Crack an egg in a pan, turn up the heat and you can witness a kind of magic. In just seconds the viscous egg solidifies. And despite the rising heat, it’s the opposite of melting that occurs. I was a teenager when I heard a biology teacher explain this paradox: “The egg is full of proteins and the heat has denatured them”. Denatured. The word was new to me. Twenty-five years later I find it is a fitting descriptor of more than just wayward proteins.
My teacher had explained that every protein has a temperature at which it will function best. Too hot or too cold and the protein’s shape can buckle or break. It will no longer be able to bond with other chemicals. It will cease to work. I think about that fried egg often when I consider what rising temperatures could mean for the planet.
We know that when people die of heat stroke, part of the problem is that some of their proteins have denatured. Could our cells become our jailors?
The proteins inside us and every other living thing vary greatly. Some tolerate heat better than others. Others begin to destabilise at just a couple of degrees warmer than normal. It is not the average protein that poses a problem, but the weaker links, those most liable to destabilise in extreme heat. We don’t know yet which of them are also critically important – to our food crops for instance.
As the world warms, what will happen to the millions of different proteins in the millions of different species, from spores to sperm whales, soil bacteria to sunflowers? These invisible structures are central to life itself. They give shape not only to hair and to horn but also to hormones and enzymes and DNA. They are the messengers and mechanics that control and correct processes in and between cells. Like the gaps in music that make the beats thrilling, these in-between places are where wonder is born.
It’s the same between species. Life is not a zoo of caged individuals living in isolation but a web of shared destiny. And while activists go on about polar bears or other creatures in danger, I am more curious about what climate change could mean for the way species interact and provide us gifts as a result. It’s been on my mind since the early years of my career when I lived in a rainforest in Borneo and studied the most fascinating of plants, the strangler figs.
Every one of the 750 or more species of fig trees depends for survival on its own species of tiny wasps to pollinate its flowers. The wasps in turn depend on the figs, the only places in which they can lay their eggs. This mutual reliance combines with the wasps’ short lifespans to ensure figs are available year-round, and because of this they sustain more species of birds and mammals than other plants. In return for the fig flesh those creatures disperse the trees’ seeds, and provide the same service to thousands of other rainforest plants. These interactions between fig trees and animals help to sustain the great rainforests of the world.
What does this have to do with climate change? Researchers have shown that just a small increase above current temperature levels will shorten a fig wasp’s life to just a couple of hours – not enough time to find a fig, pollinate its flowers and lay eggs. No pollination would mean no ripe figs for animals to eat, and this would mean fewer seeds get spread from place to place. Tree species that form a key part of the forest and its capability as an ensemble to lock away carbon are likely to suffer.
The tiny wasps are frail but some of the fig trees’ bigger partners are at risk too. They include fruit bats called flying foxes that can carry seeds 50 kilometres or more before pooping them out, making them some of the most effective seed dispersers around. Their vulnerability became clear early in 2014 when thousands of them fell dead from the sky during a blistering heat wave in Queensland, Australia. For both the bats and the fig wasps, the heat was too much. It will have interfered, at a cellular level, with proteins that cooked and then closed for business. These snapshots suggest trouble in store for the fig trees and the forests, whose fates entwine with our own.
Ecology teaches us that no species is an island. It’s a lesson our leaders seem to have skipped. It shows us we’re all in this together, the fig wasp and the fruit bat, the you and the me. That’s what makes the human fingerprints all over climate change all the more ironic. As we develop societies ever more distant from nature to protect ourselves from its wild whims, we risk unleashing upon these denatured societies powers we cannot hope to control or even predict.
This post reproduces my contribution to Culture and Climate Change: Narratives, which launched on 24 June at the Free Word Centre. The whole book is available for free and anyone can reproduces its articles under a Creative Commons Licence.
From the wings of tiny creatures hang the fates of hundreds of bird and mammal species, and perhaps even entire rainforests. They are fig wasps and they play a disproportionate role in the grand drama of life on Earth. They shape our own story too because of this. But new research warns that these insects could be “extremely vulnerable” to global warming.
This matters because each of the 750+ species of fig tree (Ficus species) relies utterly on particular species of fig wasp to pollinate its flowers. Without the fig wasps there would be no fig seeds to create the next generation of trees, and there would be no ripe figs for animals to eat.
In the case of any other group of trees this would not be such a big deal, but figs are special. Their pollinator wasps only live for about a day and each wasp species can only lay its eggs inside the flowers of its specific fig partner. So, to keep their pollinator species alive, each fig species needs to produce flowers and figs year-round. This means a year-round supply of food for birds and mammals, and helps to explain why figs feed more creatures than any other trees do (see A job for conservation’s keystone cops).
