Reference no: EM132899530

Introduction:

Darwin (1871) defined sexual selection as selection on those traits specifically involved with acquiring mates. Examples of sexually selected traits include bright, conspicuous colouration (e.g., a greater bird of paradise's tail) to attract mates, or weaponry in males (e.g.,antlers of red deer) to battle other males for access to females. Traits that convey a sexual selection advantage are often counterbalanced bynatural selection. For example, African widowbird males have long tails that are attractive to females (Andersson 1982). However, while females prefer males with experimentally lengthened tails, these males suffered a higher risk of predation (Andersson 1982).

In this practical, we will use a model to simulate a classic experiment on the balance of sexual selection and natural selection in guppies (Endler 1980). Guppies are small freshwater fish from the Caribbean islands and South America. They are sexually dimorphic: males are smaller thanfemales, but have larger tails and fins. In Trinidad, they live in small pools associated with mountain streams, some of which have guppy predators (e.g., the pike cichlid and Rivulus species), while others do not. Why?Endler (1980) found that females prefer to mate with "flashy" males, those with more orange spots on their tail. However, the flashier males may also be more conspicuous to predators and hence be more likely to be eaten. Thus, there are conflicting selective pressures on male guppies.

By the end of this practical, you should be able to:
• explain how sexual selection is directional for a particular trait;
• discuss how female mate choice affectsmale phenotypic variation;
• discuss the balance between sexual selection and natural selection, and how this mayconstrain the evolution of traits.

Modelling the Trade-Off between Natural Selection and Sexual Selection in Endler's Guppies

At the top of the screen, move the "speed" slider all the way to the right (increases the speed of the run).

Set the Run_Time to about 5000 (otherwise the simulations take a long time to complete.

Question 1. Systematically test the effects of changing each of the different Control variables ONE AT A TIME. Make sure that all other Control variables remain at their default values as you are testing each variable.For EACHReporter variable, you need to report the values for the different reporters at BOTH the start and the end of each run (e.g., in table form as shown below), AND present the graphs at the END of each run. That is, you need to report on modifying 10 different Control variables (the Run_Time Control variable is excluded as you have been instructed to set that to 5000 for all simulations).

Question 2. Once you have explored each of the variables, design an experiment to test the effects of a single predator on male guppy colouration. Hint: Endler (1980) describes one of the predators as being more dangerous than the other. Read the section "Experimental Design: Greenhouse experiment" to determine which predator you should use in your simulation. State your hypothesis and then test your idea. Note the controls you change, and the reporters and both the start and end of the run. Do your results support your hypothesis?

Question 3. Now design an experiment to test the effects of female mate choice on male guppy colouration in the absence of predation. State your hypothesis and then test your idea. Note the controls you change, and the reporters and both the start and end of the run. Do your results support your hypothesis?

Question 4. Now design an experiment to test the trade-off between natural selection and sexual selection on male guppy colouration. State your hypothesis and then test your idea. Note the controls you change, and the reporters and both the start and end of the run. Do your results support your hypothesis?

Attachment:- Sexual Selection.rar