eDNA latest tool in fight against invasive species

The New Zealand mud snail is a small but hardy creature that can reproduce at epic rates. Dispersed across the globe on the waves of globalisation, populations of this tiny aquatic mollusc are crowding out native species in riverbeds around the world.

In 2021 a team of scientists from the University of Iowa, US, deployed innovative eDNA detection techniques to identify water courses where the snail may be hiding unseen, which should allow them to identify the scale of the problem and deploy early interventions to keep populations in check before they do visible, irreversible damage.

eDNA refers to environmental DNA, the genetic material found in skin cells and bodily excretions that are dispersed in local water systems. A single sample of water may contain the genetic echoes of an entire community, providing a powerful window into the ecology of aquatic ecosystems. Detecting these genetic ‘fingerprints’ can enable scientists to monitor rare or threatened species and detect invaders like the mud snail.

“eDNA has been used successfully with other aquatic organisms, but this is the first time it’s been applied to detect a new invasive population of these snails, which are a destructive invasive species in fresh waters around the world,” says Maurine Neiman, associate professor in the Department of Biology and the study’s co-author.

As described in a paper in the journal Biological Invasions, the team searched for the mud snails in eight sites across six rivers in the Susquehanna River watershed, Pennsylvania, which feeds into Chesapeake Bay and the Mid-Atlantic watershed.

Based on eDNA found in the samples, the team confirmed the presence of the snails in one site where none had previously been detected, and found there was a high chance of their presence in all other sites tested. The results confirmed their concerns that the snail had been silently colonising waterways along the Eastern Seaboard.

“eDNA can be used to find organisms at really early stages of invasion, so it can detect a population even when there are so few of the organisms that traditional methods would never find them,” says Neiman.

“This study presents an important step forward in demonstrating that eDNA can be successfully applied to detect new P. antipodarum invasions, and will allow us to more accurately track and potentially halt ongoing range expansion of this destructive invasive species,” writes the study’s corresponding author James Woodell, a research support technician at University of Hawaii at Mānoa.

The eDNA detection technique was developed less than a decade ago, and has been used successfully in all sorts of biodiversity interventions, including identifying faecal contamination in surface water, tracking invasive species like the American bull-frog, and monitoring threatened amphibians.

In the 2019 SCINEMA International Science Film Festival short documentary, Tracking Snow, we join two scientists as they re-purpose the technique of studying eDNA in waterways in order to revolutionise how we study threatened and endangered species living in snow-covered landscapes.

A collaborative meeting of geneticists and carnivore researchers resulted in the proposition that snow tracks are basically water samples if you melt them down. The breakthrough idea highlights the importance of collaboration in conservation.

Instead of the more labour-intensive collection of scat and hair samples, or a reliance on camera traps that often aren’t clear or definitive, the researchers can now easily detect lynx eDNA from their snow tracks.

And because you don’t have to actually see the animals to know that they’re there, this technique allows us to make better informed lynx conservation decisions.

More reading:

• Tracking animals without seeing them
• Scientists go fishing for fish DNA
• Hunting for Loch Ness monster DNA