BIOB51 lec 1 & 2 readings .docx

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University of Toronto Scarborough
Maydianne Andrade

Tuesday September 11 – lecture one & Thursday September 13 – lecture two Chapter 3 (pg. 73-96 and 97-105) Chapter three – Darwinian Natural Selection 3.1 Artificial Selection: Domestic Animals and Plants Mechanisms of evolution under domestication helped Darwin understand mechanism of evolution in nature Darwin studied the mechanisms that plant and animal breeders used to select for favourable traits Darwin himself was a pigeon breeder Domestic tomato: Solanum lycopersicum Can be found around the world (cultivation & weedy escapee) Domesticated tomatoes can still interbreed with some species of wild tomatoes It was first cultivated by Native Americans and the early explores introduced the tomatoes to Europe (where it began to spread globally) The wild tomato is small (less than a cm in length & weighs only a few grams) The domesticated tomato can now grow large (15cm in length and 1 kg in weight) Molecular Explanation: on chromosome 2 tomatoes carry a gene known as fw2.2, which encodes for a protein, which represses cell division. The size of the fruit depends on the amount of proteins being made. Increased number in protein causes smaller size. Cultivated fruits have fewer proteins, which results in a larger size. Anne Frary & Steven Tanksley demonstrated this phenomenon through experimentation (30% more growth) By selecting for only the large plants (cultivate) they were eliminating the small- fruited alleles Other examples of domesticated plants include: broccoli, Brussels sprouts, cauliflower, kale, & kohlrabi they were derived from Brassica oleracea 3.2 Evolution by Natural Selection Similar processes to artificial selection occurs within nature Darwin wrote his book – On the Origin of Species by Means of Natural Selection Theory of Evolution by natural selection holds that descent with modification is the logical outcome of four postulates 1. Individuals within populations are variable 2. The variations among individuals are, at least in part, passed from parents to offspring (heritable) 3. In every generation, some individuals are more successful at surviving and reproducing than others 4. The survival and reproduction of individuals are not random; instead they are tied to the variation among individuals. The individuals with the most favourable variations, those who are better at surviving and reproducing, are naturally selected 1 Darwinian Evolution: Gradual change in populations over time If there are differences among the individuals in a population that can be passed on to offspring, and if there is differential success among those individuals in surviving and reproducing, then some traits will be passed on more frequently than others. This results in the characteristics of the population to change with each succeeding generation. Darwinian fitness – the ability of an individual to survive and reproduce in its environment Fitness refers to how well an individual survives and how many offspring it produces compared to other individuals of its species. Adaptation – refers to a trait or characteristic of an organism, like a modified form of reverse transcriptase, that increases its fitness relative to individuals Both Darwin and Alfred Wallace discovered the mechanism for evolution independently around the same time. Darwin is given more credit because he thought of it first and had massive documentation in his book. Darwin and Wallace’s four postulates are testable! 3.3 The evolution of Flower Color in an Experimental Snapdragon Population Experimenters: Kristina Niovi Jones & Jennifer Reithel Question: whether natural selection by bumblebees could influence the evolution of a floral trait controlled by alleles of a single gene Experiment: population of 48 snapdragons (postulates one and two were true) then they watched to see if postulates three and four would come true. Postulate one: there is variation among individuals ¾ - pure white with 2 spots of yellow on the lower lip ¼ - yellow all over Varied in colour Postulate two: some of the variation is heritable The gene has 2 alleles (S and s). Genotype SS or Ss will have white flowers while ss will have yellow flowers. Out of the 48 snapdragons 12 were SS, 24 were Ss, and 12 were ss. The colour traits are heritable. Testing Postulate 3: Do individuals Vary in their Success at Surviving or Reproducing? Experiment occurred in a meadow in Colorado, Snapdragons were kept in pots to prevent dying. The experimenters did not intervene for the reproductive aspects. The free-living bees pollinated the plants. The experimenters tracked the number of times the bees visited the plants. To measure the plants’ success at reproducing they counted the number of seeds. Plants showed variation in reproductive success, both as pollen donors and seed mothers. 2 Testing Postulate 4: is reproduction nonrandom? White flowers attracted twice as many bees The white plants produced slightly more seeds per fruit Therefore reproductive success was not random. White plants had a higher reproductive success than yellow plants. Testing Darwin’s Prediction: did the population Evolve? The bees selected particular individuals and granted them high reproductive success. Since the white flowers were favoured, the next generation of snapdragon plants is more likely to be white. And they were more likely by 2% for each generation. 3.4 The Evolution of Beak Shape in Galapagos Finches Observers: Peter Grant & Rosemary Grant What: studies finches in the Galapagos Archipelago Darwin’s finches derived from a small flock of grassquits from Central and South America (2.3 million years ago) Fourteen different species All of them are closely related to one another All of the finches range from about 4 – 6 inches. They are either black or brown The variation exists in beak size and shape The beaks are important for feeding The different beak sizes and shapes allows them to eat different foods Warbler – insects, spiders, and nectar Woodpecker & mangrove – twigs or cactus spine are used to pry insect larvae or termites from dead wood Ground finches – ticks, iguanas, & tortoises Vegetarian finches – leaves & fruits The data was gathered on medium ground finch on Isla Daphne Major The climate is seasonal Vegetation consists of dry forest and scrubs as well as cactus The ground finch is ideal to study because their population is small and lived up to about sixteen years. The generation time is 4.5 years They are seed eating birds Testing Postulate 1: Is the Finch Population Variable? Researchers captured and marked the finches (allowed identification) The scientists weighed, and measured the tail length, beak width, beak depth, and beak length for the captured birds. The variables varied. 3 Testing Postulate 2: Is some of the Variation among individuals Heritable? Beak depth varied due to the difference in environments they experienced or if their genotype differed. Variations in food fed to the birds at infancy can alter or effect beak depth (environmental). Injuries can also affect beak depth (environmental) Peter Boag estimated the heritability of beak depth – strong correspondence Large proportion of the observed variation in beak depth is genetically based and can be passed on to offspring. Other factors such as maternal effects, environment, conspecific nest parasitism, and misidentified paternity can underplay the
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