not resistant 0.24 resistant Generation 4: 0.12 not resistant 0.88 resistant Natural selection – key points differential survival and reproduction of individuals based on genetic differences in some trait(s) For adaptations to evolve: - differences in the trait must cause differences in fitness - differences in the trait must be heritable Fitness depends on the environment. local adaptation Testing for local adaptation color polymorphism among male guppies streams with effective predators streams with ineffective predators streams with no predators How can we test whether the difference in coloration is an adaptation? What other explanations are possible? Testing for adaptation: reciprocal transplant experiment guppies from no predator stream moved to stream with effective predators control control effective predators no predators guppies from stream with effective predators moved to no predator stream (Endler, 1980) Testing for adaptation: reciprocal transplant experiment guppies from no predator stream moved to stream with effective predators control control effective predators no predators guppies from stream with effective predators moved to no predator stream Who do we move? Why the controls? What happens?? Testing for adaptation: reciprocal transplant experiment after one generation effective predators no predators Testing for adaptation: reciprocal transplant experiment Is difference between environments genetic or induced by the environment? Does the population adapt? common garden experiment Is difference between environments genetic or induced by the environment? Testing for adaptation: reciprocal transplant experiment after one generation effective predators no predators Testing for adaptation: reciprocal transplant experiment after one generation effective predators no predators Testing for adaptation: reciprocal transplant experiment after one generation effective predators no predators after 15 generations effective predators no predators Testing for adaptation: reciprocal transplant experiment Is difference between environments genetic or induced by the environment? Does the population adapt? common garden experiment Is difference between environments genetic or induced by the environment? Natural selection – key points For adaptations to evolve: - differences in the trait must be heritable - differences in the trait must cause differences in fitness Fitness depends on the environment. local adaptation Natural selection can cause populations to diverge. Natural selection can cause populations to diverge. divergence Divergence can lead to new species. More evidence for adaptations wings of birds wings of damselflies what about wings of butterflies? wings = adaptations for flight (similar by function not descent) unrelated organisms adapt independently to a common environment. Convergent evolution – natural selection has matched unrelated species to a common environmental challenge.