Stripping Down Science (15 page)

In fact, what they saw was that the injury provoked nearby surviving mature heart cells to temporarily shed their muscle-cell-like appearance, resembling stem cells instead.
These cells then began to divide, producing replacement muscle cells, all of which bore the coloured genetic marker. The regenerating cells also turned on another gene called gata4, which is normally active during embryonic development of the heart, suggesting that the heart muscle repairs by reactivating the same genetic program that was used to build the heart in the first place inside the embryo. Working out how to make a damaged human heart do the same is therefore a major priority for researchers worldwide.

A commonly held myth is that the sea is blue because it reflects the colour of the sky. In fact, it's the strange chemistry of water that gives the sea its colour, and has also led some underwater species to evolve the fish equivalent of an infrared spy camera.

Water is one of the most abundant molecules on the earth. Most of it arrived here from space in the form of ice aboard comets that have rained down on the earth over the four and a half billion years since the planet first formed. Geologists have calculated that there's almost one and a half billion cubic kilometres of water on earth, and without it life would probably never have got off the ground, or even off the seabed, in the first place.

That's because water has some unusual chemical properties. Each molecule, formula H
₂
O, resembles a tiny boomerang with the oxygen atom at the apex and the hydrogen atoms at each of the tips. This structure soaks up light in the part of the spectrum that we feel as heat, or infrared,
which is why water vapour in the atmosphere is actually a more powerful greenhouse gas than carbon dioxide. In this respect, it helps to keep the planet warm.

But in the ocean, where water molecules are surrounded by many other water molecules, a phenomenon called hydrogen bonding occurs. Put simply, these are weak ‘intermolecular forces' that arise because water is what's known as a ‘polarised molecule'. The central oxygen (O) of the H
₂
O pulls the electrons of the two hydrogens towards itself, making the hydrogens slightly positively charged and the oxygen slightly negative. Since unlike charges attract, a hydrogen on one molecule will be attracted to the oxygen of another adjacent water molecule. This makes water sticky and accounts for many of its wonderful life-sustaining properties.

The consequence of this hydrogen bonding is that it makes the molecules ‘stiffer', so when light hits water, instead of absorbing just in the infrared, it begins to absorb more strongly at visible red wavelengths too. Since more red wavelengths are being soaked up, leaving behind relatively more blue light, the water looks blue. And the deeper you go, the greater the amount
of red light that has been removed, so the ‘bluer' everything looks. In fact, at depths over a few hundred metres, only a very narrow range of visible wavelengths can make it through, and these are entirely at the blue end of the spectrum. As a result, many of the marine species that live at these depths lack the necessary chemicals in their eyes to even ‘see' red light, leading scientists to believe that this was true of all these animals.

But therein lies another myth, because marine biologists recently stumbled upon some fish species that have turned this disability into a weapon.
⁴⁹
The deep-sea stomiid dragon fishes
Malacosteus
,
Aristostomias
and
Pachystomias
have evolved an organ that sits beneath their eyes and pumps out red light. The fish have also altered their retinae, adding a number of extra light-detecting chemicals. These adaptations mean that the fish can see both their own and the red light produced by other members of the same species, while other fish remain oblivious to the fact that they are being ‘spotlighted' and possibly eyed up for dinner. They are, quite literally, left in the dark. Apart from hunting, however, this covert communications system also makes light work of seeing potential predators before they see you, and in finding a mate, which puts a whole new spin on the idea of a red light district …

Bees are universally viewed as shining examples of hard workers who also dance for their dinner: when one bee finds a fruitful food source, just like motorists tipping each other off about low-cost fuel, the discoverer returns to the nest where she performs an intricate ‘waggle dance' to inform hive-mates where to fly so they too can get nectar and pollen on the cheap. Previously, scientists thought that was the ‘bee-all' and end-all of the story, but now it turns out to be something of a myth, because researchers have discovered that there's a flip side to the waggle dance: a flight-deterrent manoeuvre that takes the form of a headbutt.

