4. Adult male guppies (Poecilia reticulata) exhibit genetically determined spots

Question

4. Adult male guppies (Poecilia reticulata) exhibit genetically determined spots, while juvenile and adult lemal guppies lack spols. In a study of selection. male and femalé guppies trom genctically diverse populations wer collected from different mountain streams and placed together in an isolated enyionmient containing no predators The study population was maintained for several gencrations in the isolated area before heing separated mto two groups! One group was moved to an artificial pond containing a fish predator. w hile a s cond gi otip via moved to an artificial pond containing no predators. The two groups went through several generations in thein new environments. At different times during the experiment. the mean number of spots per adult male guppy was detcrmined as shown in the figure below. Vertical bars in the figure represent two standard crrors of the mean (SEM). Predator present Predator absent Population Separated : into Groups 20 Time (months (a) Describe the change in genetic variation in the population between 0 and 6 months and provide reasonin b) Propose ONE type of mating behavior that could have resulted in the observed change n the number c) Propose an evolutionary mechanism that explams the change in average number of spots between o and for your description based on the mearis and SEM spots per adult male guppy between 6 and 20 months in the absence of the predator 20 months in the presence of the predator.

Explanation / Answer

From moths 0-6, the genetic variation in the population is decreased. Since, the mean no. of spots increased from 10-12 months and the SEM decreased, which indicates that there was variation in the number of spots and many individual had a number closer to the mean.

One type of mating behaviour that could have resulted in the further incerease in the number of spots in the absence of predator is sexual selection. Perhaps, female guppies showed a preference for males with a greater number of spots and hence guppies with more spots reproduced causing their next generation to have spots ultimately changing the mean no. of spots. This would make having a spot a favourable trait in males and this increase its frequency.

An evolutionary mechanism that would explain the decrease in spots in the presence of predator is natural selection. The spots made the guppiees more visible to the predators, and thus caused them to be eaten more frequently.and didnt had a chance to pass on their genes to the next generation. This would result in a lower frequency of spots.

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