The Chinese soft-shelled turtle looks like someone glued the snout of a pig onto the face of a fish, with the texture of a scrotum for good measure. But its bizarre appearance pales in comparison to an even more bizarre, and newly discovered, habit: it expels waste through its mouth.
When the turtle breaks down proteins in its liver, it ends up with an abundance of nitrogen, which it expels from its body in the form of urea. Humans are the same—we get rid of urea in the form of urine, via our kidneys. But the soft-shelled turtle has an altogether different route.
It’s well-adapted to life in the water, and lives in salty swamps and marshes. But Yuen Ip from the National University of Singapore noticed that when the turtle emerges from water, or is stranded on land during dry spells, it will plunge its head into puddles. While submerged, it rhythmically expands and contracts its mouth. Ip found that the turtle gets rid of most of its urea through its mouth rather than its kidneys, via gill-like studs in its mouth. It can breathe and get rid of waste through the same structures.
[Update: Note the comments below. Urine is more than just dissolved urea, so while the stuff the turtle spits out is similar, it’s not quite the full deal.]
In North America’s Sonoran desert, there’s a fly that depends on a cactus. Thanks to a handful of changes in a gene called Neverland, Drosophila pachea can no longer make chemicals that it needs to grow and reproduce. These genetic changes represent the evolution of subservience – they inextricably bound the fly to the senita cactus, the only species with the substances the fly needs.
The Neverland gene makes a protein of the same name, which converts cholesterol into 7-dehydrocholesterol. This chemical reaction is the first of many that leads to ecdysone – a hormone that all insects need to transform from a larva into an adult. Most species make their own ecdysone but D.pachea is ill-equipped. Because of its Neverland mutations, the manufacturing process fails at the very first step. Without intervention, the fly would be permanently stuck in larval mode. Hence the name, Neverland—fly genes are named after what happens to the insect when the gene is broken.
Fortunately, in the wild, D.pachea can compensate for its genetic problem by feeding on the senita cactus. The cactus produces lathosterol—a chemical related to cholesterol. D.pachea’s version of Neverland can still process this substitute, and uses it to kickstart the production of ecdysone.
The senita is the only plant in the Sonoran desert that makes lathosterol, the only one that lets the fly bypass the deficiency that would keep it forever young. It has become the fly’s dealer, pushing out chemicals that it cannot live without, and all because of changes to a single fly gene.
Here’s the tenth piece from my BBC column
Humans have to grow, hunt, and gather food, but many living things aren’t so constrained. Plants, algae and many species of bacteria can make their own sustenance through the process of photosynthesis. They harness sunlight to drive the chemical reactions in their bodies that produce sugars. Could humans ever do something similar? Could our bodies ever be altered to feed off the Sun’s energy in the same way as a plant?
As a rule, animals cannot photosynthesise, but all rules have exceptions. The latest potential deviant is the pea aphid, a foe to farmers and a friend to geneticists. Last month, Alain Robichon at the Sophia Agrobiotech Institute in France reported that the aphids use pigments called carotenoids to harvest the sun’s energy and make ATP, a molecule that acts as a store of chemical energy. The aphids are among the very few animals that can make these pigments for themselves, using genes that they stole from fungi. Green aphids (with lots of carotenoids) produced more ATP than white aphids (with almost none), and orange aphids (with intermediate levels) made more ATP in sunlight than in darkness.
Another insect, the Oriental hornet, might have a similar trick, using a different pigment called xanthopterin to convert light to electrical energy. Both insects could be using their ability as a back-up generator, to provide energy when supplies are low or demand is high. But both cases are controversial, and the details of what the pigments are actually doing are unclear. And neither example is true photosynthesis, which also involves transforming carbon dioxide into sugars and other such compounds. Using solar energy is just part of the full conversion process.
There’s a bizarre mindset that divides medicine into “natural” (made from plants; untainted by villainous pharmaceutical companies; delivered to your veins by forest animals) and everything else (“man-made” pills fashioned from profits and poisons). The reality, of course, is that many of the drugs used in our hospitals and pharmacies come from plants. Willow bark contains salicylic acid, the main ingredient in aspirin. Paclitaxel (taxol) was isolated from the bark of the Pacific yew tree; today, it is used to stop cancer cells from dividing. The rose periwinkle has given us vinblastine and vincristine, both used to treat leukaemia.
These examples scratch the surface of what the botanical world has given us, and what it might still offer. Of the tens of thousands of plants used in “traditional medicine”, a piddling proportion has been tested for chemicals with medical benefits. How do we find the rest? How do we go about the business of “bioprospecting”? One solution is to tap the knowledge of indigenous populations, who still rely on plants for traditional medicine. When they get sick, how do they heal themselves?
But this approach has problems. Traditional use doesn’t always imply an actual medical benefit, and the chosen plants might not yield interesting chemicals any more readily than the species around them. Many attempts to follow such leads have ended in the drug-development cul-de-sac. To make matters worse, collating traditional knowledge involves fieldwork and training, and is both expensive and time-consuming.
Meanwhile, the tools of molecular biology have become faster and cheaper. Companies can afford to gather large collections of plants, and screen their constituent chemicals en masse. Why filter them any further when you can test thousands of samples at once? But Haris Saslis-Lagoudakis from Imperial College London thinks that this scattershot approach to bioprospecting is a mistake. To him, traditional knowledge still has great value in honing our search for tomorrow’s drugs.
