Guts and genes – the key to possum eradication?

If you had told 10-year-old me that I would grow up to study the best way to kill animals, I would never have believed you. I loved animals then, and I still do. However, we live in New Zealand, a country with some of the most unique and spectacular flora and fauna out there (although perhaps I am a little biased). With our unique native birds, reptiles, and insects, comes the need to protect them. Many are endangered and need our help so that they will be around for future generations. Unfortunately, this means killing animals.

The biggest hurdles to jump in protecting these species are pests. Almost all land mammals in New Zealand are introduced (the exception being 2 living native species of bat). The introduction of mammalian pests caused 59 species of birds in New Zealand to go extinct, with many more currently on the brink.

One of the largest contributors to this problem is the brushtail possum, Trichosurus vulpecula, a protected species in their native Australia, but an animal New Zealand would be much happier without. They compete with our birds for habitat and food. They rob nests of chicks and eggs. The carry disease to our cows. It is easy to understand our desire to get rid of them. But how do we do that?

Kea, Mountain Parrot, Cheeky, New Zealand, Highlands
The kea, their nests, are a common target of possums (Photo Credit: Creative commons, Bernd Hildebrandt, https://pixabay.com/images/id-2138420/)

New Zealand’s current approach is traps and poison. Department of Conservation (DOC) and other conservation groups are regularly putting out new pesticides and traps in New Zealand bush to reduce possum numbers. It is hard work. One of their more commonly used pesticides and the most controversial is sodium fluoroacetate, or 1080 as most people would know it. Poisons are aerially dropped in large amounts regularly, into regions that are too difficult to access on foot.

Possums in New Zealand have been treated with 1080 for yonks (widespread since 1957). And with constant exposure to a drug comes resistance. Resistance is when there is a decrease in response to a drug (in this case pesticides), usually due to prolonged exposure or genetic mutation.

Researchers at Lincoln University and the University of Johannesburg are trying to find out how resistant our possums are to poisons after decades of exposure. This was done by taking sections of the possum liver and brain and mapping the genes that were present and, more importantly, functioning at high rates. By doing this, they were able to determine the differences in core metabolic pathways, such as cell respiration and energy production, and pathways related to resistance, present in each region and compare them to their overseas cousins and similar species.

What they found was both interesting and unfortunate. New Zealand’s isolated population of brushtail possums have potentially begun to develop toxin resistance. Within the liver, proteins with an 88% similarity to drug-resistant proteins, also found in wombats, were discovered. This is something not present in the Australian-based possums.

There was also a high level of genetic variation within the metabolic pathways being investigated. This means that a lot of the pathways were different from each other. When this happens, it is more difficult for the poisons to be as effective, as the pathway they are designed to break down is not the same every time. Evidence of toxin tolerance was also found within the brain gene samples. This means that our furry friends are getting better at dealing with poisons, although maybe not fast enough to help them. Ultimately, this may be bad news for New Zealand’s native animals.

This research demonstrates that the New Zealand possums are genetically changing due to their environment, and gives us an insight into how. This knowledge will allow us to develop new strategies in order to achieve predator-free 2050. The technology here could also be used to identify unique pathways that could be targeted by a new pesticide, potentially eliminating the risk posed by 1080 to our native birds and domestic animals, although that is likely a while off yet.

While killing animals may not be the most palatable way to deal with the pest problem, research like this will allow the development of a far more painless and specific experience, which is the kindest thing to do.

This article was prepared by postgraduate student Lexi Hunter as part of the ECOL 608 Research Methods in Ecology course.

Emami-Khoyi, A.; Parbhu, S.P.; Ross, J.G.; Murphy, E.C.; Bothwell, J.; Monsanto, D.M.; Vuuren, B.J.v.; Teske, P.R.; Paterson, A.M. De Novo Transcriptome Assembly and Annotation of Liver and Brain Tissues of Common Brushtail Possums (Trichosurus vulpecula) in New Zealand: Transcriptome Diversity after Decades of Population Control. Genes 2020, 11, 436. https://doi.org/10.3390/genes11040436

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