Detoxification of organic compounds by the Malpighian tubules of insects
A project undertaken at the School of Life and Environmental Sciences, Deakin University, and supervised by Stuart Linton
Insects such as fly larvae or maggots live in environments such as rotting fruit and meat which are full of toxic chemicals, but despite this they are able to thrive. What allows this is their remarkable ability to detoxify the chemicals and to get rid of them so that the levels within their bodies are so low that they have no toxic effect. Traditionally the fat body, which is equivalent to our fat and liver, was thought to be the site of detoxification. However the insect kidney’s, called the Malpighian tubules, may also be an important site of detoxification. Furthermore the Malpighian tubules may be involved in getting rid of or excreting the detoxified substances. If this is true then this remarkable organ may have the combined function of our kidneys and liver. The beauty of this system is that the detoxified chemicals may be easier to excrete since the detoxification process may add a “chemical handle” which makes their removal easier. However what “chemical handles” are added and the chemical processes, called enzyme pathways, used to create them are unknown. Also it is unknown how important the Malpighian tubules are in this detoxification process or if this process would lessen the toxic effects. This project will investigate these aims using Malpighian tubules from the fruit fly, Drosophila melanogaster (the lab rat of the insect world) and Australian blow flies (Calliphora species). The larvae of both of these species live respectively in environments of rotting fruit and meat. The smallest physiological preparation known to science, called the Ramsay assay will be used to investigate these aims. A physiological preparation is where a whole organ is removed from an animal, in this case the Malpighian tubules, and set up in a salt solution that mimics the internal environment of the insect. This allows the organ to continue to function and hence it can be studied. Using a model toxic chemical and the Ramsay assay we will identify exactly what “chemical handles” are added and the chemical processes responsible for their production. We will also determine the efficiency of the process and if the process lessens the toxic effects to the animal.
This project will ascribe a new function to the Malpighian tubules. The Malpighian tubules were previously thought to function solely as the insects kidneys and this project will also demonstrate that they may also have a liver function. It will also provide a better understanding of the adaptations that insects possess to allow them to become the most successful animal group in terms of numbers and diversity.