Question

Imagine that you are studying a species of guppy in which mature males are observed to have bright orange tails, while females and immature fish have grey tails. You decide to test whether sexual selection can explain this dimorphism.

a) Describe an experiment to test this hypothesis. Include details about what you will measure. Draw and label two diagrams: one showing potential data that would refute your hypothesis, the other showing potential data that would support it.

b) A competing colleague discovers that some mature males in this population have grey tails, and publishes a paper claiming that this evidence shows that sexual selection could not explain the dimorphism in tail color in this species. Do you agree or disagree? What observations or experiments could help you refute your colleague’s conclusion?

----You are allowed to use any sources you like. Make sure to cite any sources you use (any reasonable citation style is fine). Do not copy text from any source (short, cited quotes OK).

Answer 1

Ans.

a) Experiment -

To test whether the presence of bright orange tails in mature males, and grey tails in females and immature fish, can be explained by sexual selection or not, following experiment could be done -

take some mature female fish in 5 tanks as follows -

Tank 1 - place a transparent jar in the middle of the tank having males with bright orange tails.

Tank 2 - place a transparent jar in the middle of the tank having immature fish having grey tails.

Tank 3- place a transparent jar in the middle of the tank having a model with bright orange tails.

Tank 4- place a transparent jar in the middle of the tank having a model with grey tails.

Tank 5 - place a transparent jar in the middle of the tank having only water.

observe the frequency of approach by the females towards the jar containing male fishes / male models/ or just water, over a period of time. show the data in the form of bar graphs and plot the standard error.

data that would refute the hypothesis? that "presence of bright orange tails in mature males, and  grey tails in females and immature fish, is due to sexual selection?" would show almost equal frequency of approach in tanks 1 - 4 (this could be confirmed by student's t - test).

data that would support the hypothesis will show a significant difference in the frequency of approaches between tanks 1/3 and tanks 2/4, as follows -

Ans b)

Having some mature mails with grey tails in the population alone is not sufficient to refuse the role of sexual selection in the differences in the colour patterns observed in majority of the population.

so i don't agree with my colleague and the presence of some mature mails with grey tails in the population could be explained by presence of a mutation in those males in the gene encoding the bright ornage tails such that they cannot produce bright orange colored tails.

conclusions made by my colleague can be refuted by, placing the mature mails with grey tails, in the jar as described in the above experiments. the results would show a significant difference in the frequency of approach as compared to the jar with bright orange colored males.