Plant lures bats with echoing leaf

Flowers use bright colours and striking patterns to attract pollinators that are guided by sight, such as bees and hummingbirds. So it makes sense that plant species pollinated by bats, which are guided by sound, should entice them in a similar way.

Now scientists from the UK and Germany have proved the point for the first time. They have discovered a Cuban rainforest vine – Marcgravia evenia – that grows a dish-shaped leaf just above each flower, to send back conspicuous echoes to nectar-feeding bats. As a result, the bats find its flowers twice as fast by echolocation as they would otherwise.

By analysing the leaf’s acoustic reflection properties, the researchers found that it acts as an ideal beacon, sending back strong, multidirectional echoes with an easily recognisable acoustic signature – perfect for making the flower obvious to echolocating bats.

The scientists then trained nectar-feeding Glossophaga soricina bats to search for a single small feeder hidden within an artificial foliage background, varying the feeder’s position and measuring the time the bats took to find it. The feeder was presented on its own, or with a replica of either an ordinary foliage leaf or the distinctive dish-shaped leaf.

Search times were longest for all bats when the feeder was presented on its own, and were very slightly shorter when a foliage leaf was added. However, a dish-shaped leaf placed above the feeder always reduced the bats’ search times – by around 50 per cent.

Although the leaf’s unusual shape and orientation mean that it is less efficient at photosynthesis than an ordinary leaf, the cost is outweighed by the benefits of more efficient pollinator attraction. The leaf and its flower stand out from the chaotic stream of echoes being reflected back to squeaking bats from nearby rustling plants.

“This echo beacon has benefits for both the plant and the bats,” says Dr Marc Holderied of Bristol University, a co-author of the study, published in the journal Science. “On one hand, it increases the foraging efficiency of nectar-feeding bats, which is of particular importance, as they have to pay hundreds of visits to flowers each night to fulfil their energy needs. On the other hand, the Marcgravia evenia vine occurs in such low abundance that it requires highly mobile pollinators.”

Bats, with their wide home range and excellent memory, are efficient pollinators and many other tropical plants depend on them. As the acoustic and perceptual principles shaping the echo beacon leaf of Marcgravia evenia should work for all echolocating pollinators, the researchers expect to find other instances of plant species that use acoustic signalling to attract their bat pollinators.

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Banks risk all by sticking together

The 2008 financial crisis and its aftermath have stimulated research aimed at better scientific understanding of banks and their risks of failure, drawing on insights from fields such as ecology, epidemiology and engineering.

The latest work, by a UK-US group, appears in Proceedings of the National Academy of Sciences. It highlights the “regulator’s dilemma” – that making individual banks safer may increase the risk of disaster for the financial system as a whole.

“We use a simple model to illustrate an idea that, on reflection, people understand instinctively,” says David Rand of Harvard University’s evolutionary dynamics programme. “When many banks do the same thing, simultaneous bank failures become very likely.”

An individual bank may believe that it is pursuing a low-risk strategy through diversification – but the systemic risk will be magnified if all big banks diversify in the same way, the authors say.

“You want the banks to be diversified, but in different ways, so that the conditions that would cause one bank to fail would be different from the conditions that would cause another bank to fail,” Rand says.

Regulators should therefore promote “diverse diversification”, encouraging each bank to pursue a risk strategy distinct from its competitors.

The authors are putting their conclusions to banks and regulators, who are thinking much more about the stability of financial systems as a whole than they were before the crisis.

“We believe this can be achieved without a central authority directing the banks in particular areas,” says Nicholas Beale, director of Sciteb, a London strategy consultancy.

A regulatory scheme could give an incentive to systemic diversity, by basing the amount of capital a bank is required to hold on the extent to which its investment strategy contributes to systemic risk.

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Calorie listings work – but only for a few

The controversial law in New York City that forces fast-food restaurants to post calorie counts on menus has had limited – but real – success in persuading diners to eat less fattening meals.

A study of the 2008 law, one of the first in the world to tackle the obesity epidemic by putting nutritional information on menus, shows that only one customer in six uses the calorie counts – but this minority responds by ordering meals with lower energy content.

The study, published in the British Medical Journal, analysed the orders of 15,800 customers in 168 fast-food outlets before and after the law took effect. On average, the 15 per cent who used the calorie counts ate 106 kilocalories fewer per meal than the majority who ignored the information.

Although there was no statistically significant decline in calories purchased across the whole survey sample, three big chains saw appreciable reductions: by around 6 per cent at McDonald’s and KFC, and 14 per cent at Au Bon Pain. In contrast, energy content increased by 17 per cent at Subway, where large portions such as the $5 foot-long sandwich were promoted.

Obesity affects more than 30 per cent of adults and 17 per cent of children in the US. In an accompanying editorial, Susan Jebb of the MRC Human Nutrition Research Centre in Cambridge adds that, in the UK, “sustained improvements in diet will require a transformation of the food supply too”.

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One (small) quantum leap in data processing

The promise of quantum computing – exploiting the strange rules of quantum physics rather than conventional electronics – will only become a reality if scientists can find a way to cut through the immense complexity of the circuitry required.

A research team based at Bristol University has taken an important step in that direction, by discovering and testing a new way to control the algorithms – instructions for carrying out mathematical operations – in quantum computers.

Such computers work with quantum bits, or “qubits”, which can function in several states at the same time – unlike the bits in today’s computers, which are either on or off. As a result, quantum computers should be able to hold and process a much larger amount of data much more quickly than their conventional counterparts.

Professor Jeremy O’Brien, director of Bristol’s Centre for Quantum Photonics, and his colleagues have discovered how to add “control qubits” to any quantum operation, thereby greatly simplifying the circuits that are required for the computer to work.

“The new approach could be the most important development in quantum information science over the coming years,” says O’Brien, whose research is published in the journal Nature Communications.

“It provides a dramatic reduction in quantum circuit complexity – the major barrier to the development of more sophisticated quantum algorithms – just at the time that the first quantum algorithms are being demonstrated.”