News: eDNA
Why it’s revolutionising conservation
It was the story that captured the nation’s imagination. Last year, an international group of scientists, nicknamed the Super Natural History team, had come closer to solving one of the most enduring mysteries the world has ever known – does Nessie exist?
For decades, there have been reported sightings of a monstrous creature lurking in Loch Ness. But the enigmatic beast has always avoided detection, despite a number of serious investigations using the likes of submarines and sonar. In 2018, a team led by Professor Neil Gemmell, from the University of Otago in New Zealand, spent several weeks on the Scottish loch collecting bucketloads of water, which were hauled back to a lab for testing. What the researchers hoped to find in these samples were telltale traces left by the wildlife living in the loch – in the form of so-called ‘environmental DNA’.
Traditionally, scientists have kept track of species using monitoring methods such as catching and tagging, or camera traps. But techniques like these are often time
eDNA has been used to survey the poster child of British conservation – the great crested newt.
consuming, expensive and don’t necessarily yield accurate results. It can be pot luck if a snow leopard passes in front of a camera on a vast mountainside, or if a whale shark comes within tagging distance out at sea. Environmental DNA (eDNA) looks set to be a game changer for conservation. As an animal passes through a particular environment – whether that’s swimming through a body of water or walking over soil or snow, it leaves traces of its existence, such as shed skin cells, mucus, urine and faeces. As DNA can be extracted from the tiniest sample of organic tissue, these cells can provide enough information for scientists to determine details about the organism. Hence, the phrase ‘environmental DNA’, as it is sourced from the environment that the creature has passed through.
By comparing the eDNA collected from Loch Ness with the profiles of known species, Prof Gemmell and his team were able to identify what species do exist in the loch, and which ones don’t. Predictably – but perhaps sadly – no traces of a monster were found, nor any DNA from potential Nessie contenders: catfish, sturgeons or sharks. The most likely culprits seem to be giant eels – unless Nessie managed to hoodwink the scientists.
Local conservation
In recent years, environmental DNA analysis has been used to survey the poster child of British conservation – the great crested newt. These elusive amphibians have been gradually declining in Britain and Europe, mainly due to a decrease in ponds and breeding grounds. Over the years, they have become the scourge of the building industry – developments that risk disturbing them can only go ahead if the newts can be transferred to another suitable habitat. Monitoring their presence has thus become big business.
Since they are nocturnal creatures, counting newts has traditionally involved a night-time vigil. But the advent of eDNA analysis means that sampling can be done
in the daytime, with fewer ecologists and resources required to accurately monitor the populations.
Further afield, eDNA analysis is also revolutionising conservation projects in remote regions around the world. Scientists working with WWF Alaska and the Department of Wildlife Management have been tracking polar bears by gathering samples of fur from footprints in the snow. By analysing the eDNA in these samples, the scientists are able to identify individual bears and have started to map out family trees. Collecting samples in this way is far less intrusive than the traditional method of fitting a tracking collar, and gives a more accurate picture of population size.
Likewise, in the Caribbean – where shark surveys previously involved donning your scuba kit, dunking cameras overboard or setting fishing lines to catch and tag sharks – eDNA analysis is having impressive results. A 2017 study at Florida International University showed that sharks are thriving in areas of the ocean where commercial fishing has been banned, such as the Bahamas, but inevitably struggling in the less-well-protected waters around Jamaica and Belize. In another study in New Caledonia, more shark species were identified in two weeks of water sample collection for eDNA analysis than in two years’ worth of scuba dives and underwater filming expeditions.
A wider perspective
As eDNA sampling is relatively quick and easy, it can paint an accurate portrait of an ecosystem as a whole. That was the case in a study carried out around one of the main rivers in the northern Peruvian Amazon.
WWF Peru collected samples at 40 points and sent them to NatureMetrics, a specialist eDNA company in the UK, for analysis.
“The rain had washed DNA from the land into the water, creating a ‘soup’ of DNA,” says CEO Kat Bruce. “In the samples, we found traces of more than 600 vertebrate species, which included a lot of fish, but also a huge variety of terrestrial vertebrate fauna, such as jaguars, giant anteaters, bats and night monkeys.” ( see case study, below).
eDNA can give a heads-up about alien invaders as well. Take the case of the tilapia. The fish was first discovered in a town in northern Australia in 1978, but now rules in 20 coastal areas. It’s such a pest that the fine for keeping one as a pet is up to AUS$200,000, in case it escapes. But it can be hard to calculate population size if there aren’t yet many around. The key is to catch an invader early, and roll out control measures before numbers get too high – which is what happened in the UK with invading zebra mussels blocking water treatment plant pipes, and Chinese mitten crabs crumbling riverbanks with their burrows. If eDNA sampling had been