Selection in Natural Population

Document Type:Lab Report

Subject Area:Biology

Document 1

After the examination of the 36 different galls, it was established that the size of the gall does not necessarily determine the mortality in a significant manner which therefore proves the initial hypothesis wrong. However, other causes of the mortality among the gall flies were discussed which established that the competition for resources, predators, the climate as well as the goldenrod is the main cause of mortality among the gall flies larvae. Introduction Natural selection is one of the basic evolution mechanism alongside migration, migration as well as genetic drift. The grand idea of natural evolution has coined by Darwin is simple but has been misunderstood by many people. In essence, natural selection can cause microevolution which in this case affect the frequencies of alleles.

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At the start of the study, it was hypothesized that the mortality of the larvae was significantly affected by the size of the gall where the larger galls would have the highest chances of larvae survival and vice versa. In this case, the survival of larva was directly proportional to the size of the gall. The main sources of gall fly mortality include the parasitoid wasps, beetles, and the interaction of plant with other larvae as well as the avian predators (Cane and Kurczewski 1976). Nonetheless, there are other causes of larvae mortality which include the human disturbances and the climatic change even though these two factors were taken into consideration in the original hypothesis but they will be discussed. Methods During the study, a goldenrod which contained gall flies was collected and care was taken to ensure that the stem of the plant which contained the gall fly was alive.

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Figure 1. Calliper used to measure the gall After the completion of the necessary measurements, the results were recorded on the paper after which the gall was cut parallel to the stem. During the cutting, the blade was twisted to crack open the gall and expose the internal parts of the gall. After the opening of the gall, the inside of the gall was examined to help in determining if the gall fly survived any attack. Since it was not easy to determine the fate of the gall fly, an important resource referred to as the Solid ago Eurostar Gall was used. This is shown in figure 2 below. This revelation, however, indicates that there are other factors that may be affecting the mortality rate of the larvae of gall fly rather than the size of the gall.

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Figure 2. Mortality of gall fly compared to the gall size Discussion Based on the results of the experiment, it shows that the initial hypothesis of the study was wrong since it indicated that the size of the gall did not affect the mortality rate of the gall larvae. In this case, some of the examined galls indicated the presence of other insects which were not targeted in the study which include the Moderllistena convicta which is type of beetle as well as the Eurytoma gigantea, which is a type of wasp while other galls had some holes which is a clear indication that the galls had been invested with the avian predators. In as much as they do not cause feed on the gall fly, they increase the chances of mortality in the sense that they create tunnels on the galls which exposes the larvae to extreme conditions thus causing their death.

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This issue was noted in the three cases of the galls that were examined during the experiment. The avian predators are also not affected by the size of the gall but instead, some species which include Picoides pubescents and commonly referred to as Downy woodpecker and well as the Parus atricapillus which are commonly referred to as Black-capped chickadees (Dorken and Pieper 2016). These birds are known from making holes in the stem of the galls of the goldenrods and extract the larvae thus increasing the mortality rate. Furthermore, it is evident that the climatic condition of the region plays a significant role in determining the mortality rate of the gall flies. This is because the hypothesis generalizes the mortality as being affected by the size of the gall.

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