Team:Tongji China/Demonstrate
TongJi iGEM
TongJi iGEM
Demonstrate
Here is what we have accomplished with this project
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The Project
Our project aims to control the population of Diptera insects, such as mosquitos, which do harm to human health. Among all the Diptera insects Drosophila melanogaster is the only model creature with well developed protocols to culture and experiment, so we choose it as the chassis to test our design in the project.
It would be great for us to get accurate changes of the whole population in the natural environment to test our system. But, unfortunately, it is almost impossible for us to observe a small group in a specific area due to the lack of equipment and skills. Although Drosophila melanogaster has been regarded as a model creature for a long time, we have found little published data about its population changes.
Therefore, building a population growth model can help us determine the effect of our system when applied to natural environments.
It would be great for us to get accurate changes of the whole population in the natural environment to test our system. But, unfortunately, it is almost impossible for us to observe a small group in a specific area due to the lack of equipment and skills. Although Drosophila melanogaster has been regarded as a model creature for a long time, we have found little published data about its population changes.
Therefore, building a population growth model can help us determine the effect of our system when applied to natural environments.
Model Theory
In 1945, Leslie P H. introduced a mathematical method to predict the age structure and population through time from the age structure of the initial population. Here we use Leslie matrix to make our model better.
Depending on the physiological characteristics of each individual, the maximum life age is divided into M groups. The objective it to find how the age distribution evolves. The time starts from t=0 and evolves in steps (t=0, 1, 2...), and the interval is the same as that of the age group.
Suppose that, at the beginning (t=0), the number of individuals in the I age group was Ni(0), i= 1, 2,... M. so the age distribution vector is:
FORMULA 1
The reproductive rate of the I age group is fi(0) ,i= 1, 2,... M;
The survival rate is Si(>0), i= 1, 2,... m - 1;
Between two periods, there is an iterative relationship between the number of individuals in each age group ni:
FORMULA 2
In matrix form:
FORMULA 3
The following chart shows the differences between the proportions of female flies that can produce normal offspring in two different conditions:
It can be seen that in the case of the small mating rate, the inhibition effect of releasing sterile male flies with male-male courtship is more obvious to reducing population quantity, which is consistent with the purpose of our modeling.
Here we also shows the result when the number of modified fruit flies was five times as large as the wild flies and the mating rate is 0.4, the effect on the final population in 15 days. (The yellow line represents the sterile male flies with male-male courtship, and the purple line represents the sterile male flies)
Depending on the physiological characteristics of each individual, the maximum life age is divided into M groups. The objective it to find how the age distribution evolves. The time starts from t=0 and evolves in steps (t=0, 1, 2...), and the interval is the same as that of the age group.
Suppose that, at the beginning (t=0), the number of individuals in the I age group was Ni(0), i= 1, 2,... M. so the age distribution vector is:
FORMULA 1
The reproductive rate of the I age group is fi(0) ,i= 1, 2,... M;
The survival rate is Si(>0), i= 1, 2,... m - 1;
Between two periods, there is an iterative relationship between the number of individuals in each age group ni:
FORMULA 2
In matrix form:
FORMULA 3
The following chart shows the differences between the proportions of female flies that can produce normal offspring in two different conditions:
It can be seen that in the case of the small mating rate, the inhibition effect of releasing sterile male flies with male-male courtship is more obvious to reducing population quantity, which is consistent with the purpose of our modeling.
Here we also shows the result when the number of modified fruit flies was five times as large as the wild flies and the mating rate is 0.4, the effect on the final population in 15 days. (The yellow line represents the sterile male flies with male-male courtship, and the purple line represents the sterile male flies)
Conclusion
Based on the historical data and experimental observations, we simulated the population change of both modified and wild type Drosophila melanogaster in natural environment. It indicates that the introduction of modified Drosophila into wild populations can indeed control the population of the group even in one or two weeks. These results that it may be a viable and novel population control method.
Future
In the future we are planning to introduce new parts to strengthen the effect by introducing infertile male flies along with the existing male-male courtship features. We can also screen out more Gal80 temperature-dependent variants to make our system work at different temperatures. Furthermore, we are trying to combine the different parts in our system into only one chromosome to enhance the heritability. We sincerely hope that our work will eventually be useful in the real world.
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