What animals did we find in the river?

We sampled the River Great Ouse for eDNA - what animals did it uncover?
10 August 2021

Interview with 

Kat Bruce, NatureMetrics


Water vole


Sally Le Page was very keen to find out what animals in the river Great Ouse were revealed by our DNA test with Kat Bruce from NatureMetrics...And Naked Scientist Phil Sansom, Eske Willerslev from the University of Cambridge, and Beth Clare from York University of Toronto weighed in...

Sally - We've got our sample, we popped it in the envelope. We mailed it to your lab. What happens in the lab?

Kat - It goes in the oven which heats it up to about 56 degrees for a few hours. And that just bursts open any cells that are still intact and releases the DNA into solution. Then we need to make millions of copies of the DNA of the particular group of animals or organisms that we're wanting to survey. And that gives us enough to be able to sequence.

Sally - So, you're only making the copies of the animals you care about?

Kat - Yes, exactly. Otherwise, if we just sequenced the DNA as it is in the sample, it would really just be dominated by bacteria and things. So, once we've done that, it goes onto the DNA sequencer. At the end you have a data file which has 30 million lines of As, Ts, Cs, and Gs. And of course that doesn't mean very much to most people. So, it then goes through a computational process, which sort of summaries that information. And then it runs each unique sequence against a reference library of known DNA sequences of species. And that lets us put the names onto the species that we've found.

Sally - And the big question is what did we find in the Great Ouse?

Kat - So, it takes a few weeks to analyse a sample from beginning to end for meta barcoding. So, in this case I've got some results from last summer when I actually came down here with a group of citizen scientists.

Sally - In true Blue Peter style here's some we made earlier!

Kat - Absolutely. And in total, so we did a vertebrate analysis on the samples and in total, we've got 23 species. Most of these are fish. So, 14 of the 23 species are fish, things like roach, perch... quite a bit of human in there as well. It was a busy day on the paddle boards! But then, you know, even things that are much lower level things like spined loach, this is quite an important species in this area, actually it's really hard to survey because it just sits around at the bottom of the river and is not sampled with electrofishing.

Sally - That's incredible. And looking down the list, we got a whole bunch of fish. You've got your dace, roach, chub, but we've also got super exciting things like water voles. They are incredibly rare now in the UK and very hard to spot.

Kat - Yeah, absolutely. They are a protected species. A lot of effort goes into trying to survey and confirm the presence of water vole.

Sally - Just looking around, we're not even in a particularly quiet part of the river, there's boats going past, we've had lots of dog walkers. I can see the reeds, but I never guess that we've got water voles that we've got all of these fish species. We can't see down to the bottom of the river and they're just there and you can tell with their DNA.

Kat - Yeah. And what we really want is people to go, oh my gosh, now we know that these species are here, we're going to come in and look for them and get interested in them and then come to these places with more of a sense of what the place is and what you're sharing, what other species you're sharing the places with.

Phil - Sally, I've never even seen a water vole.

Sally - I've only seen one. And I was incredibly excited when I first saw them. They are, of course, Ratty from Wind in the Willows and their population has dropped. They're so hard to see and they were in the water.

Phil - Is that in line with your predictions, you think?

Eske - I think it's pretty well what you would expect from this.

Beth - Nobody is ever going to look at water or air or soil again once we start talking about what's in it, because these things are just soups. It's just everything that's been through leaves behind a trace of itself. And what eDNA is doing is letting us look at those traces, unlocking that little mysterious door. And as you said, see what's invisible.


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