In the late 1990s, I set out to find out just how many animal species eat figs. The answer is an astounding 1,200-plus species, including ten per cent of all birds and six per cent of all mammals – see Who eats figs? Everybody). That’s the variety of life that stands to suffer in some way if fig-wasps disappear. Now, in a new study in the journal Biology Letters, Nanthinee Jevanandam of the National University of Singapore and colleagues provide a chilling insight into what a warmer world could mean for these wasps.
In a laboratory, they exposed the pollinators of four Ficus species to temperatures between 25°C and 38°C and to a various levels of humidity. The lifespan of all four species fell steadily as the temperature rose. By 36°C, the lifespan of three of the species had fallen to just two hours. In the wild this would give the wasps hardly any time to find a fig of the right species in which to pollinate and lay its eggs. It would hurt both wasp and fig species. This is the Achilles heel of a partnership that has existed for 80 million years. It is here that we might expect to see the relationship break down, with consequences for other species.
This has happened before. In the 1990s, fig-wasps in northern Borneo went locally extinct after a severe drought, and in Florida they disappeared when a hurricane wiped them out. In both cases, fig-wasp populations eventually bounced back — thanks to the fact they can disperse for tens of kilometres in the day or two they live. But a sustained temperature increase — like that which climate scientists predict will be a reality worldwide by the end of the century — is a different matter. As we turn up the global temperature we change the chemistry of life.
I asked Nanthinee whether she thought fig-wasps could adapt to a rise in temperature, either in their physiology or their behaviour — by flying at a cooler time of day for instance. “Fig wasps can produce up to 12 generations in a year in the aseasonal tropics, and so acclimation or genetic adaption is a possibility,” she said. “But more research has to be carried out to ascertain this. As to the possibility flying at different times, it is difficult to predict.”
The wasp species she and her colleagues studied came from distinct branches of the fig-wasp family tree, so they think their results will be relevant to hundreds of other fig-wasp species, the trees they pollinate and the animals that eat their figs. But these little wasps might have surprises in store for us yet. After all, they survived the mass extinction that saw off the dinosaurs, 65 million years ago. They might outlive us too.
Their story is a reminder that we are just new here, and that between our kisses, our fights and our smiles, we tend to stumble about breaking things before we know how they work.
Valisia malayana fig-wasps at a fig of their host tree Ficus grossularioides (Nanthinee Jevanandam)
Jevanandam, N., Goh, A.G.R. & Corlett, R. 2013. Climate warming and the potential extinction of fig wasps, the obligate pollinators of figs. Biology Letters 9: X-X. Published online March 20, 2013 doi: 10.1098/rsbl.2013.0041
“The proper way to eat a fig, in society,” wrote DH Lawrence, “is to split it in four, holding it by the stump, and open it, so that it is a glittering, rosy, moist, honied, heavy-petalled four-petalled flower. … But the vulgar way, is just to put your mouth to the crack, and take out the flesh in one bite.”
I’m a vulgar fig-eater. Few things give me more pleasure than when I bite into a ripe one and eat it up. With the right fig, the flavours can be so intense, so rich that it seems clear to me that no other fruit can compare. But the figs I eat are of just one of nearly a thousand fig species, and what eats the others is really interesting.
Take the keystone away from an arch and down will tumble the whole structure. Take a keystone species away and — so the concept goes — other species will go extinct too. In his excellent recent feature for Nature, Ed Yong explains how biologist Bob Paine came up with the concept while he studied starfish in the 1960s.
Paine’s keystone species concept “would go on to be applied to species from sea otters to wolves, grey whales and spotted bass” and — a group Ed missed from the list — wild fig trees, whose huge crops are available year-round and keep more animals alive than any other species.
For this reason, Ed’s article brought a blush to my cheeks. As I read it I recalled the time a journalist falsely quoted me, to suggest that I “came up with the idea of figs being a keystone”. Sixteen years later those words still make me wince, for they made it seem I had stolen another scientist’s idea. In fact it was Professor John Terborgh, then of Princeton University, who had been the first biologist to apply Paine’s keystone concept to fig trees.
The journalist had interviewed me in 1997 for The Reporter, a newsletter for staff and postgraduate students at the University of Leeds, because I had won a prize in the Daily Telegraph Young Science Writers competition with an article about fig trees. While I am certain Professors Terborgh and Paine never saw the piece, I remember well the horror I felt when I read the words the journalist had put into my mouth. The experience would guide me well in my own journalism years later.
Now, thanks to the memories Ed’s article has triggered, I’d like to set the record straight and also publicise a vast dataset that nearly got lost and which explains why figs are so special. I can trace its origins back through the work of both John Terborgh and Bob Paine.
