Sep 05 2019

DNA Analysis of Loch Ness

If you have never been to the highlands of Scotland, add it to your list of places you should visit. It is incredibly beautiful. When I was there last year we visited Loch Lomond of lyrical fame, and also the largest lake in Great Britain. We were given the option of instead visiting Loch Ness, and we had to explain to our guide that she had a bus full of skeptics. She was relieved because she thought Lomond was the better destination, but of course most tourists want to see the more famous Loch.

The legend of the Loch Ness Monster has now taken on a life of its own, and it seems unlikely that any evidence, no matter how definitive, will kill it. Rumors of a monster in the Loch go back centuries, but the modern myth was kicked off by the famous Surgeon’s Photo. In 1934 Colonel Robert Wilson, a British surgeon, published his now iconic photo. His accomplice later confessed this was a hoax, using a model built out of a toy submarine and a clay head (which I always thought looked like it was modeled after an arm and hand). But it was too late, a myth was born.

A recent headline from the BBC now declares: “Loch Ness Monster may be a giant eel, say scientists.” The problem with this claim is that there is no Loch Ness Monster, so it can’t be anything. Of course they mean that giant eels may be responsible for Nessie sightings, but even this is misleading. There is likely no single phenomenon responsible for the continued sightings of something unusual in Loch Ness.

Many tourists go to Loch Ness to catch a glimpse of Nessie. There are lots of things that can be mistaken for a lake monster – including living things swimming on the surface, but also floating logs or other debris. At best they found one possible cause, among many, of curious sightings in the Loch.

The BBC, however, fell for the framing provided by the researchers, likely fully aware they were doing so because both they and the researchers benefit from this – more clicks and attention. What is really going on here is that scientists are conducting a DNA analysis of the Loch to evaluate its ecosystem and see what is living there. Would you be more likely to read a news reports about a DNA survey of a British lake conducted to determine what types of fish and other creatures live there, or one about an explanation for the Loch Ness Monster?

The scientists even acknowledge they were not specifically looking for Nessie, just surveying the lake. But they got the headline attention they were looking for.

In any case – this kind of research is pretty cool. You can take a container of water from a lake and then analyze the DNA that is floating in the water, to determine which species are living there and get a general idea about their abundance. Animals shed DNA all the time, especially those swimming around in a body of water. So the lake is a soup of DNA of all the things living in it. You don’t have to actually look for or sample the specific creatures – you can just scoop up their DNA.

The researchers sampled different parts of Loch Ness and found that eels are very common. So they speculate that giant eels might be confused for the famous monster. However, they have no evidence that any of the eels in the Loch are “giant” or that any photo presented as Nessie is actually an eel. There are just lots of eels in the Loch, which is apparently already well known to the locals.

More significant for Nessie enthusiasts is what the scientists did not find. They did not find any DNA from a large reptile, putting to bed the unnecessary speculation that Nessie might be a plesiosaur left over from age of the dinosaurs. They also found no DNA from sharks or sturgeons, which are more plausible hypotheses offered to explain some of the sightings.

The science here is pretty cool, even without the Nessie angle. Normally it is very difficult to prove a negative – that none of a certain type of creature exists. Large lakes, and in particular the Scottish Lochs, can be very deep, and can therefore hide many secrets in their murky depths. It’s normal for the human imagination to wonder what lives beneath the surface. Traditionally we can answer this question by simply looking – sampling the life in the lake. By doing this we can easily find the more common denizens of the lake, but how much do you have to look before you can confidently conclude that some species is not present in the lake? This logic has given comfort to Nessie believers for decades. The creature can always just be hiding in the depths, missed by any survey, no matter how thorough.

But you cannot hide from this kind of DNA survey. Any creature, especially a large creature, will shed lots of DNA and this DNA will spread to at least some extent throughout the environment. This is called environmental DNA or eDNA. Sample the water in enough locations, even at depth, and you can be reasonably sure that if you find no DNA from a particular species, it does not exist in that location. Of course there are false negatives, no technique is 100%. But this is much closer than we have been able to get before. This technique can be applied to any body of water in the world, giving biologists a powerful tool to survey various ecosystems.

The story of eDNA is a great one. I hope it does not get lost in this article focusing on Nessie and eels.

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