The Rapid Rate of Thermal Adaptation of Drosophila Melanogaster

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Table of Contents

Introduction
Experimental method of testing rapid thermal adaptation in D. melanogaster
Conclusion
Works Cited

Introduction

Background

The abiotic factors of temperature, pressure and humidity play an important role in the ecology of organisms, especially because they have an impact on the survival and reproduction of species. According to Overgaard and Sørensen (159), when temperature, humidity and pressure conditions exceed certain thresholds, the survival of an organism is likely to be impaired, which may reduce their fitness for survival. As such, studies have shown that these factors have played a significant role in the evolution of organisms. In addition, these factors act to influence and direct the evolution of organisms (Overgaard and Sørensen 159). To determine the optimum level and range of these abiotic factors, it is necessary to measure the fitness of various individuals of a single population across a wide range of abiotic factors such as temperature. This makes it possible to measure the fitness of a population (Overgaard and Sørensen 159). Temperature is one of the most important abiotic factors with key roles in the evolution of species.

The fruit fly (Drosophila melanogaster), like most other insects, is an ectotherm, a group of species whose body temperatures follow the ambient temperature. The organism faces difficulties in tolerating an infinite temperature range because its membranes, carbohydrates, proteins and other molecular components assume an unstable state and become degraded when temperatures exceed certain thresholds. This implies that the organism must remain within an environment with suitable temperatures to avoid exceeding the upper or the lower limits. However, D. melanogaster responds to small temperature variations through a number of mechanisms that modify its physiology or behavior. These responses can be acute (immediately after exposure) or chronic (after long-term exposure), which helps in checking the possible impacts of an increase or decrease in the environmental temperatures.

According to Angilletta (67), insects such as the melanogaster respond to the long-term exposure to temperature changes through a phenomenon known as “thermal phenotypic plasticity”. The term refers to the ability of an organism’s genotype to be expressed differently depending on the environmental conditions affecting the organism at a given time and space. The mechanism is believed to have evolved as a way of increasing the organism’s degree of fitness and survival, a hypothesis known as the “beneficial acclimation”. The phenomenon allows the organism to adjust to the permanent or transient environmental changes in their phenotypic rather than genotypic aspects (Angilletta 147). Acclimatization is one of the most significant methods through which the insects use phenotypic plasticity to change their physiology in order to fit into the new environment after the immediate temperatures change significantly. Studies have shown that acclimatization is strongly linked to chronic changes in the environmental conditions, where the temperatures, humidity and pressure change at once (Hoffmann, Sørensen and Loeschcke 176). On the other hand, the change of a single environmental condition such as temperatures alone is known as acclimation, a phenomenon that can only observed under controlled conditions, especially in a laboratory (Overgaard and Sørensen 161). In these conditions, it is possible to hold various environmental conditions constant as a way of isolating the physiological changes resulting from the change of a single environmental factor or interest. In this way, it is possible to observe the specific rate of survival or performance in the organism, which reflects the evolutionary impact of the specific condition. In the proposed study, the specific environmental factor of interest is temperature, a key aspect that plays a significant role in the evolution of insects (Overgaard and Sørensen 161). Drosophila melanogaster and other ectoderms are constantly affected when temperatures in the immediate environment change, but they are able to survive and perform normally due to specific mechanisms that work to ensure that the organism adapts to the changing environment (Overgaard and Sørensen 161).

The study hypothesis

Under natural conditions, the Drosophila melanogaster encounters variations in the environmental temperatures. Several studies have shown that the organism adapt quickly to these variations. Researchers have also shown that this phenomenon is also an evolutionary mechanism that insects have been using to adapt to the changing environment, especially due to the effects of global warming (Hoffmann, Sørensen and Loeschcke 176). Nevertheless, this is debatable and additional studies are necessary to confirm the hypothesis.

The proposed research tests whether beneficial acclimation hypothesis is helping insects such as the D. melanogaster to adapt to the rapidly changing temperature conditions.

Purpose of the study

Therefore, the purpose of the proposed study is to test the above hypothesis, where laboratory investigations will be applied to demonstrate that D. melanogaster and other ectoderms use the rapid beneficial acclimation as a mechanism of adapting quickly to varying temperatures.

Experimental method of testing rapid thermal adaptation in D. melanogaster

The proposed research will be a quantitative study, where the correlation between varying laboratory temperatures and the insect’s heat/cold shock survival will be measured. Populations of D. melanogaster raised in a laboratory will be placed in cages exposed to variations in light and temperatures over a period of 2 days (Hoffmann, Sørensen and Loeschcke 201). The temperatures in the cages will range between 12^OC and 25 ^OC. During the period, the researcher will sample the organisms after every 6 hours, where their ability to survive the heat or cold shock will be measured. This is the organism’s degree of thermal tolerance.

The data collection methods will involve studying the survival rates of the individual insects inside the different cages with different temperatures. The ability to survive heat and cold shocks will be obtained by measuring the degree of performance and survival. In this case, survival rates will be measured by counting the number of the dead individuals and those alive after the two-day period of exposure to extreme conditions. A large number of dead individuals will suggest that the survival rate is minimal. A large number of organisms remaining alive after the period will suggest that the animals have the capacity to withstand the condition, thus supporting the hypothesis (Hoffmann, Sørensen and Loeschcke 196). On the other hand, the performance rate will be obtained through counting the number of animals remaining active or inactive during the exposure to the temperature changes, which will support the hypothesis.

Conclusion

It is expected that the results will show a significant positive correlation between temperature changes and the rates of survival to heat and cold shocks (Angilletta 163). In addition, a significant negative correlation between the two aspects in certain cages is expected. The expected results will be used to show that Drosophila melanogaster constantly adapts to environmental changes, a factor that will be used to explain the importance of physiological mechanisms in adapting to the changing environmental conditions in the modern world (Overgaard and Sørensen 162).

Works Cited

Overgaard, Johannes and Jesper Sørensen. “Rapid thermal adaptation during field temperature variations in Drosophila melanogaster.” Cryobiology 56.2 (2008): 159-162. Print

Hoffmann, Ary A, Jesper Sørensen and Volker Loeschcke. “Adaptation of Drosophila to temperature extremes: bringing together quantitative and molecular approaches.” Journal of Thermal Biology 28.3 (2003): 175-216. Print

Angilletta, Michael James. Thermal adaptation: a theoretical and empirical synthesis. Oxford University Press, 2009. Print

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