When I was a child, I was fixated on animals. In fact, 5-year-old me would go around telling all the primary school mums that I wanted to be a Palaeontologist. This was often met with some strange looks, quite possibly because they didn’t even know what a Palaeontologist was themselves. Since then, I have been less focused on digging up dead animals and more interested in protecting the ones that are still alive.
In New Zealand, tourism and agriculture are arguably the biggest money-maker industries. People flood from overseas to check out the clean green image being advertised in their home countries for themselves. The ‘Great Walks’ lead tourists through the rugged bush that New Zealand has to offer. Along the way they might even see some of our diverse flora and fauna, of which most can not be found elsewhere on Earth.
On the other hand, the dairy, sheep and beef industries in New Zealand, earn large amounts of overseas revenue. This all started when Samuel Marsden introduced shorthorn dairy cattle to New Zealand from New South Wales and the rest is history.
This brings me to the devious, but very cute looking, Brushtail Possum, Trichosurus vulpecula. In Australia, the Brushtail Possum is a protected species. In New Zealand they are a serious threat to our homegrown species. Possums compete with our native bird species for food and inhabit the same areas. These fluff balls are omnivores. In addition to eating the leaves off trees, they rob the nests of birds and eat the chicks and eggs.
Bovine tuberculosis is a disease that affects many farm animal species. Possums are the biggest carriers of tuberculosis and can infect herds of dairy cows, causing serious illness to the animals and a large vet bill for the farmer. Due to these factors, New Zealand tries incredibly hard to get rid of these furry mammals. One important thing that we need to know is where these possums are present and and in what numbers. For a nocturnal and relatively cryptid species, this is a lot harder to do than simply call a roll!
The use of trace DNA to monitor animals, such as possums, is a relatively new concept. However, a trial was held in Canterbury where researchers collected DNA from saliva left on WaxTags and Chewcards to determine the number of possums in an area and check whether these individuals were Tuberculosis carriers. From the initial field study, it was found that multiple possums would bite the WaxTag and Chew cards which made it difficult for the lab team to isolate certain animals. A new device to collect data was needed.
A mechanical collection device was created which would remove the bait after one animal had bitten into it, which protected the saliva and therefore the individual DNA could be distinguished. The device was a bit like a fishing line, catching its prey and then reeling in the DNA! Researchers found that the mechanical device allowed the DNA to be collected and more easily sequenced. They also found that the genetic material was more easily recovered from covered WaxTags than on the uncovered WaxTags.
Cameras used in the field trials picked up that the possums interacted with the new WaxTags, and 87% of the devices were triggered after the first interaction. This is a positive point because in order for a monitoring device to be useful, the target has to interact with it.
This new way of collecting trace DNA samples was a success. DNA from Brushtail Possums was able to be amplified for genetic identification and was able to detect if diseases were present. The combination of the device being interesting enough for the targets to interact with, and the subsequent DNA extracted being protected until collection, means that it is ever more likely that technology like this can be used for other pest species to determine their disease risk.
The current study is the first to collect trace amounts of possum DNA and keep it protected from the elements until genetic analysis has taken place. This is a pretty big step for DNA collection methods. However, transmission of infectious diseases by vectors, such as possums, is density dependant. More collection devices need to be installed in these areas being studied to create ‘encounter’ history for individuals to determine population density and to calculate the likeliness for for transmission of these vector carried diseases.
This research suggests that there are new ways for non-invasive monitoring pest populations. The road to New Zealand being predator free by 2050 is a long one, but is shortened by the impressive new technologies being developed in the pest management space. This technology is key for determining the populations of pests in their area and how likely their livestock are to contracting devastating diseases such as Bovine Tuberculosis.
Dealing with pests may not be the most fun thing to do week to week, however, determining where populations are and where the risks lie can help experienced personal to more effectively manage pest populations and get New Zealand back to where we should be, mammal predator free.
This article was prepared by postgraduate student Rebecca Anderson as part of the ECOL608 Research Methods in Ecology course.
Emami-Khoyi A, Agnew TW, Adair MG, Murphy EC, Benmazouz I, Monsanto DM, Parbhu SP, Main DC, Le Roux R, Golla TR, Schnelle C, Alizadeh H, Csányi S, Heltai M, Jansen van Vuuren B, Paterson AM, Teske PR and Ross JG (2021) A New Non-invasive Method for Collecting DNA From Small Mammals in the Field, and Its Application in Simultaneous Vector and Disease Monitoring in Brushtail Possums. Front. Environ. Sci. 9:701033. https://doi.org/10.3389/fenvs.2021.701033