Accidents happen: Sneaky invasive species

05 March 2019

Interview with

Sebastian Schornack, University of Cambridge

ASH-TREE

Two ash trees in a park

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Many scientific papers have drawn connections between invasive alien species and the extinction of native species, in particular vertebrates. Invasive alien species are listed as one of the drivers for biodiversity loss. But how do invasive species get into a new place? Katie Haylor spoke with Sebastian Schornack, who is a researcher at the Sainsbury Laboratory at the University of Cambridge where he’s researching the causes and the consequences of the introduction of tiny organisms.

Katie - Now, many scientific papers have drawn connections between invasive alien species and the extinction of native species, in particular vertebrates. Invasive alien species are listed as one of the drivers for biodiversity loss. But how do invasive species get into a new place in the first instance? Sebastian Schornack is a researcher at the Sainsbury Laboratory at the University of Cambridge where he's researching the causes and consequences of introducing tiny organisms which can cause disease. Hello, and welcome to the show, Sebastian!

Sebastian - Hello. Nice to be here.

Katie - So, first of all, how do invasive species actually invade? How do they get into a new place?

Sebastian - Well that depends pretty much on the species. The one that we are studying, which is a Phytophthora species, a fungus-like organism, actually lives in the soil and infects plants mostly in the roots; and so with plant material and infected soil you can drag around the species all over the world.

Katie - Ah, so is it humans moving it around that's the issue?

Sebastian - Yeah, mostly passively. They are not aware of it, but they drag it with them.

Katie - Okay. So it is things like, if you tread on some soil, it gets on your boots, you get on a plane and then we go on from there...

Sebastian - Yeah. Or when you when you have trade, for example, when you ship seedlings or young plants from country to country, with it comes some soil, and in that so there can be some pathogens.

Katie - Okay. What makes these new places more vulnerable, then, to these invasive species?

Sebastian - So wherever species evolve, they evolve together with their environment. So when they develop new aggressive strategies to infect more hosts, in turn, those local plants - those host plants they infect - they can also evolve to increase their immunity to basically fortify themselves. But when a species is located into a new environment, that environment hasn't had the chance to evolve new immune strategies. So it's being hit with an aggressive strain and then is basically being wiped out in no time.

Katie - Oh, I see! So the disease-causing organisms in their native place... other parts of nature around it have kind of adapted to cope with these diseases, which isn't the case in a new place.

Sebastian - That's correct.

Katie - Can you give us a few examples of invasive species? What are we talking about and where are we talking about?

Sebastian - So a historical one is Phytophthora infestans, the causal agent of potato late blight. It originates from Mexico, but with the potatoes it came into Europe and then finally also into Ireland. And with the potatoes that were grown on a massive scale it also could amplify, and when the weather was right and the agricultural practices were not correct, it actually produced this Irish Potato Famine that we all know about. And in today's life I would say one of the most famous ones in the UK is the ash dieback, which was introduced into the UK more recently, and it is killing ash trees. But all over the world there are several examples, and one of the ones that we're studying is Phytophthora palmivora pathogen, which scientists believe is from Asia but actually was introduced into several countries including, for example, Colombia where it infects oil palm plantations and kills oil palms.

Katie - Is this what is commonly known as bud-rot?

Sebastian - Yes that's correct. We don't know much about the pathogen, we need to know much more. But one of the open questions is, for example, how does a soil pathogen like Phytophthora, which sits in the soil and infects roots, finally is able to infect the top bud of a 30-year-old oil palm. And one hypothesis is that insects feeding on the infected roots actually bring the spores of the pathogen into the bud and then infect the palm. And the palm has a problem there, because it only has one growing point at the very tip - and when it's dead, that's it.

Katie - Okay so just to clarify this is a fungi-like organism that gets into, for instance, palm and causes a bit of mayhem. Are there other crops that are vulnerable?

Sebastian - Yes. So, when it comes into new environments it can use its powers to infect all these different, diverse host species. These species, they range from palms to cacao, for example, to mango, papaya, rubber trees, and so on. A lot of them are tropical species so there is no danger for the UK because the temperatures are not right and the humidity is not perfect but the tropics are pretty much in danger.

Katie - So, just how big a problem are we talking?

Sebastian - Well, in Colombia it has been reported that, let's say if you have a 2 billion revenue from oil palm plantations you lose about 200 to 300 million.

Katie - Can you talk us a little bit more about the UK specific examples?

Sebastian - The most famous one recently is the ash dieback fungus which is a fungus that is common to Europe, but there's different varieties of it, or 'strains' as we call it. If a strain that is not native to the UK is introduced, then it hits basically ash trees, which cannot deal with that strain. And the strain can very much infect them. And normally this is ash dieback fungi... they live in the leaf litter and they usually infect that material. But this strain somehow is able to infect living material - and that was one of the features that it had; why it was so aggressive.

Katie - Wow. So what can be done, then?

Sebastian - First of all, agricultural practices have to be improved. Knowledge about the pathogen has to be improved. The actual farmers have to be trained, so that they're aware what diseases are in their plantations. And then last, but not least, you can also take measures locally to prevent spread of these pathogens. For example, Phytophthora ramorum, which infects large trees in Wales; the advice there is that you're not dragging mud across different forests or that you clean your car or that you avoid roads that are muddy so that you make sure that you're not bringing spores from one area into a new area.

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