Question

Design experiment on microevolution - Microevolution is the change in allele frequencies that occurs over time within a population.

Include 3 parts:

1. Experimental design.

2. Results.

3. Conclusions

Answer 1

Microevolution refers to the relatively quick change in allele frequencies that occur in a population due to the processes of mutation, selection, gene flow, and genetic drift. Microevolution can be observed in the lab via artificial selection experiments, where we manipulate the environmental settings to change the selection pressures on the individuals of a population, thereby changing the fitness of different alleles. Guppies are used as a common study system used to demonstrate artificial selection due to their ease of handling and high reproduction rates. For example, the spots on the guppy are genetically controlled and can be passed on from parents to offspring. These spots help the guppy to blend in better with their environment, thus helping it to avoid predation. Since predation is a selection pressure here, changing the surrounding environment can be expected to vary the fitness of the different spot patterns, either making the guppies carrying them more susceptible to predation, or less susceptible. Eventually those alleles that help make spots more appropriate to blend in with the new environment can be expected to be selected for and get fixed in the population.

Experiment design

This experiment will study the effect of the presence of a predator in the spot coloration of guppies. Guppies naturally exhibit sexual selection for striking coloration in males, but this can make males more susceptible to predation. Four artificial ponds of equal size and characteristics can be set up, differing only in the coarseness of the gravel used to line the bottom. Two will be laden with coarse gravel, and two will be filled with fine gravel. A population of guppies of the same age, with natural variation in the spot sizes can be randomly sorted into four groups (same number of males and females for each pond) and assigned randomly to one of the four pools. Two of these pools will be left as controls where guppies will be reared for generations in the absence of predators. Here, sexual selection will be the only selection pressure at play. In the other two pools, a predator can be introduced, and the guppies can be reared for the same number of generations as in the first two pools (say 20 generations). After the selection period, score the guppies for the size and frequency of the spots on guppies.

Results

The guppies in the control ponds will have spots that put them in contrast with the gravel background, with those in coarse gravel background having numerous small spots and those in the fine gravel background having large dark spots. This would be in contrast with the situation in the pools with predators, where the guppies in the pool with coarse gravel will have large dark spots and the guppies in the pool with fine gravel will have numerous small spots.

Conclusions

In the pools without predation, sexual selection is the dominant selection pressure on the males, and hence, males which stand out from the background better will find it easier to find a mate. Over time, this feedback loop fixes spots which give the males contrast against the background. On the other hand, such a contrast would be detrimental in the presence of a predator, so in the pools were predators were present, selection will favor males whose coloration is more in alignment with the background, as these males are more likely to escape predation and sire progeny.

You can read up on the work of John Endler (1980) to learn more about this experiment.

I hope this helps ?