Instant Genius - How climate change is disrupting nature’s ancient symbiotic relationships

Episode Date: May 11, 2025

Be it a pair of wolves that mate for life, a pod of female dolphins that hunt together, or a large colony of honeybees all working together in a hive, the natural world is filled with relationships of all kinds. But some relationships run deeper than others, even to the extent that certain species literally make their homes inside the bodies of others. This is an example of a symbiotic relationship – a long-term bond that exists between organisms of different species. In this episode, we speak to science writer Sophie Pavelle about her new book To Have or to Hold: Nature’s Hidden Relationships. She tells us how far from being rare, symbiotic relationships occur practically everywhere in the natural world, how they come in a dizzying array of different forms, and how the fine balance underpinning these relationships that has formed over thousands of years is coming under threat from human activity and climate change. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Science Focus. Be it a pair of wolves that mate for life, a pod of female dolphins that hunt together or a colony of honeybees all working together in a hive. The natural world is filled with relationships of all kinds. But some run deeper than others, even to the extent that certain species literally make their homes inside the bodies of others. This is an example of a symbiotic relationship, a long-term bond that exists between organisms of different species. In this episode, we speak to science writer Sophie Pavel about her new book, to have or to hold, nature's hidden relationships. She tells us how far from being rare, symbiotic relationships occur practically everywhere in the natural world, how they come in a dizzying array of different forms,

and how the fine balance underpinning these relationships that's formed over thousands of years is coming under threat from human activity and climate change. So welcome to the podcast. Thanks very much for joining us. Thank you for having me. It's great to be here. So today we're talking about your book, to have or to hold. nature's hidden relationships. So it's all about symbiotic relationships. So let's start with the obvious question. What exactly do we mean by that? So symbiosis is a word to describe the situation of organisms that are different species living together. So it comes from, or it loosely

stems from the Greek word meaning living together. But actually it has lots of different iterations, but essentially it's like an assemblage of totally unlike organisms, finding survival in an essence of living together. So is there any difference between a symbiotic relationship and a parasitic one? Good question. And it's something that I don't think science still really knows the answer to. Symbiosis can have many different interpretations. But what I found, which was unexpected, is that I always wanted to explore,

symbiosis in writing to have or to hold, but I wasn't expecting to be exploring symbiosis from a parasitic sense quite so much. But parasitic relationships are where species rely on the body and or brains of another species for survival to complete part of or all of their life cycle. And so that, by its very nature, induces some sort of suffering of the host species and there can be one host, there can be multiple hosts, depending what species of parasite we're talking about. And if we're looking at symbiosis from the sense of species living together and they're unlike species, then parasitism is very much a dominant form of symbiosis. And the more I got into studying and researching and speaking to experts, the more I realized

that actually any form of symbiosis is in some way a form of parasitism because there is no, from what research is discovering and research is completely unfolding real time on this subject as we speak, there is no situation where both species benefit. There is always one species who benefits slightly more than the other, which to me is really intriguing and part of its mystery. Yeah, that is super interesting. And I think a lot of people might think, oh, well, that's sort of a niche area of biology in a niche way that animals or organisms live.

But it's a lot more common than you'd think, really, isn't it? Yeah, totally. So there was a paper by the Royal Society a few years ago that estimated that over 50% of biodiversity is made up of species living in parasitic relationships or in, and actually that has broadened out now into nearly every part of natural history and biology is caught in some way or is in some moment involved in a parasitic relationship. I mean, we as humans have over 400 species that rely on our bodies to complete their life cycle in a parasitic sense. So it is pretty much everywhere. And in that sense, it's kind of quite a nebulous topic because the more you look,

the more you see. And it kind of is never ending. Yeah, talking about humans, you just reminded me or something. It's a bit of icky, but those like mites that live on your face. Yeah, yeah, everywhere. And just it's a classic thing, whether it's the same kind of logic as looking at marine environments and freshwater environments and things are hidden underwater or in the night sky, just because we can't see something doesn't mean it's not there. And that, again, is really

intriguing to me because it just opens up this whole universe of multicellular, complicated life that is so essential to ecosystem stability and resilience against climate change. Yeah, so we'll get into that sort of a bit deeper later on. But in the book, you split the chapters up into specific symbolic relationships. So what I was interested in is, how did you choose which ones to pick? Oh, it was so difficult. So there were several pieces of criteria that sort of helped me structure the choices. So I wanted species that existed in relationships that were accessible around the British Isles.

