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How eDNA revealed platypus hiding in plain sight

If hide-and-seek was considered a professional sport, the Australian platypus would be an All Star player. Sightings are usually so rare that environmentalists and scientists alike have their work cut out for them trying to prove their existence in any given waterway. But DNA detection technology is now uncovering evidence of their existence on the fringes of major cities, including Sydney, finally giving credibility to years of dubious reported sightings.

The renewed interest in zeroing in on platypus populations has been sparked by concerns of localised extinction in some areas, as well as the endearingly odd-looking creatures being recently reclassified as ‘near threatened’ on the list of endangered species. Which is why researchers at Western Sydney University and the Melbourne University have both recently launched projects to detect them using something called environmental DNA, or eDNA

What is eDNA?

Historically, traditional methods of assessing platypus populations, like trapping for instance, are unreliable and heavily resource-intensive. But eDNA, environmental DNA, is different as it only requires a sample of the water from the creek or river, which can then be sequenced in the laboratory to look for platypus DNA left behind in the water from their skin, hair, faeces or mucous.

The platypus DNA is retained in the water for approximately three days, so a positive result means that one was present in that general location within the previous three days. It means that scientists are able to detect the presence of platypus, or a ‘paddle’ of them in a body of water using DNA without ever having to sight them. By using this technology, the Western Sydney University researchers found evidence of up to eight new sites of platypus habitation on the city's north-western edge in the Cattai River catchment, which includes the suburbs of Rouse Hill, Box Hill, and Kenthurst.

Scientists can undertake two types of DNA detection, either single-species to target a specific species DNA or multi-species sampling, often referred to as metabarcoding. Metabarcoding is possible due to the increasing accessibility of whole genome sequencing, or ‘Next Generation’ sequencing allowing the whole genome to be rapidly sequenced in hours.

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What does it mean for conservation?

As eDNA is fast becoming the preferred method of collecting data on threatened and endangered populations of native animals and fishes, scientists can now paint for the first time the truest picture of the whereabouts of rarely-sighted species.

While it is limited in that it can’t provide specific information on the sex or health status of the indiviual species detected, across large geographic areas it allows them to collate data on where they inhabitate and give better estimates as to -in the case of platypus- their distribution across south-eastern Australia. Over time with continued eDNA surveying, this data will become a powerful tool for conservationists and scientists to use to help preserve Australia’s biodiversity.

Learn how we can survey platypus from just a water sample! This film demonstrates the platypus environmental DNA collection process for citizen scientists.pl...