In the forests of central Africa, there’s a plant that looks like it’s growing its own Christmas decorations. Shiny baubles sprout from between its leaves, shimmering in a vibrant metallic blue. Look closer, and other colours emerge – pinpricks of red, orange, green and violet. It looks as if Seurat, or some other pointillist painter, had turned their hand to sculpture.
But these spheres, of course, are no man-made creations. They’re fruit. They are the shiniest fruits in the world. Actually, they are the shiniest living materials in the world, full-stop.
They belong to a plant called Pollia condensata, a tropical metre-tall herb that sprouts its shiny berry-like fruits in clusters up to 40-strong. These little orbs are iridescent – they use special layers of cells, arranged just so, to reflect colours with extraordinary intensity. This trick relies on the microscopic physical structures of the cells, rather than on any chemical pigments. Indeed, the fruits have no blue pigment at all.
In the animal kingdom, such tricks are commonplace – you can see them at work on the wings of a butterfly, the shells of jewel beetles, or the feathers of pigeons, starlings, birds or paradise and even some dinosaurs. But in the plant world, pigments dominate and structural colours
were thought to be non-existent are much rarer.
Words like “individual” are hard to use when it comes to the black cottonwood tree. Each tree can sprout a new one that’s a clone of the original, and still connected by the same root system. This “offspring” is arguably the same tree – the same “individual” – as the “parent”. This semantic difficulty gets even worse when you consider their genes. Even though the parent and offspring are clones, it turns out that they have stark genetic differences between them.
It gets worse: when Brett Olds sequenced tissues from different parts of the same black cottonwood, he found differences in thousands of genes between the topmost bud, the lowermost branch, and the roots. In fact, the variation within a single tree can be greater than that across different trees.
As Olds told me, “This could change the classic paradigm that evolution only happens in a population rather than at an individual level.” There are uncanny parallels here to a story about cancer that I wrote last year, in which British scientists showed that a single tumour can contain a world of diversity, with different parts evolving individually from one another.
I learned about Olds’ study at the Ecological Society of America Annual Meeting and wrote about it for Nature. Head over there for the details.
Photo by Born1945
If you’ve ever bitten into a wild tomato, you’ll have enjoyed a sweet, intense explosion of flavour. The tomatoes that line most supermarket shelves are a world apart. They look great – a wall of even, ripe red – but they taste like cardboard. These two facts are related.
Ann Powell from the University of California, Davis has found that farmers have inadvertently ruined the taste of tomatoes by selecting for ones that ripen together and look good. That aesthetic appeal has been driven by a single change in a single gene, which also affects how the fruits taste.
Flesh-eating plants are basically nitrogen thieves. The speed of their growth is limited by this invaluable element, just like all other plants. The difference is that plants that eat animals, like pitcher plants and the Venus fly trap, grow in places like swamps and rocky outcrops, where nitrogen in thin on the ground… or thin in the ground. They have to supplement their supply by stealing nitrogen from the bodies of animals. This is why some plants become killers.
Let me clarify that: this is why some plants become obvious killers. Scott Behie from Brock University has found that a far greater range of plants can inconspicuously assassinate animals by proxy. They partner up with an infectious fungus that kills insects and transfers their precious nitrogen to the plant. Thanks to the fungi, the plants become indirect predators.
A desert mouse has found a seed. It bites into it, and gets a pungent mouthful of mustard. Reeling from the chemical party in its mouth, its spits out the seed and unwittingly helps the seed’s producer – a Israeli desert plant called Ochradenus baccatus. By using chemical weapons, it converts rodents into an unwitting vehicles for its seeds.
Ochradenus produces yellow flowers and sweet, succulent, white berries. When a mouse bites into the berries, an enzyme in the seeds called myrosinase mixes with chemicals in the pulp called glucosinolates. Housed in their separate compartments, these substances are harmless. But when they are released by gnawing teeth, and mix together, the enzyme converts glucosinolates into a wide range of toxins. These include isothiocyanates, the substances that give mustard and wasabi their pungent kick. As the mouse breaks the berries, an explosion of mustard goes off in its mouth.
Michal Samuni-Blank from the Technion–Israel Institute of Technology in Israel filmed the spitting mice using motion-activated cameras in the Israeli desert. The mice would carry away clusters of fruit to eat them in sheltered rocky crevices. Once they got a mouthful, they spit out more than two-thirds of the pungent seeds. If Samuni-Blank treated the seeds to deactivate their stash of myrosinase, the mice ate more than 80 per cent of them.
It’s a rainy day in the jungles of Borneo, and an ant has taken shelter from the falling drops by clinging to the underside of a leaf. It has chosen poorly. Its shelter is the ‘lid’ of a pitcher plant, and it hangs over a living vase full of digestive fluids. As rain pummels the jungle, a drop lands on the lid and flicks off the ant underneath. The insect falls into the pool of fluid and is consumed by the plant.
Pitcher plants are famous for their flesh-eating ways, and they rely on slippery surfaces to trap their prey. Its pitcher-shaped traps are made from rolled up leaves, and secrete nectar from their rims to entice their prey. During wet conditions, the rims are coated with a thin layer of water, making them extremely slippery. They have another trick too – tapering wax crystals on the inner walls of the pitcher. These greatly reduce the surface area that insect feet would cling to, and ensure that individuals that fall inside can’t climb back out.