In one species of cichlid fish, males can have either yellow or red fins that they use in displays to attract mates or defend their territories. In certain populations the relative numbers (or frequency) of males with red vs. yellow fins is different (in some populations red finned individuals are more common but in others the yellow finned morph is more common - but both fin colors are present in each population). In the following activities you will test the hypothesis that the maintenance of both fin colors in populations is due to a type of balancing selection known as negative frequency dependent selection. According to this hypothesis, the fitness of fish with red fins is greater when fewer males have this trait (i.e., when more males have yellow fins). To test this hypothesis, the biologist set up several experimental pools with cichlids in which the frequency of males with red fins was controlled. The biologist then determined the number of offspring that each red male had and recorded the following data

Using the formula for a line (y = mx + b) determine the equation for your model by hand by choosing two points on your line and write it below:

y = 18.3x + 178.3

Now using the equation you came up with, describe in words below how the frequency of male red finned fish in the population influences the fitness of red finned males in that population. Use the exact value of the slope from your model when describing this relationship.

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Observation Number of Red Average Number of {1,} per 100 Offspring per Red Individual Fish {3:} Male [yr]

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