Box jellyfish may lack a brain, but they still make use of two dozen eyes. Now it seems that some of these eyes serve a surprising purpose: helping the jellyfish to navigate using landmarks above the water.

Box jellyfish, , typically live in tropical mangrove swamps, where their crustacean prey abound. We know that their impressive suite of eyes help the animals – but , a biologist at Lund University in Sweden, and colleagues have just discovered that a heavy gypsum crystal embedded in the structures surrounding the eyes keeps some of them pointing directly upwards, no matter how the animal is oriented.

To try to find out why the animals constantly look up, Nilsson and his team placed box jellyfish in a clear, open-top tank, lowered it into a mangrove swamp in Puerto Rico, and monitored the animals with a video camera. When the tank was a few metres from the canopy edge, and the canopy could still be seen directly overhead, the jellies repeatedly bumped into the wall closest to the trees.

Landmark trees

But when the tank was moved 12 metres away from the canopy edge – and the trees were no longer visible from below the water’s surface – the animals swam in all directions. Because the tank kept out chemicals, and jellies can’t discern much under the murky water, Nilsson says they navigate using the trees as landmarks.

“This is the first time terrestrial cues have been demonstrated to be used for navigation by jellyfish or any other invertebrate,” says Nilsson. Staying under the shelter of the canopy will be helpful to the jelly because the crustaceans they eat are found primarily in those shallow waters.

By taking pictures near the surface of the water and modelling what the jellyfish would be able to see using their upper eyes, the researchers confirmed that the animals could detect the trees up to 8 metres from the canopy edge.

The discovery of this advanced visual ability in an animal with a primitive nervous system may surprise some, says , a marine scientist at the University of Texas at Austin. “We have an under-appreciation for how sensory systems in simple organisms are used for fairly sophisticated adaptations.”

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We might know why birds fly south for the winter, but how they achieve the feat is another question – one which we are now beginning to answer.

Each year some 50 billion birds take to the skies to migrate, an often gruelling pilgrimage associated with changes in diet, physiology and behaviour.

To hunt for a genetic basis for those changes, at the Max Planck Institute for Ornithology in Starnberg, Germany, and his colleagues went bird-catching. They trapped birds from 14 populations of the (Sylvia atricapilla), a warbler that spends summer in northern Europe but winters in warmer southern Europe or northern Africa. The birds are typically active only during the day, but they are prepared to fly at night during their migration.

Night-time restlessness

The team recorded and quantified the captive birds’ night-time restlessness – a proxy for migratory behaviour in the wild – and took blood samples to look for genetic signatures that could account for variations in nocturnal activity.

They focused on four genes linked to daily rhythms, changes in which might encourage the birds to migrate at night. Nocturnal restlessness was found to be linked to the gene ADCYAP1. The longer the form of the gene, or allele, the more restless the blackcap.

The gene may do more than simply encourage night-time fidgeting: it encodes a protein called PACAP, which plays a major role in melatonin secretion, energy metabolism and feeding. These functions are crucial for preparing birds for long flights. “This is the first step to bringing research on avian migration down to the molecular level,” says Mueller.

Tip of the iceberg

“It’s a landmark paper,” says at the University of California, Davis. “What remains to be done is to actually silence that gene and see if it affects migratory behaviour.”

at Cornell University in Ithaca, New York, says that the study is the “tip of the iceberg” in understanding the genetic basis for migration. “This is a very important step in a process that’s probably going to take decades to really understand,” he says.

Because the authors analysed DNA sequences that are conserved across species, they will be able to extend their work to other roaming animals. “The race is on to start looking more broadly and cast the comparative net wider,” Winkler says.

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Ever wished you could think more laterally to solve a problem? In future, maybe you’ll just use a bit of mind-boosting technology: zapping the brain with electricity helps people think outside the box to solve a task.

Transcranial direct current stimulation (tDCS) is a safe and non-invasive method of temporarily altering the activity of neurons by passing weak currents through electrodes on the scalp. It can enhance mathematical skills, memory, attention and language learning.

Richard Chi and of the University of Sydney in Australia wondered whether it would help people solve brain-teasers. They began by training 60 volunteers to solve arithmetic problems expressed in Roman numerals constructed from matchsticks. The point of this was to get their brains in the habit of solving problems in a particular way: the participants corrected false calculations by moving matchsticks around to create different numbers.

The volunteers then worked on two further matchstick problems that required a different approach, swapping an equation’s symbols, such as “−” and “÷”, while they received tDCS over their anterior temporal lobes (ATL), brain structures found on each side of the brain near the temples. Chi and Snyder focused their attention on the ATLs because the right-hand one is known to be involved in perceiving the world in a new light.

Some participants received an excitatory current over the right hemisphere of the brain and inhibitory current over the left, while others experienced the opposite pattern or a sham treatment.

Stimulating solution

Excitation of the right hemisphere and inhibition of the left made the participants three times more likely to figure out the correct answer within 6 minutes compared with those who received the sham treatment.

The authors say this result confirms that the right ATL is associated with insight and novel meaning. It also backs up previous findings that the left ATL is involved in processing routine strategies and the maintenance of existing hypotheses. The combination of excitation and inhibition may force participants to examine problems with fresh eyes instead of relying on old routines, say the authors.

“It’s intriguing when brain stimulation leads to improved performance, because typically you find that this type of manipulation is disruptive,” says , a psychologist at the University of California, Santa Barbara.

Schooler says that the tDCS could have disrupted the strategies and cognitive processes used to solve the first set of calculations, and that this helped the subjects switch to a new strategy more effectively. The authors should use additional tasks to determine whether stimulation of the ATL affects other forms of insight, he says.

Journal reference: , DOI: 10.1371/journal.pone.0016655