So I live in Devon, in the British Isles, and I wanted these relationships to be somewhat tangible to readers in the UK. So this book that will be published in the US and there are lots of elements of research that are globally significant in the book. But I wanted to be able to travel and go and see them or try and experience their environment for myself, which helps in a writing sense because it sort of helps immerse you into their world, even if briefly. So they had to be in the British Isles. And I wanted to get into different environments. So I wanted species that would allow me to talk about the open ocean and marine ecosystems from a sort of pelagic sense, so open ocean right the way through to the rocky shore into tidal sections, rock pools, beaches,

that sort of thing. And I was desperate to get into the forest. And so we've got two chapters that talk about woodlands. So we've got ancient Aspen woodlands up in the highlands of Scotland and then temperate rainforest down in southern Ireland. So that was a really exciting opportunity to be able to talk about symbiosis from the connection. between trees and fungi and soils and that sort of thing. But yeah, it was kind of, I had an idea of some specific species, but I was open to flexibility in that once I started to meet certain scientists who were researching some of these species,

often they would give me recommendations of specific interactions to focus on that might give me an opportunity to really get into the more gruesome side of symbiosis that people are so averse to, but it's so essential for us to be aware of. So that's where the hairworm came up, for example. And then animal algae, which is the plant, animal worm that is chapter one, that just captivated me immediately was actually meant to be a species of slavemaker ant, but it was only when I met the scientist that he actually said, oh, well, we're researching this worm at the moment.

And I think that would be a fantastic example of symbiosis for readers to wrap their head around. So it sort of was a state of flux all the way through, which I guess is a very nature of symbiosis in a sense. Yeah, so you're saying that you're actually putting a lot of legwork on this, like covered a lot of miles. Literally. Did that present any particular challenges? Oh, completely. So I like to try and do my book research via low-carbon travel as much as possible.

I love adventure and sport and cycling in particular. And so that was kind of a non-negotiable part for me to sort of, how can I get around to these places from England, Scotland, Ireland, Wales, Channel Islands. via low-carbon means on a low budget, which was just naturally my restriction anyway. So ferries, trains, cycling, walking, running, that sort of thing. And it just so happened that I travelled mainly during 2020, 23, 2024. Nearly every single book trip was accompanied by a named Storm. And I would like to have words of the mess office about this. Because it made the travel complicated and quite volatile.

but actually on reflection, traveling during storms and in the wake of storms and being disrupted by storms was a point of conversation in itself because that was a huge talking point. Okay, well, why are we having such volatile weather? Why are we having quite so many storms? And I realized when I was again reflecting back on these trips, I was traveling during unprecedented marine heat waves, during unprecedented terrestrial heat waves. And all of that was, I was living through the British Isles going through a, a tumultuous weather system on the back of an El Nino. So that was, I think, a valuable experience to be able to reflect on these species that I was trying to find because the caveat of this whole book is, okay, well, these relationships

are ancient, they're complicated, they're sophisticated. What is climate change doing? Is it coming in as a disruptor, potentially breaking them up? Is it bringing in new participants into the relationship? And what does that mean for these ecosystems and their resilience against further change? So let's have a look at one of the examples then, which is the shore crab and the barnacle. I've picked this one out because it's particularly, I think it's the sort of what people might think of when they think of a symbiotic relationship. So first off, like, we're probably all heard of barnacles if you've watched Tintin or Red Tintan.

