Reference no: EM133555569

Biology: evolution and ecology (breeders equation)

You are studying a population of tobacco hornworms, a type of caterpillar, whose diet consists exclusively of the tobacco plant. Tobacco has the toxin nicotine, which is a chemical defense found in these plants. Individuals of tobacco hornworm within the population vary in their level of resistance to nicotine. Resistant caterpillars can eat tobacco leaves with very few problems.

- Growers don't want their crops to get eaten and so a new variety of tobacco with a much higher dose of nicotine is developed. You want to know if it is possible for these caterpillars to become resistant to this new strain of tobacco with the higher levels of nicotine.

- In your study you catch all of the caterpillars growing on the old variety of tobacco plants (the plants with less nicotine) and measure their resistance to nicotine. Their mean resistance to nicotine is measured as 10 (do not worry about units for this question). You then release them into an experimental field with the new, more toxic variety of tobacco (higher levels of nicotine). You come back one week later and discover the survivors from the original individuals you transplanted have a mean resistance to this new strain of tobacco at 12.

- Next year your plan is to measure the resistance to tobacco in the offspring of your original group of caterpillars. But before you perform this experiment, you want to predict what the response to selection will be to see if resistance to higher levels of nicotine will likely evolve in these caterpillars. Use the relationship of the breeder's equation to answer the following:

1. First, calculate the Selection Differential for this species

2. If Heritability = 0.8; calculate the Response to Selection

3. Do you expect selection to act to increase or decrease resistance to nicotine in the caterpillars if allowed to feed on the plants with higher levels of nicotine? In one sentence explain your reasoning.

- Researchers trying to understand why the tobacco hornworm is resistant to nicotine discovered that the ingestion of nicotine acts a defense for the caterpillar against certain predators, especially wolf spiders. The caterpillars expel the nicotine out of their spiracles (holes on the side of their bodies they use for taking in air for breathing), and the nicotine-laden air they expel is repellent to potential predators. The researchers called this "defensive halitosis".

They also discovered a gene (MsC) that when expressed allowed them to "puff nicotine through their spiracles." When the researchers turned the gene off using an RNA inhibitor (which stops translation during protein synthesis), the caterpillars were more vulnerable to predators.

Below describe how the three conditions of natural selection would result in the increase in frequency of the trait described above in this insect species. List each condition and then explain how each condition applies to the system described in the question.

a. List the first condition of natural selection

b. Describe how this condition is could be met for the organism described above:

c. List the second condition of natural selection

d. Describe how this condition is met for the organism described above

e. List the third condition of natural selection

f. Describe how this condition is met for the organism described above