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Speciation
How do new species form on the Earth? This question was first asked by Lamarck and Darwin in the 1800's. Today you will complete a simulation and discover one of the mechanisms that contributes to speciation, and as a result, to the diversity of life on Earth. In this simulation, we will travel to the fictitious island of Darwinia to study how geographic and reproductive isolation contribute to the speciation of the insect, Lamarckia chocolata. Materials: small bag of regular M & M's pen/paper or calculator plastic bag Directions: Empty your bag of M & M's onto a table and sort them by color. 1. Count the total number of Lamarckia chocolata (M & M's) in your bag. ____________ 2. Count the number of each color of Larmarckia chocolata in your bag and record these numbers in the data table below. 3. Determine the % or frequency of each color of Lamarckia chocolata by dividing the number of a specific color of M & M by the total number of M & M's. Record this information in the table below in column 2. 4. You are a newly introduced predator to the island of Darwinia. In a search for food, you find a small insect, Lamarckia chocolata, in a variety of forms. However, the DARK BROWN ones are the easiest to capture. As a result, you eat all of the DARK BROWN ones except for ONE. (remove all but one DARK BROWN M & M's from the population.) 5. What effect does this have on the gene pool of this population? 6. What is the future of the DARK BROWN gene in this population? 7. Taking into account the physical or anatomical features of insects, make a list of characteristics that might make the dark brown insects more vulnerable to predation. 8. Put the M & M's into the plastic bag and shake them up. Then pour them out onto a piece of paper. 9. Now assume a GEOGRAPHIC CHANGE has occurred in the area and the population is separated into two groups. (Separate the M & M's into two groups to simulate this.) The size of the two populations does not need to be equal. 10. What is the total number of Lamarckia chocolata in population one (group one)? 11. Fill in the data table above to represent the starting data for trial two and complete the next two trials in the same manner as in step 4 above. 12. Calculate the gene frequencies for population 2 (group two). QUESTIONS 1. What does each M & M represent? 2. What does each color of M & M represent? 3. Using the data in the Data Table, how do the frequencies in the original population compare to the gene frequencies in population 1 and 2? 4. Compare the gene frequencies in the geographically isolated populations 1 and 2. 5. According to your text, what is a species? 6. Explain how geographic isolation changes the gene pool and how it may lead to speciation. 7. Is the speciation observed in this activity a result of allopatric speciation or sympatric speciation? Why? Student Key 1. Each M & M represents an individual insect, Lamarckia chocolatia. 2. Each color represents a different phenotype of the insect. 3. The population of Lamarckia chocolata is higher in the initial population than at the end of the first trial (population 1) due to predation. 4. Answers will vary. 5. Found in your textbook, the primary definition of species used most frequently in this textbook was proposed in 1942 by biologist Ernst Mayr. This defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are unable to produce viable, fertile offspring with members of other populations. 6. As the allele frequencies in the two separate populations change due to sexual reproduction and possibly mutation, they can become more distinct. Eventually, given enough time and as pressure further increases their genetic diversity, the two populations may no longer be able to successfully mate and produce fertile offspring. In this case, the biological species concept would apply and speciation would have taken place. 7. The activity represents an example of allopatric speciation because the speciation is a result of a geographical barrier when the "new island" is formed and the two groups are divided.