Originally, bee researchers believed this behaviour was a begging call for food. But James Nieh, a San Diego-based scientist,
⁵⁰
has scratched that claim by watching the behaviour of bees
returning to their hives after being attacked during foraging flights by members of rival bee colonies. He noticed that if a bee that had recently been mugged by rivals during one of its food-gathering flights spotted another bee using its waggle dance to recruit other workers to forage in the same potentially lethal location, the bruised bee would start headbanging the dancer to make her stop.

Slowed down to make it easier to see, the movement actually consists of the sender of the signal butting her head into the recipient and then vibrating her body 380 times per second for about one-tenth of a second. This neutralises the dance and alerts the performing bee to the fact that she could be leading the hive off in a potentially dangerous direction, so she stops.

Moreover, the bees seemed to have a greater gift for risk assessment than an OH&S inspector. Nieh noticed that the number of times the stop signal was issued by an individual was proportional to the level of danger it had faced previously when foraging. Survivors of ‘significant aggression' – presumably the bee equivalent of ‘did you spill my beer?' – upped their rate of warnings 40-fold, while others that had their legs mechanically pinched with tweezers to simulate
a bite from another bee delivered 88-fold more warnings. ‘Butt' what's the point of this insect manifestation of health and safety?

The answer is that nature tends to work in a push-pull fashion. The waggle dance is one way that bees can ‘push' each other to venture after certain food sources but, unchecked, this could mean they all end up directing each other into a disaster. So the headbutt-transmitted stop signal serves as a way to rein in the risk. It effectively ensures that the response the colony makes to a threat is proportional to the level of danger it faces.

According to James Nieh, ‘This signal is directed at bees who are recruiting for the dangerous food location and decreases their recruitment,' he says. ‘Thus, fewer nest-mates go to the dangerous food site. This is important because an individual experiences danger and stops recruiting herself, but the stop signal also enables her to “warn” other recruiting nest-mates too. The end result is that the colony will reduce or cease recruitment to the dangerous food patch in proportion to the threat.'

So bees, it seems, don't just dance for their dinner, they also headbutt their way out of danger!

FACT BOX

What is the waggle dance?

The bee waggle dance was first decoded in the 1960s by the Austrian Nobel prize winning ethologist Karl von Frisch.
⁵¹
He christened this unique bee language ‘Tanzsprache' and undoubtedly it's one of the wonders of the insect world and what helps to make bees so successful as a social species. In general terms, it works rather like a news grapevine, allowing foragers to share with sister bees information about the direction and distance to food sources or potential new homes.

So what's involved? Rather like 1980s break-dancers on the street, bees perform the waggle dance in front of any other bees who'll stop and watch. Dancing bees move in a figure-of-eight pattern comprising a ‘waggle run' followed by a turn to the right to take them back to the starting spot, then another waggle run followed by a turn to the left, again returning
them to the starting point. Most dances last for 100 such circuits and are accompanied by a waft of chemical signals from the dancer's abdomen to make other workers pay attention.

The direction of the waggle run indicates the direction other bees should fly in, relative to the position of the sun, and the distance is communicated by the duration of the waggle phase of the dance: every 75 milliseconds of dance duration translates into a flight of 100 metres. The bees can also take into account the passage of time and use their body clocks to predict the movement of the sun across the sky to avoid becoming disorientated.

But not all bee observers are quick on the uptake: some are too stubborn to be told, others will cotton on after watching just a few dances, some need a bit more nurturing, while others fly off in a totally different direction despite their education. Pretty similar to humans, really!

Fertile as the oceans are, if land becomes contaminated with salt it can spell disaster for crops, which shrivel up and die. But fruitful research from Australia now looks set to turn salt toxicity into a marine myth.

Salt is bad for land-based plants because when the plant takes up water from the soil, dissolved salts are drawn in too and make their way up to the leaves. When the water then evaporates from the leaf surface into the surrounding air, the salt is left behind and accumulates. A small amount of salt is tolerable, but if the levels become too high they cause the leaves and shoots to age prematurely. This means that, rather like a loan-shark victim struggling to cover the interest on a mounting debt, the plant ends up investing most of its energy just trying to repair and replace damaged tissue rather than growing effectively.