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Mate Choice in Guppies (Poeciliasp.)

Objectives:

Considering what you have learned in lecture and what you will learn in today’s laboratory session, you should be able to:

1) explain the differences between natural selection and sexual selection.

2) define intersexual selection and intrasexual selection.

3) formulate predictions for today’s experiment regarding mate choice in guppies

4) design an experiment to test behavior

5) interpret and perform a Chi-square test based on your class data.

Introduction:

Sexual selection is defined as differences in reproductive success caused by competition over mates and related to the expression of a trait (Andersson 1994). In typical mating situations in the animal kingdom, there are two components of sexual selection: 1) male-male competition and 2) female mate choice. Sexual selection is the mechanism that influences secondary sex characteristics; traits that are not directly involved in copulation, but typically increase success in an individual obtaining mating opportunities. Some examples of characters that are favored by intersexual selection (e.g., male-male competition) include extreme male body size in elephant seals and large antler size in male red deer (Andersson 1994). These characters are used in dominance interactions between males that can affect the male's reproductive success. Some examples of characters favored by intrasexual selection (e.g., female choice of males) include extremely long tails in male widowbirds and female preference for male calls in tungara frogs (Andersson 1994). These secondary sex traits may be used by males to attract females and obtain mating opportunities.

Today we will perform experiments testing the idea of mate choice with a species of the Poeciliad family; Poecilia sp. (store bought guppies).

Experiment: Mate Choice

*Prediction: Make a prediction based on the information above. Include this prediction in your notebook.

Protocol: (Work in groups of four if possible)

Set-up: 1) Place 1 bright male guppy and 1 dull male guppy in each of the small, outer tanks. It is up to you to determine what is “bright” and “dull”. Draw these males in your notebook! When selecting males, try to match the size of males.

Trials: 2) Place 1 female guppy in the middle of the tank, allow her to acclimate for 5 minutes. 3) For a 10-minute trial record female preference and activity level. To measure female preference you will use two stopwatches to time which side of the tank the female is on. That is, when the female enters a “preference zone” for a particular male (fig. 1) start the stopwatch for that side. Stop the watch when the female leaves that side. The stopwatches will accumulate the total time the female spends in each of the two male preference zones for the 10-minute trial. The male with which the female spends the majority of her time we will call the “preferred male” and is rated a value of 1, while the non-preferred male is rated a value of 0. Also during a 10-minute trial record the female activity level by having a group member count how many times the female crosses the center-line of the tank. 4) After the 10-minute trial remove the female and replace with a new female. 5) Repeat experiment two more times, each time with a different female but with the same two males. However, you must switch the two side tanks, that is, switch the position of the bright and dull males. Each student should put a datatable in their notebook including for all three trials each female’s preference and activity level. You should also record your general observations in your notebook about your group’s experiment including the size of the female (a good estimate will be fine), describe the behaviors of the fish and health/condition of the fish.

When all groups have finished their trials, you will have a second data table of the class data in your notebook. You will also conduct a Chi-square test on the class data to determine the statistical significance of our class data (see additional handout). You will also graph both the class data and your group data for your electronic portfolio. Finally, answer the questions at the end of the lab write-up in your notebook.

Team Member Roles (rotate these for each female tested):

1) One member records the “choice” of the female. That is, record with the stopwatches time the female guppy spends within the choice zone of each male.

2) One member records the “activity levels” of the female. That is, record the number of times the female crosses the center-line of the tank.

3) Other members get fish, record data, keeps track of time of experiment (5 minute acclimation, 10 minute trial), record class data, and responsibilities as described and/or needed.

Figure 1

Experimental Apparatus:

Questions:

1) Why did you try and match the size of the males in the small tanks?

2) Why did you randomize the sides of the large tank the bright and dull males were placed?

3) What conclusions can be drawn from your group data; from class data?

4) Does the experiment from the class data support your prediction?

5) Explain potential sources of error (besides saying “we didn’t do the experiment correctly”)?

References:

Andersson, M. 1994. Sexual Selection. Princeton University Press, Princeton.