Natural and Sexual Selection of Vestigial and Wild Type Drosophila Melanogaster

Natural and Sexual Selection of Vestigial and Wild Type Drosophila Melanogaster

Abstract In this experiment, vestigial flies as well as wild type flies were used to create some diversity as well as test one of our hypotheses. Our hypotheses are as follows:

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1. The wild type flies will have a greater relative fitness compared to the vestigial flies based on only sexual selection. The wild type has a relative fitness of 1 since it has fully functional wings. Vestigial Winged flies are not as sexually appealing since their wings are not functional and the wing movement is a vital part of their mating ritual.
2. The vestigial fly will have a greater relative fitness when considering both sexual and natural selection. With the presence of natural selection (flypaper hanging from the top of the cage) posing a larger threat to the wild flies b/c they can fly better, this will allow vestigial flies to prosper better. To set up this experiment, two twenty-five gallon aquariums, 3 Petri-dishes, 200 flies, rotten bananas, and yeast were used. It was decided that there would be 80 vestigial flies and 20 wild type flies to total to an initial population of 100 drosophilas.

In the sexual selection circumstance, the vestigial drosophila’s carrying capacity is somewhere around 80 individuals, which is consistent with the wild type drosophila’s carrying capacity in this circumstance (Figure 4). In the sexual and natural selection circumstance the wild type drosophila has a carrying capacity at approximately 100 individuals (Figure 5). As both of the p-values from each circumstance in our experiment are greater than 0. 05, both hypotheses must be refuted. Introduction This experiment focuses specifically on Drosophila melanogaster, also known as the common fruit fly. For over 100 years scientists have been using them in experiments as they are referred to as a “model organism. ” They were deemed a “model organism” since they are characterized as having a large reproductive capacity, a medium-size, a short generation time, and are inexpensive to keep alive. Fruit flies only consume yeast growing on rotting fruit. Sixty-one percent of human genetic diseases have been found in fruit flies, they also share many similar genes with humans.

The male fruit fly spends most of his time chasing after and singing to female flies with hopes of mating with her, they are successful about once a day. The male fruit fly frequently sticks out one wing or the other which is accompanied by its vibration, producing a “love song” that can be recorded with specialized microphones. To distinguish male drosophila from females, there must be a distinctive black spot on the distal end of their abdomen for it to be a male, the females do not have this black spot. In this experiment, vestigial flies as well as wild type flies were used to create some diversity as well as test one of our hypotheses. Vestigial flies do not have well-functioning wings, however, wild flies do have functioning wings. Within this experiment, degrees of natural selection, sexual selection, and a combination of both were tested on the two types of flies. Natural selection is the survival of the fittest. Sexual selection is the ability of organisms to choose their mates depending on their species. Relative fitness is the ability of an organism and species to survive and produce fertile, successful offspring.

The purpose of our experiment is to determine the effect of natural selection on two subspecies coexisting under similar circumstances. Our hypotheses are as follows:

1. The wild type flies will have a greater relative fitness compared to the vestigial flies based on only sexual selection. The wild type has a relative fitness of 1 since it has fully functional wings. Vestigial Winged flies are not as sexually appealing since their wings are not functional and the wing movement is a vital part of their mating ritual.
2. The vestigial fly will have a greater relative fitness when considering both sexual and natural selection.

With the presence of natural selection (flypaper hanging from the top of the cage) posing a larger threat to the wild flies b/c they can fly better, this will allow vestigial flies to prosper better. Materials and Methods To set up this experiment, two twenty-five gallon aquariums, 3 Petri-dishes, 200 flies, rotten bananas, and yeast were used. The bananas are chosen to be an accelerant for the growth of the yeast and were frozen so they would be easier to cut. The yeast was used because the drosophila melanogaster prefers this as a food source. The vestigial and wild type flies were sexed (to determine their sex), sorted, and counted. An initial population size of 100 total flies was decided so that it would be easier to determine the phenotypic percentage of the total population. Flypaper was placed in one of the sets of cages to impose a method of natural selection as well as the sexual selection which is being sorely tested by the other set of cages. It was decided that there would be 80 vestigial flies and 20 wild type flies to total to an initial population of 100 drosophilas.

