You might not be that impressed to receive a clump of grass or branches on a first date, but a boto dolphin might think differently. A new study suggests that these Amazonian dolphins wave bits of flotsam to attract mates.
The boto is a freshwater river dolphin that swims through the currents of the Amazon and the Orinoco. They are elusive creatures that are difficult to study, so very little is known about their social lives.
Tony Martin from the University of St Andrews spent three years in the Amazonian Mamiraua reserve studying the behaviour of botos. During this time, he spotted over 200 groups of dolphins playing with objects, a behaviour that other scientists have noted throughout the animals’ range and was recently filmed in the “Fresh Water” episode of Planet Earth.
The botos pick up branches, sticks, vegetations and lumps of clay in their mouths, often thrashing them against the water surface or throwing them with jerks of the head. None of the objects are edible and the carriers often swim in a ritualised way, spinning slowly with their head above the water.
Bad experiences can be powerful learning aids for our sense of smell. A new study reveals that electric shocks can make people more sensitive to the differences between very similar chemicals that previously smelled identical.
Every day, thousands of different molecules waft past our nose. Many of these are uncannily similar and some are more important to others. Wen Li from Northwestern University wanted to see how people learn to distinguish the critical smells from the unimportant ones.
Smell the difference
Working in the lab of smell guru, Jay Gottfried, Li attempted to train 12 volunteers to smell the difference between a pair of enantiomers – molecules that are mirror-images of each other but are otherwise identical. The two chemicals were versions of 2-butanol and both had a grassy tang. At first, Li asked volunteers to sniff the odd one out between three bottles, two that contained one molecule and a third that contained its mirror-image. On average they scored 33%, no more accurate than complete guesswork.
Their scores more than doubled when Li gave the volunteers an electric shock whenever they were exposed to one enantiomer, but not the other. Li didn’t provide any shocking impetus for a second pair of mirror-image molecules and accordingly, this control pair remained indistinguishable throughout the experiment.
Imagine that you hand is made of jelly and you have to carve a roast using a knife that has no handle. The bare metal blade would rip through your hypothetical hand as easily as it would through the meat. It’s clearly no easy task and yet, squid have to cope with a very similar challenge every time they eat a meal.
The bodies of squid, like those of their relatives the cuttlefish and octopus, are mainly soft and pliant, with one major exception. In the centre of their web of tentacles lies a hard, sharp and murderous beak that resembles that of a parrot. The beak is a tool for killing and dismembering prey and the large Humboldt squid (Dosidicus gigas) is known to use its beak to sever the spinal cord of fishy prey, paralysing them for easy dining.
The Humboldt squid’s beak is two inches long and incredibly hard (difficult to dent or scratch), stiff (difficult to bend out of shape) and tough (resistant to fractures). This combination of properties makes the beak harder to deform than virtually all known metals and polymers. That’s all the more remarkable because unlike most animal teeth or jaws, it contains no minerals or metals. It’s made up solely of organic chemicals and manages to be twice as hard and stiff as the most competitive manmade equivalents.
By comparison, the mass of muscle that surrounds and connects to the beak is incredibly soft, the equivalent of a jelly hand gripping a bare metal blade. With such mismatched tissues, how does the squid manage to use its killer mouth without tearing the surrounding muscle to shreds?
My first ever feature article has just been published in this week’s issue of New Scientist. It’s about the ways in which songbirds are coping with the noisy din of cities. Low-frequency urban noises mask the calls that they use to attract mates, defend territories and compete with rivals. The race to adapt to this new soundscape has already seen some losers being forced out and some winners developing some intriguing strategies to cope with the clamour.
Robins have started to sing at night when it’s quieter, while nightingales just belt out their tunes more loudly (breaking noise safety regulations while they’re at it). Several species including great tits and song sparrows have started to sing at higher frequencies that are less likely to be masked. Song is a sexual trait, and over time the different strategies used by urban and country birds could lead to a single species splitting into two.
That’s a little taster of the full article, which I’m not allowed to publish here. You’ll need a subscription to New Scientist to read the whole shebang online. I’m really excited about this – I’ve been trying to pitch a feature for them for about a year now, and I prefer the experience to writing news pieces.
Would you gamble on a safe bet for the promise of something more? Would you risk losing everything for the possibility of greater rewards? In psychological experiments, humans tend to play it safe when we stand to gain something – we’re more likely to choose a certain reward over a larger but riskier one. Now, we’re starting to understand how our two closest relatives deal with risk – bonobos, like us, tend to be risk-averse while chimpanzees usually play the odds.
Sarah Heilbronner from Harvard University studied the attitudes of five chimps and five bonobos to risky decisions. All the animals had been born in captivity in the Liepzig Zoo, Germany and were fed well on a regular schedule. Heilbronner presented the apes with one of two upside-down bowls of different shapes and colours. One ‘fixed’ bowl always contained four grape pieces and the other ‘variable’ one had a fifty-fifty chance of concealing either one grape piece or seven.
After a few trials with each bowl to get them accustomed to the options, Heilbronner let the animals choose between the two. The chimps were most likely to take a gamble on the variable bowl and they only chose the fixed one 36% of the time. The bonobos on the other hand mostly liked to play it safe and picked the fixed bowl 72% of the time. On an individual level, all of the five bonobos showed risk-averse behaviour and four of the five chimps demonstrated a penchant for risk-taking.
