Hormone-toxins to reduce possum fertility
Scientists in New Zealand investigated whether a roundworm parasite could be used to deliver a hormone toxin to possums.
This article looks at the research by scientists at AgResearch. They investigated the use of a hormone-toxin which destroys the cells that produce fertility hormones. The hormone that is used to deliver the toxin to these cells is called Gonadotrophin-Releasing Hormone (GnRH). The toxin, when delivered specifically to cells in the pituitary gland, destroys only those cells and makes possums sterile or less fertile than they would normally be. The toxin would not kill the possum.
Using a hormone-toxin to control possum numbers
Dr Warwick Grant and Dr Doug Eckery are investigating the effects of a toxin (poison) on possum fertility. The toxin affects a hormone called Gonadotropin Releasing Hormone (GnRH). This hormone starts off a cascade of biological reactions needed for a normal reproductive cycle. If this hormone is affected, the possum becomes infertile, or a lot less fertile. This work is still in the research phase, and is being carried out by scientists at AgResearch.
Getting the biocontrol agent to the possums
One way of getting the hormone-toxin to the possum is to use bait. The problem with this method is that the bait needs to be re-distributed over and over. This is expensive.
Find out more about this in the article, Delivering biocontrol agents to possums.
Biocontrol and vectors: What is a vector?
In the case of biological control, it is an organism that carries, or transfers, the control agent to the target organism. For example, in the research into possum biocontrol being carried out at AgResearch, a vector is needed to spread the hormone toxin amongst possums in order to make them infertile.
A natural possum parasite
Another way of spreading the hormone-toxin amongst possums is to use a naturally occurring vector. A vector is a carrier organism.
In this case, the vector could be a roundworm parasite. The scientific name of this parasite is Parastrongyloides trichosuri. It is a little worm that lives in the small intestine of the possum. It is found naturally in possums in the North Island of New Zealand and does not seem to harm the possums.
Parastrongyloides trichosuri: A possum parasite
These roundworms live in the digestive system of possums. They are found naturally in possums in the North Island of New Zealand, and don't appear to harm the possums. Scientists are hoping that they might be able to modify the worms so that possums infected with them become less fertile. This would help to control the number of new possums born in New Zealand each year.
The aim was to genetically modify the nematode worm to produce the hormone-toxin.
Genetically modifying worms to affect possum fertility
At AgResearch, scientists are modifying a parasitic worm that infects possums. The modified worm will be able to seriously reduce the fertility of possums that it infects. Dr. Warwick Grant explains that foreign DNA is injected into the ovaries of a female nematode. The baby nematodes that carry the foreign DNA (the 'transgene') are then selected and used for further research and testing.
If the modified worm that is producing the hormone-toxin infects a possum, it would make possum sterile or at least make it much less fertile than it would normally otherwise be. In other words, the possum would continue to live a normal life, but without having as many babies.
The research
People involved in the project had to investigate several things:
Possum reproduction and how the toxin works
Assessing the suitability of the nematode worm as a vector (carrier) of the toxin
Modifying the nematode worm so that it can produce the toxin and spread it amongst possums
The role of collaboration was important. Different people were able to contribute in different ways to the project.
An update
In a 2011 report, Dr Jan Wright, Parliamentary Commissioner for the Environment wrote that although significant research effort and resources were put into possum contraceptive vaccines and hormone toxins, funding for the projects finished in September 2010. There was concern about the length of time required to produce results, risks associated with the biocontrol agents and potential controversy over genetic engineering.
Nature of science
Most scientific research comes to a natural conclusion. Even if the results appear negative or inconclusive, they help to evaluate current thinking and often answer questions formed as part of the investigation.