Next, the flies were anesthetized flies using Fly Nap. The flies were counted out to reach the desired ratio, sexing the flies making sure there are equal amounts of males and females to be sure there are ample individuals to allow successful mating. The fly’s food was prepared by taking a frozen rotten banana, cutting it in half, mashing up the banana meat, and mixing yeast into it. The bananas were then cut into halves horizontally (six halves total in each cage) and split down the middle lengthwise leaving the peel on the banana, revealing the yeast-banana mush and placed into the Petri dishes. The Petri dishes were then arranged into a horseshoe shape in the bottom of the aquarium. Next, the allele frequencies were determined by using the Hardy Weinberg equation (p2+2pq+q2). This experiment will prove our hypotheses sufficiently if carried out correctly by changing the total populations of the subspecies of each fly. Since the vestigial flies do not fly they will be affected by sexual selection only. However, the wild type flies will be affected by sexual and natural selection.

Next, the p-values of each set of data were calculated by using the ‘ANOVA: Single-factor’ function in Microsoft Excel. The p-value of the sexual selection only set of data came out to be 0. 097, or 9. 7% that our null hypothesis that the vestigial flies would be more fit than the wild type flies would come true. In Table 4, it is shown that the calculated p-value for the sexual and natural selection conditions of the vestigial and wild type flies produced a value of 0. 1 or 51% that our null hypothesis would come true. Figure 2 shows the data collected in the sexual selection circumstance of both the vestigial and wild type drosophila as well as the total population as to compare visually the drastic contrast between the two subspecies. The wild type flies remain more successful than the vestigial flies.

Figure 1: In this figure, it is shown visually the differences in the numbers of flies counted per each subspecies of drosophila while under only sexual selection conditions. Figure 3 shows the Natural and sexual selection circumstance’s effects on the populations of both vestigial and wild type flies as well as the total number of flies in the enclosure. The Vestigial flies start off more prosperous than the wild type flies, but then the wild type drosophila regains their success and start reproducing at incredible rates.

Figure 2: In this figure, it is shown visually the differences in the numbers of flies counted per each subspecies of drosophila while under both natural and sexual selection.

Figure 3:  Shows the Natural and sexual selection circumstance’s effects on the populations of both vestigial and wild type flies as well as the total number of flies in the enclosure. The Vestigial flies start off more prosperous than the wild type flies, but then the wild type drosophila regains their success and start reproducing at incredible rates.

Figure 4: In this figure, the relative fitness and carrying capacity of each subspecies are shown. Figures 4 and 5 have been included to compare fitness levels of each of the fly subspecies. The scale on the y-axis has been multiplied by 10 to better understand the incredible contrast between the species. In both circumstances, the vestigial drosophila starts out with a higher relative fitness then reaches an equilibrium level with the wild type flies and they switch dominance of their relative fitness.

Figure 5: In this figure, the relative fitness and carrying capacity of each subspecies are shown. Discussion This curvature of the graphs and intersections happen because when the subspecies reach their carrying capacities, they must make a change so that they can survive as a community. In the sexual selection circumstance, the vestigial drosophila’s carrying capacity is somewhere around 80 individuals, which is consistent with the wild type drosophila’s carrying capacity in this circumstance (Figure 4). In the sexual and natural selection circumstance the wild type, drosophila has a carrying capacity of approximately 100 individuals (Figure 5). As both of the p-values from each circumstance in our experiment are greater than 0. 05, both hypotheses must be refuted. It is suggested that this experiment is conducted again using a better enclosure for the flies. During the semester, countless flies were flying around the lab which could account for the numbers of flies being inaccurate. There are possible errors in the sexing as well as the counting of the flies.

Only a few flies crawled into the tubes with apple cider vinegar and didn’t allow for every flight to be accounted for. The temperature of the lab was often quite cold, therefore this could account for some of the flies dying. As the temperature was not a factor we were testing in this experiment, the temperature should be kept at a constant level. This experiment is important on a global level because of the closeness in the similarities of the genes between the drosophila and humans. This experiment shows us how, if humans were meant to survive strictly on natural and sexual selection, that mutations would play a part in the selection of mates.

Reference

1. Hall, Jeffrey C. Jun 1994.
2. The Mating of a Fly. Science 264 No. 5166: pp 1702-1714. Lynch, M., J. Blanchard, Houle, D., T. Kubota, Shultz, S., L. Vassilieva, Willis, J. Perspective: Spontaneous Deleterious Mutation. Evolution 53 No. 3: pp 645-663. Stowe, K. A., L. L. Hester, and Vieyra, M. L. 2008.
3. Biology 101 Lab Manual. Hayden- McNeil Publishing Inc. , Plymouth, Michigan, USA.

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