Here too is the story I wrote that got The Reporter‘s journalist all worked up. Please forgive its naivety and clunky construction — it was my first ever attempt to write about science for a non-technical audience and it is clear to me today that I was still writing then as a scientist.
Some months later, on 18 February 1998, The Daily Telegraph published it with the title ‘Answering the distress call’. I prefer the title I submitted at the time — the one I have used for this blog post.
Figs: A job for conservation’s keystone cops
It is a myth that in tropical forests the bounty of nature’s larder is available year round to support fruit-eating animals. In reality, they may experience alternating episodes of feast and famine, with fig-eating potentially meaning the difference between life and death.
Many tropical fruit-bearing plants share seasonal fruiting patterns, with one or two peaks of ripening at the same time each year. Fig trees, though, can fruit at any time and, so, many sustain fruit-eaters through lean times. As well as providing for the vertebrates, figs may ensure the survival of more rarely fruiting species by maintaining animals which disperse their seeds. By attracting seed dispersing animals, figs may also be instrumental in the recolonisation of deforested areas, or volcanic islands.
Ecologists have described figs as keystone resources in tropical forests. Just as the removal of a keystone of an arch is quickly followed by its collapse, the loss of ecologically important keystone species may trigger a cascade of local extinction.
With more than 800 diverse species, fig plants exhibit great variety — including trees, climbers, shrubs, bushes, epiphytes and tree-stranglers. More so than any other wild tropical fruit, figs provide a large dietary contribution for a veritable Noah’s Ark of animal species. With varying colour, design and position, figs attract different types of vertebrates. The weird and wonderful mix of fig-eaters includes: fish, lizards, giant tortoises, birds, fruit bats, monkeys, rodents, bearded pigs, spectacled bears and the oddly-named olingos, kinkajous and binturongs.
Year-round fruiting is good news for the fruit-eaters, especially as fig trees produce superabundant crops (up to one million figs) and have only short intervals between fruiting episodes. The best documented of fruit shortages is the 1970-71 famine on Barro Colorado Island (BCI), Panama, where in the eight months from July 1970, fewer than 50 per cent of potentially productive plant species bore fruit. Intense hunger stress among fruit-eaters resulted in so many deaths that vultures could not cope with the supply of corpses. Starvation declined suddenly when figs came to the rescue — with peak fruiting in January and February 1971.
More recent research has identified a possible keystone role of figs in Peninsular Malaysia, Borneo and Peru’s Amazon basin where Princeton University’s John Terborgh suggests that loss of figs could lead to ecosystem’s collapse. However, at other sites in Gabon and India figs are apparently less important — being present at low densities and feeding only a small proportion of fruit-eaters. The importance of fig species evidently varies (to misquote George Orwell, “some figs are more equal than others”) either due to their distribution, density and crop size, or as a consequence of animals’ abilities to locate and utilise the fig resource.
Ecologists need to act as “keystone cops” to identify which fig species are disproportionately important in tropical forests with rollercoaster fruit economies. This requires exhaustive fieldwork, encompassing studies of fruiting patterns of figs and other species and behavioural studies of fruit-eating animals.
In Shakespeare’s Antony and Cleopatra, one of the queen’s attendants declares, “I loved long life better than figs.” Tropical fruit-eaters may be able to enjoy both, living longer through their love of figs. If some fig species are show to have keystone importance, their protection may be vital to tropical animal communities. This conservation goal is not too far out of reach as to be unrealistic.
In re-typing these words, I’m pleased to note how much I would write it differently today. I’m amazed too that I managed to wrote about figs being important to wildlife without mentioning the fig-wasps that are the reason for that — see The humbling history of the tiny wasps that upset a Jurassic Park narrative.
The article I wrote back in 1997 won me subscriptions to Nature and New Scientist. Later on it helped me secure funding for a PhD and get my first two jobs outside of academia. It was a real keystone in my career.
Like so many of the researchers Ed Yong highlighed in his Nature piece, I owe some words of thanks to Bob Paine, the man whose starfish throwing days set so many biological balls rolling. As Ed notes in his blog Paine is a keystone too.
I took a stroll in Hanoi today*. It’s a beautiful city. But parked motorbikes and perched purveyors of foods and goods possess its pavements. So to walk one must step into the streets and have faith in the swirling mass of motorists whose pulse keeps the city alive.
The constant sounds of their car and motorcycle horns beep and parp and wahdah-wahdah-wa-wa without pause. They tear the air and probably save lives, but they also kill a bit of a wanderer’s pleasure by drowning out other noises.
The only birdsong I heard today came from bulbuls and babblers and magpie-robins that hung from storefronts in little wooden cages. There’s an irony in their lonely captivity because Hanoi is also a city of trees, a city of fig trees that owe their existence to the some of the same species whose caged members no longer fly free.