But what exactly are they? Well, they look nothing like a barnacle that you would be familiar with. So I grew up on the coast in Devon and I associated barnacles with grey's knees and bruised legs from scrambling and scrambling over rock pools and just time on the beach. But these barnacles, so this particular species I focus on is called Sacculina. So that's its Latin name. But fortunately it's friendly enough to say that it can sort of roll off the tongue. It's not one of these really complicated Latin names that you never want to read again. So Sacculina looks like, I don't know, some kind of.

kind of alien. If you were to Google it or search for it online, the larval stages look more like a kind of alien invertebrate sort of thing with froms and antennae and things, as opposed to the sort of shells barnacle that you're familiar with. So that's immediately cool to me, and I liked that. But it's structured and has evolved in a way to basically be an invader. And the species it wants to invade our shore crabs. Now we all know what shore crabs are. They are one of the most common crabs on our shoreline and they are sort of associated with quintessential seaside times. But luckily for the shore crab, it is one of the favourite hosts for this species of barnacle. And this barnacle would like to invade the body of a shore crab, male or female, in its larval stages, and basically

grow and spread almost like a fungus inside the body of a crab. And then, that's the body of a crab. then the way it emerges is it mimics the egg sack of a shore crab and basically fools the crab, the poor crab, the crab host, into caring for the barnacle as a fake egg sack because the crab, this is sort of anecdotally speaking, I'm pretending to be a crab, I would look down and I would see an eggbird and think, oh, wow, I'm pregnant, how did that happen? But, oh well, I'm just going to care for it and nurture it as I would my own offspring. all the while they are caring for the parasite, nurturing it, feeding it, allowing it to grow, and then at some point the barnacle would be ready to drop off and spread its own offspring.

And the poor crab is left in a bit of a sorry state. But what's fascinating is that if the crab host is male, it's likely that the barnacle would undergo a procedure that's known as parasitic castration, where it would actually remove or sever the testes of this male shawl crab in a process called feminization, where it would feminize the crab, falling it into pregnancy, a false pregnancy, and undergo this sort of nurturing of the parasite that I just described. But what's fascinating is that this feminization isn't necessarily a permanent thing. There have been studies showing that crabs can regrow their testes and return to being male. I can't imagine they'd

feel great after that ordeal, but it's just one example of this incredible interplay between completely different species that's going on right under our nose. So you called it an invasion. So how does that invasion take place? You know, what happens? Well, studies have shown that the larval stage of the sacculina barnacle is very sensory in that it seeks out a crab host that is unoccupied by a sacculina by smell. So there's something about the crab that the larval stages of sacriena really like, the smell of it.

and it helps them sort of navigate. Let's imagine it's a really busy intertidal, volatile environment. There's a lot going on in a given intertidal environment. And so the sacculina have evolved to be very purposeful and guided by scent. And they latch onto the crab in some way and sort of invade from the inside or from the outside and go inside. And then, again, studies have shown the way they ramify throughout the body of a crab is almost like a fungus.

They have these rootlets that grow. and grow in these sort of spectacular tendrils and they sap on the resources that the crab provides. Without the crab really knowing, the crab can still function, the crab still moves around, and it's necessary it does that because a parasite never wants to kill its host necessarily because that's a waste of time, it's a waste of energy, a waste of resources. It needs to be as covert as possible so that the host can provide as much resources as the parasite needs. So yes, it spreads like a woodland, and I think I describe it like that in the book. And it's this lovely sort of mirror image that nature repeats patterns in these ways, which clearly are successful.

So you think, like, how can the crab sort of defend itself? Because you talk about molting, you'd think, you know, crabs molt their shells. I think maybe it would be able to get rid of it by doing that. Yeah, it's a really good point. And so the molting cycle of a crab is vital. So a brilliant academic who's based out of Aberystwyth University called Dr. David Wilcoxon studies circadian rhythms in crabs. And it's basically the internal clock that governs the molting cycle, which is one of the most important cycles in the natural world to allow crabs to grow and move around and breed as a sort of apex predator of the intertidal zone. And what they're finding is that sacculina as a parasite can actually inhibit. this essential malting cycle and circadian rhythm.

And that is a classic parasitic strategy to sort of invade the biological clock because that sort of protects the internal organs in a way that they can still get those resources they need to grow and complete or continue their life cycle. But there are studies showing that crabs in their sort of immune system can retaliate to a sense because there's this process called melanization where there's this darker tissue in dissection where crabs have been infected by sacculina. And melanisation occurs where there's been an immune response to an invader or some kind of thing that shouldn't be there.

