DNA from cup of pond water can reveal lot: Kat Stewart will find out with Vidi grant from NWO

She has had the idea for seven years, but now environmental scientist and conservation biologist Kat Stewart finally gets to work on it. She has been awarded a Vidi grant by NWO to find out how DNA from water can be used to shed light on invasive species and their impact on native populations.

In the lecture hall where she has just been teaching students, Kat Stewart conveys her enthusiasm for environmental DNA (‘eDNA’), via Teams. ‘It’s just a really cool discovery. All organisms live in a genetic soup – even as I sit here, I am constantly distributing bits of DNA into this room. And it’s these tiny molecules that represents the genetic breadcrumbs that tell us what organisms live in a specific location. In fact, DNA floats through the air, it is in the soil and in the water. Take a cup of water from a pond, and in five minutes you’ve likely filtered it out what species have passed through in the past hours or days.’

Easier than watching for days

That’s a lot easier than spending days watching whether a certain species of fish passes by, for example. That is why eDNA can be such an ideal research method particularly for rare or elusive individuals. ‘It’s a young field, I’ve been working in it since 2013. Then I went to Shanghai to do research on the conservation of the critically endangered finless porpoise from the Yangtze River.’

Kat Stewart with a crested newt, one of the species she is focusing on in her Vidi project. Photo: Manon de Visser

Goal: a handy toolbox

Stewart wants to develop a handy toolkit based on eDNA. ‘At the moment we mainly use it through barcodes: you see if a certain species is represented in the sample. I want to see if we can uncover patterns below the species-level and map populations across space. So that with a set of small samples from water, air or soil, we can get a lot of information about an area and learn to predict how invasive hybridisation occurs.’ Making it even cooler, if you freeze the samples, you can use them to answer all sorts of other questions later. ‘The samples are like time capsules.’

Focus: invasive species that breed with indigenous inhabitants

With her Vidi grant Stewart can now start a large project with several PhD students. She focuses on invasive hybridisation. In this process, an invasive species, usually introduced through human interference (think pet trade, ornamental in gardens, or hitchhikers in cargo transports), reproduces with a native species. ‘For example: in the Netherlands there are newt species under conservation protection. But there are now also invasive Italian newts that are spreading throughout the country. Sometimes these two newts breed together further damaging native newt populations – this is called invasive hybridization and it’s a potentially common and disastrous phenomena.’

Salmon, important for people and nature

Invasive hybridisation can have all kinds of consequences. ‘Salmonid species are incredibly important from a socio-economic standpoint as they represent the majority of fish from fish-farms. But they also are highly susceptible to hybridization which can also bring about disease, lower yields or mortality. In fact, rainbow trout (a Salmonid) is amongst the world’s worst invasive fish species, hybridizing with native species across the USA, Europe and Asia. And that has really big consequences!’

Consequences from the point of view of conservation biology – entire species can disappear as a result of hybridization; think global biodiversity declines – but also socio-economically. ‘Native salmon species are of economic importance, and for many indigenous groups for example, also of religious and spiritual significance. Losing these species can then have a negative cascade effect that may never be recoverable’, says Stewart.

With universities, government and a company

Stewart will be researching salmon in the US and crested newts in the Netherlands and across Europe. Both Salmon and newts have to deal with intensive hybridization pressure, both naturally and from human impacts. ‘It is a strength that I will be working with all kinds of stakeholders. For example, with RAVON, the knowledge organisation for reptiles, amphibians and fish. And with various universities, government institutions and a company.’

You have to know what motivates people

The Canadian biologist has extensive international work experience. She has worked in Canada, the US, Mexico, China and now in the Netherlands. ‘The Netherlands is very internationally oriented. Conservation biology has regional and global aspects. To get things done with different parties and to conserve species, you have to be pragmatic and know what motivates people in order to convince them. I think my international experience helps with that a bit.’

Text: Rianne Lindhout

Photo: Manon de Visser

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