Who Eats Whom in The Undergrowth
Chris - Now you're trying to solve the puzzle of who's eating who. Tell us about that.
Michael - Yes, it's true. I'm interested in what's going on below ground and who is eating whom. There are many animals, about four to five hundred different species, and the complicated thing is that these animals contain no hard remains of the prey for you to identify.
Chris - So it's all been digested.
Michael - Yes, digested, liquid things. However, you can use DNA-based methods that track the gut content of these animals, look at the DNA that they contain and then you know what they've been eating.
Chris - So which sorts of animals have you been playing around with?
Michael - We've been looking at different sorts of animals: beetles, millipedes, centipedes, earthworms and nematodes.
Chris - So was that not known then?
Michael - It's very hard to study and observe because it's below ground. It's also hard to look in undisturbed conditions. That's normally the problem. You can't put, for example, a plastic or glass sheet into the soil and watch the animals, because you only see the animals that come up to the glass sheet.
Chris - And you wonder whether you have changed the situation by doing that.
Michael - yes, you change things completely. It's hard to get really quantitative data, and really understand and see what's going on. So with DNA based methods it's really a new thing and a fascinating thing that we can analyse samples. In Austria, we have collected 500 predators from the soil because we were interested in who is eating the white grubs. They are pests in soil ecosystems. We found out that some centipedes called geophilites are probably the most important predators of these soil pests and this wasn't known before because there was no technique available to study this.
Chris - Talk us through the actual nuts and bolts of it. How do you do the experiment? What does it actually involve?
Michael - First you have to sequence
Chris - Well hang on, you have to collect the animals first, so where do go and do these experiments?
Michael - Ok, you have to go to the field, dig into the soil and collect animals. You then freeze them immediately because it's important to freeze them as quickly as possible.
Chris - So the gut contents don't go off.
Michael - Yes, so they don't go off. Then you bring them to the lab and you extract them using methods that are a bit more sophisticated than your kiwi experiment.
Chris - So what does that involve?
Michael - We crush them and extract the DNA. But we still have the problem that they contain lots of substances that inhibit your PCR reaction. That reaction is later needed to identify the specific DNA molecules. So we crush them and get the DNA from the predators, including their gut contents, and then we throw all this together in a nice optimised PCR reaction.
Chris - Polymerase Chain Reaction.
Michael - Yes, and add some particular genetic markers that target, for example, white grubs or cockchafer, and then if the predator was feeding on this white grub, you get a positive result. You will see a band on an agarose gel. Then you have proven that these predators or this centipede was feeding on the cockchafer.
Chris - Sounds good, but my worry here is that what if the grub crawled through the soil that another one of these animals has already died in and got some of that DNA on its body? DNA techniques nowadays are so sensitive that couldn't you get some contamination? Couldn't you be fooled into thinking that something had eaten something even if in reality, it hadn't?
Michael - Yes. There are always problems but I don't think that this would be that problematic if it was just crawling through the soil and contained some of the DNA of the target prey. There are lots of microbes in the soil breaking down the DNA. One problem that we are really struggling with is differentiating between active predation and feeding on dead prey, or scavenging. This makes a big difference.
Chris - Can you solve that problem?
Michael - Not really at them moment because you can't pick up the DNA from dead prey as good as you can from fresh prey. Forensic scientists are using this powerful PCR to get DNA from human bodies.
Chris - It's amazing to think that we've got to the stage where there wasn't the knowledge of what was going on underground. There must be some other spin offs from this for maybe agriculture and commerce.
Michael - The basic idea and the reason why we did this project on the white grubs was that white grubs are very serious pests in alpine grasslands ecosystems. We were interested in what below ground predators there are for the grubs and see which predators we should enhance. What are the ky plyers in regulation?