But again, what they're finding is that sacculein almost knows that and can be so covert that they can sort of silence or evade the immune response such that it doesn't reject them. They can still sort of do the work that they need to do inside the crab and become that false egg sac. false egg burden and reproduce themselves. So again, it's so sophisticated. And obviously it's taken millions of years

for those systems and that relationship to evolve and to be so almost in time with one another such that both species technically could still survive and breed themselves. But as I said at the beginning, it's never a mutual thing. There's this tussle, this give and take, such that the crab generally is going to be worse off

in that relationship than the barnacle. So having said that, is there anything at all in it for the crab? That's the big question throughout the whole book, all of these relationships, is what's in it for them? And does the host actually ever get anything out of hosting a parasite? And it's a really difficult question to answer because you can stray into kind of a subjective human perspective on that. So I don't think I have a really good answer if you there

because I think scientists are still uncovering that in terms of in these entwined entanglements, what actually is each participant getting out of it? Because it's very easy to go on the parasite side and say, well, they're getting loads out of it, but actually they sacrifice a lot to be in that position as well. So, yeah, it's a tricky one. And I think it's the sort of governing question

that overrides any understanding of these complex relationships. You said this place was steps from the water. We just haven't found the steps yet. How much did we save? Enough. Enough to get lost. Or you could book a stay with Hilton. Welcome to your oceanfront room. Just steps from the water. The Hilton sale is on now.

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The buffish mining bee. What a great name. And the early spider orchid. So the bee is what's known as a solitary bee. I always feel sorry for solitary bees. It's kind of a sad name, isn't it? They don't get to live in the hive with all their pals. They just buy themselves.

So what do we know about this little guy? So the buffish mining bee is a very important solitary bees. So solitary bees as a group of bees are incredible pollinators. They're like the Paragon pollinator. But they kind of get overshadowed by the PR of a honeybee and the kind of cute fluffiness of a bumble bee. But solitary bees can have phenomenal pollination power and we really, really need them. But unfortunately, as with many insects in the British Isles and beyond, they're having a difficult time at the moment. But the beauty of the relationship between the early spider orchid and the buffish mining bee is that the early spider orchid pretends to be the female buffish mining bee.

and fools the male buffish mining bee into mating with it. And while it's pretending or attempting to mate, it's fooled by a almost near identical cocktail of pheromones, which is incredible, almost exactly the same as a female bee. The orchid looks, feels, smells like a female buffish mining bee to a hungry male bee. And while the male is being fooled into mating and is literally in contact with the flower trying to mate thinking it's a female bee, the orchid is being pollinated. And so that happens if everything's going well. With rising spring

temperatures, everything moving forward, everything getting out of whack, the female bee is beating the orchid by emerging first before the orchid is flowering. And so if the female bee is around, the male bee is also around, the male is naturally going to be going towards the actual real female bee mating with them instead of the orchid. And so because of that, the orchid, are not being pollinated. And this is a flower that is a quintessential species of chalk grasslands and meadows across the country. And if they can't be pollinated, they can't, you know, grow in populations. So this is an orchid that is running out of time.

And this bee is everything to the orchid. But what studies are finding is that the bee can quite easily rely on another flower and isn't dependent on the orchid as much. So it's a tough question, but I think a lot of people will be thinking, well, this relationship between, in this case, the bee and the orchid, is so delicately balanced. You know, can we even say how that arose? Just time, I think, you know, orchids are one of the oldest flowering plants, evolutionarily speaking. And then pollinators are obviously very ancient insects that emerge about 60 million years ago, I think, after the dinosaurs became extinct.

And so over millions and millions of years, they have sort of found a beat with one another. But I can't say how apart from time, these things evolve such sophisticated. I mean, for a flower to mimic almost exactly the pheromones of a specific female species of bee is insane. And it just highlights to me how little we really know about, as you say, the delicacy of the natural world

and what that actually means for the wider ecosystem and the other species within it. By way of closing, let's sort of explore that then. So like we say, everything's in such a fine balance, but things are changing more rapidly than ever, you know. How dire is the situation? And is there anything we can do, you know, to help these species, you know, what's the current science?

