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.
When I last spoke to John Rogers from the University of Illinois, we talked about his new “electronic skin” – a patch that can be applied like a temporary tattoo, that monitor heartbeats and brain activity, and that flexes and bends without breaking. We talked about his curved camera, inspired by the human eye. We spoke about his flexible medical sensors that can mould to the contours of a beating heart or the fissures of a human brain. We chatted about the $500,000 MIT-Lemelson prize that he had won for his inventions.
I tell you all this because I want you to understand that when John Rogers says his team’s new invention is “some of our best stuff ever”, he’s not speaking lightly.
Rogers has now created a line of “transient electronics”, which last for a specified amount of time before completely dissolving away. Having made his name by taking rigid and brittle electronics and making them flexible and bendy, he has now flipped durability on its head too. Electronics are typically engineered to last as long as possible, but Rogers wants to create machines that will disintegrate after a given time. And his team have already shown how this disappearing tech could be used to make medical implants that are absorbed by the body after their work is done.
Medical implants are an obvious application, and the one that led them down this road in the first place. They have already been working on flexible sensors that can be implanted into the brain and heart, to monitor for signs of epilepsy or heart attacks. “The thing you bump up against is how to get these things to survive in the body for a long time without adverse effects,” says Rogers. “One way to deal with that problem is to move around it. A lot of these implants don’t need to last forever.”
When Marvel Comics created a short superhero who could heal horrific injuries, perhaps instead of “Wolverine”, they should have named him “African spiny mouse”. These tiny rodents can jettison strips of skin from their own hides when captured by predators, and heal those same wounds with extraordinary speed.
Healing powers are common in the animal world. Salamanders and starfish can regrow lost limbs, while some flatworms can regenerate their bodies from a single cell. But mammals lag behind – while some species can grow back a lost tail, when most of us lose our body parts, we do so permanently. The spiny mice are an exception.
Biologists have noted that these rodents have very weak skin, which seems to slough off easily when they are handled. Led by these anecdotal reports, Ashley Seifert from the University of Florida has studied the skin-shedding ability in greater depth, focusing on two species: Kemp’s spiny mouse (Acomys kempi); and Percival’s spiny mouse (Acomys percivali).
In 2010, an article in Rolling Stone likened the investment bank Goldman Sachs to “a great vampire squid wrapped around the face of humanity, relentlessly jamming its blood funnel into anything that smells like money.”The creature it was referring to does exist – it’s not a true squid, but one of their close relatives. But despite its terrifying name and appearance, it’s not a vampire. It doesn’t suck blood. It doesn’t have a “blood funnel”.
In fact, thanks to newly published observations, we now know that the vampire squid is a garbage-eater. It extends living fishing lines from its body to snag a rain of rubbish falling from the surface, getting fat on a menu of faeces and corpses.
The Goldman Sachs metaphor still works, doesn’t it?
The vampire squid belongs to the cephalopods, the group that includes squid, octopuses and cuttlefish. But it’s an evolutionary relict that appeared well before any of these more familiar animals. Its body is gelatinous and blood-coloured, as if the internal organ of a larger animal had broken free. It swims with two wing-like flaps, sees with opal-blue eyes, and lights up the surrounding water with flashing organs found all over its body, and especially at the tips of its arms.
Two of these arms have been modified into white thin filaments, which coil up into special pockets, and can extend to 8 times the animal’s length. The other eight arms are connected by a cloak-like web that can be inverted over the vampire squid’s body to reveal a muddy charcoal interior, lined with fleshy spines. You can see where the name comes from.
The vampire squid lives all over the world, but we know very little about what it does. That’s partly because it lives at incredible depths – 600 to 900 metres below the surface, in pitch blackness. This level is known as the oxygen minimum zone (OMZ) and unlike the vampire squid, it’s well-named. While a few animals thrive here, most are choked off by the lack of oxygen.
The vampire squid copes by having an incredibly slow metabolism, blood proteins that hug oxygen molecules with an unyielding grip, and a body that so closely matches the density of water that it neither floats nor sinks. It rarely wastes energy on unnecessary movements. It simply hangs in the darkness.
But even though it lives life in the slow lane, the vampire squid needs food, and that’s in short supply in the oxygen minimum zone. What does it eat? To find out, Hendrik Hoving and Bruce Robison from the Monterey Bay Aquarium Research Institute (MBARI) analysed footage of 170 vampire squids, taken over the last decade by the institute’s submersibles.
The videos, along with feeding experiments on captive vampire squids, revealed that they use their filaments like mobile spider webs. They extend these into the surrounding water to ensnare particles of food falling from above. The filaments are covered in tiny hairs, probably for catching these particles. They also have neurons that connect to a particularly large part of the creature’s brain, presumably so it can sense what’s stuck to its fishing lines.