It’s not that one of the two species learns about the choice more slowly than the other; the differences in their behaviour were apparent in the very first trials of the experiment, and only grew larger with experience. Nor was it the case that either chimps or bonobos had better mathematical skills than the other. When they were offered the bowls face-up and could see what was inside, they almost always picked the one with the most grape pieces.
We’ve all seen the images of receding glaciers and stranded polar bears that accompany talks of climate change. But rising carbon dioxide levels also have subtler and less familiar effects, and may prove to be a boon for many animal groups. Plant-eating insects, for example, have much to gain in a high -CO2 future as rising concentrations of the gas can compromise the defences of the plants they feed on.
Plants and herbivorous insects are engaged in a silent war that we are rarely privy too, where chemicals act as both weapons and messengers. Munching mandibles trigger the production of signalling molecules like jasmonic acid that announce the presence of invaders to other plants of the plant, neighbouring individuals, or even parasitic wasps, which attack the pests and turn them into living larders for wasp eggs.
The battle isn’t over even after parts of the plant are eaten. Beetles, for example, rely on enzymes called cysteine proteinases to digest the plant proteins they swallow, and free up valuable amino acids for the insects’ own growth. But when plants detect jasmonic acid signals, they produce chemicals called “cysteine proteinase inhibitors” (CystPIs) that block the insects’ digestive enzymes and prevent them from fully digesting their meals.
But these defences may buckle as carbon dioxide levels rise. Jorge Zavala and colleagues at the University of Illinois found that increasing levels of CO2 reduce the ability of soybeans to use jasmonate signals. That shrinks their stockpiles of defensive CystPIs and makes them more vulnerable to hungry pests including two voracious species of beetle – the western corn rootworm (Diabrotica virgifera) and the Japanese beetle (Popillia japonica). Given that soybeans are an increasingly important food crop, it’s in our interest to stop insects from eating them so that we can instead.
Bdelloid rotifers are one of the strangest of all animals. Uniquely, these small, freshwater invertebrates reproduce entirely asexually and have avoided sex for some 80 million years. At any point of their life cycle, they can be completely dried out and live happily in a dormant state before being rehydrated again.
This last ability has allowed them to colonise a number of treacherous habitats such as freshwater pools and the surfaces of mosses and lichens, where water is plentiful but can easily evaporate away. The bdelloids (pronounced with a silent ‘b’) have evolved a suite of adaptations for surviving dry spells and some of these have had an unexpected side effect – they’ve made the bdelloids the most radiation-resistant animals on the planet.
Ionising (high-energy) radiation is bad news for living cells. Far from granting superpowers, it damages DNA, often completely breaking both strands of the all-important molecule. If you think of DNA as a recipe book for the various parts of a living thing, the double-stranded DNA breaks that are caused by ionising radiation are like tearing the book up into small chunks.
Absorbed doses of radiation are measured in Grays and ten of these are more than enough to kill a human. In comparison, bdelloids are a hundred times harder. Eugene Gladyshev and Matthew Meselson from Harvard University found that two species shrugged off as much as 1,000 Grays and were still active two weeks after exposure.
About a month ago, I migrated from the safe, stable climate of WordPress to the unknown but promising habitat of ScienceBlogs. With four weeks having flown by, this seems like a good a point as any to have a bit of a navel-gazing retrospective about what’s changed since the move.
Eagles may be famous for their vision, but the most incredible eyes of any animal belong to the mantis shrimp. Neither mantises nor shrimps, these small, pugilistic invertebrates are already renowned for their amazingly complex vision. Now, a group of scientists have found that they use a visual system that’s never been seen before in another animal, and it allows them to exchange secret messages.
Mantis shrimps are no stranger to world records. They are famous for their powerful forearms, which can throw the fastest punch on the planet. The arm can accelerate through water at up to 10,000 times the force of gravity, creating a pressure wave that boils the water in front of it, and eventually hits its prey with the force of a rifle bullet. Both crab shells and aquarium glass shatter easily.
As impressive as their arms are, the eyes of a mantis shrimp are even more incredible. They are mounted on mobile stalks and can move independently of each other. Mantis shrimps can see objects with three different parts of the same eye, giving them ‘trinocular vision’ so unlike humans who perceive depth best with two eyes, these animals can do it perfectly well with either one of theirs.
Their colour vision far exceeds our too. The middle section of each eye, the midband, consists of six parallel strips. The first four are loaded with eight different types of light-sensitive cells (photoreceptors), containing pigments that respond to different wavelengths of light. With these, the mantis shrimp’s visible spectrum extends into the infrared and the ultraviolet. They can even use filters to tune each individual photoreceptor according to local light conditions.
The fifth and six rows of the midband contain photoreceptors that are specialised for detecting polarised light. Normally, light behaves like a wave that vibrates in every possible direction as it moves along. In comparison, polarised light vibrates in just one direction – think of attaching a piece of string to a wall and shaking it up and down. While we are normally oblivious to it, it’s present in the glare that reflects off water and glass and we use polarising filters in sunglasses and cameras to screen it out.
Light can also travel in a the shape of a helix, moving as a spiralling beam that spins either clockwise (right-handed) or anti-clockwise (left-handed). This phenomenon is called ‘circular polarisation’. Tsyr-Huei Chiou from the University of Maryland found that the mantis shrimp’s eye contains the only known cells in the animal kingdom that can detect it. Our technology can do the same, but the mantis shrimps beat us to it by as much as 400 million years.