Well, I mean, it's a lot. So if we're following on from talking about flowers and bees and pollinators and how they interact, light pollution is a huge issue for pollinators. So 80% of people at the moment around the world exist under light polluted skies. So anthropogenic light, so light that we've generated and are generating. And that's that anthropogenic light, which isn't useful, spills almost as waste into forests, into oceans, into rivers. and there's been research that's quite devastating really because it shows that artificial light at night keeps pollinators, some pollinators active

to the point where it actually exhaust them and some people have likened it to, if you've been at the gym and you're working out and you just don't stop and you get exhausted and you burn out. Studies are finding that pollinators are literally burning out under lit skies at night. And alongside that, so the world is too bright, it's also too loud. So around 60% of Europeans are living, working, playing against the soundscape equivalent

to falling rain as a constant droning in the background. That's not normal. And every extra decibel can actually half the distance over which natural sounds can travel. So I'm talking about things like barking dogs, traffic, construction, agriculture. studies are finding that this is literally ripping food chains apart because species are spending more time running away from sound and a state of fight or flight than actually doing what they were born to do, which is interacting with their environment and other species. So we're talking about a parasite might struggle to find their host in noisy, artificially

lit places. A parasitic stage could become lost from a point in their life cycle, meaning the life cycle can't close, it can't complete. And so we're risking just by living our lives in the way we are being advised to, i.e. busily, productively, at all hours of the day, we are potentially tearing food chains apart and separating species from one another when we're now understanding through symbiosis and parasitism that that will just cause a ripple effect of a domino. you affect one species, you affect many.

And that's not new science at all. But I think just having a better understanding and an awareness of this specific interactions and what that actually means and how that can stabilize ecosystems, that suddenly holds new significance for me. And while I was writing, the UN changed their sort of designation of global warming that the planet is no longer nearly warming. It's actually boiling.

And on the flip side, we're living in the UN's stage, decade of ecosystem restoration until 2030. The UK still ranks bottom in Europe for measures of nature connectedness and we've lost more wildlife than any other G7 nation. So we're at a point where we've interfered so much that we've almost got to interfere again to try and slow this destruction that we're speeding up. So in terms of what we can do, it's both a worrying time but also I think a very exciting time especially to be in the sector of science communication because what all of this is telling me is that we need more stories we need more people talking we need to almost revolutionise how we view our natural

world because I think we need to see it as something that we cannot live without that we are inextricably tied to and so to how to how to to hold as a book about relationships. And so I'm trying to, through the book, advocate for a relationship to nature that's underpinned by the qualities that we all seek in our own relationships. So taking responsibility for our actions, establishing boundaries, having curiosity, having respect, showing gratitude, showing up in nature on a walk, wherever you are with intention and almost looking at a relationship with nature is something that's built on trust and servitude and, you know, like you would have with a friend or a family member,

you kind of, as a human, you have innate concern for their safety and health. And I think there's no reason why we shouldn't do the same for nature. So nature, through all of the relationships I profiled, has inordinate quantities of lessons that help us or that sort of give us an opportunity to have a good long, hard look at ourselves in the mirror as to how do we want to conduct our relationship with nature? Because at the moment we're at risk of being the parasite to our host. But it doesn't have to be that way. And the science is really exciting as to how studying symbiosis

and these interactions can actually help us navigate, live and work better together. So there's a lot of hope, I think. And I think just being at a point where there's so much we don't know and viewing that as exciting and motivating, I like to think, is a good perspective to have. Thank you for listening to this episode of Instant Genius brought to you from the team behind BBC Science Focus. That was science writer Sophie Pavel. To discover more about the topics we've just discussed, check out her book, To Have or to Hold, Nature's Hidden Relationships. If you liked what you just heard, then please do consider some. subscribing to Instant Genius on your preferred podcast platform.

If you'd like to see our hosts and guests in person, then please do also check out our YouTube channel at ScienceFocus. The current issue of BBC ScienceFocus magazine is out now. Pick up a copy wherever you buy your favourite magazines or download us on your app store of choice. You can also find us on Apple News or online at sciencefocus.com. This podcast is sponsored by name, audio and focal. The texture and emotional depth of music

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