When the time is right, it retracts the filaments, transfers the food to its other arms, and coats them in mucus secreted from its arm tips. It then conveys these delicious balls of mucus-bound detritus into its mouth, possibly with the help of the spines within its cloak.
This strategy is very different to that of other cephalopods, most of which are active hunters that attack and kill their food. Vampire squids are definitely not that, as Hoving and Robison confirmed by checking the stomachs of captured specimens. They found eggs, algae, pellets of faeces, bits of jelly, crustacean body parts—antennae, eyes, some shells, whole copeopods—and flesh from another deep-sea squid. In both kind and quantity, these remnants don’t reflect the diet of a hunter.
Instead, Hoving and Robison think that the vampire squid is mainly a ‘detritivore’ – a rubbish-eater. With few predators in the oxygen minimum zone, it can afford to sacrifice powerful swimming muscles or a high metabolism. Instead, it leads a relatively passive lifestyle, collecting the plentiful snowing debris with its two modified arms. With these adaptations, it can greatly extend the reach of its mouth, while its body—and its life—literally hangs in the balance.
Reference: Hoving & Robsion. 2012. Vampire squid: detritivores in the oxygen minimum zone. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2012.1357
All images from Hoving and Robison
More on cephalopods
Here’s the 11th piece from my BBC column
On Friday, 11 March 2011, an earthquake struck the oceans near Tohoku, a region on Japan’s east coast. With a magnitude of 9.0, it was among the five most powerful earthquakes ever recorded, strong enough to shift the entire planet by several inches along its axis. It triggered a tsunami that killed thousands of people and wrecked the Fukushima-Daiichi nuclear power plant.
A quake that large shouldn’t have happened at Tohoku, at least not to the best of Japanese scientists’ knowledge. The hazard maps they had drawn up predicted that big earthquakes would strike in one of three zones to the south of the country – Tokai, Tonankai, and Nankai. No earthquake has hit these regions since 1975, while several have occurred in “low-probability” zones, such as Tohoku.
Japan isn’t alone. The incredibly destructive earthquakes that hit Wenchuan, China in 2008 and Christchurch, New Zealand in 2010 and 2011 all happened in areas deemed to be “relatively safe”. These events remind us that earthquake prediction teeters precariously between the overly vague and overly precise. At one extreme, we can calculate the odds that big earthquakes will strike broad geographic areas over years or decades – that’s called forecasting. At the other extreme, early warning systems can relay news of the first tremors to people some distance away, giving them seconds to brace themselves. But the ultimate goal – accurately specifying the time, location and magnitude of a future earthquake – is extremely difficult.
The cheetah’s spots look like the work of a skilled artist, who has delicately dabbed dots of ink upon the animal’s coat. By contrast, the king cheetah – a rare breed from southern Africa – looks like the same artist had a bad day and knocked the whole ink pot over. With thick stripes running down its back, and disorderly blotches over the rest of its body, the king cheetah looks so unusual that it was originally considered a separate species. Its true nature as a mutant breed was finally confirmed in 1981 when two captive spotted females each gave birth to a king.
Two teams of scientists, led by Greg Barsh from the HudsonAlpha Institute for Biotechnology and Stanford University, and Stephen O’Brien from the Frederick National Laboratory for Cancer Research have discovered the gene behind the king cheetah’s ink-stains. And it’s the same gene that turns a mackerel-striped tabby cat into a blotched “classic” one.
Back in 2010, Eduardo Eizirik, one of O’Brien’s team, found a small region of DNA that seemed to control the different markings in mackerel and blotched tabbies. But, we only have a rough draft of the cat genome, they couldn’t identify any specific genes within the area. The study caught the attention of Barsh, who had long been interested in understanding how cats get their patterns, from tiger stripes to leopard rosettes. The two teams started working together.
Our lives are governed by both fast and slow – by quick, intuitive decisions based on our gut feelings; and by deliberate, ponderous ones based on careful reflection. How do these varying speeds affect our choices? Consider the many situations when we must put our own self-interest against the public good, from giving to charity to paying out taxes. Are we naturally prone to selfishness, behaving altruistically only through slow acts of self-control? Or do we intuitively reveal our better angels, giving way to self-interest as we take time to think?
According to David Rand from Harvard University, it’s the latter. Through a series of experiments, he has found that, on average, people behave more selflessly if they make decisions quickly and intuitively. If they take time to weigh things up, cooperation gives way to selfishness. The title of his paper – “Spontaneous giving and calculated greed” – says it all.
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.