22 June 2013 | NewScientist | 17

Prehistoric fish had world’s first abs

ABDOMINAL muscles are such a good idea they evolved at least twice. Specialised stomach muscles were thought to be unique to land animals, but new fossils show that they also evolved earlier in ferocious armour-plated fish.

The fossils reveal that placoderms, a group of early jawed fish, had strips of muscle running across their stomach as well as the muscles running the length of the body that most fish possess (Science, doi.org/mvn).

“We were stunned to find that our ancient fossil fishes had abs,” says Kate Trinajstic of Curtin University in Perth, Australia, who led the research along with Per Ahlberg of Uppsala University in Sweden.

Nobody knows why the placoderms had abdominal muscles like these. Ahlberg says it might be due to the rigid armour covering the front halves of their bodies. As the placoderm swam, waving its tail from side to side, the lighter rear half of its body would have swung from side to side as well without additional bracing, creating powerful shearing forces. Perhaps the abdominal muscles worked to keep this from happening.

Donate your heartbeat for an out-of-body experienceA LIVE video of your body appearing to pulse in time with your heartbeat can trigger an out-of-body experience.

We can identify with a virtual body in a different location to our own if we are fed conflicting information via senses such as vision and touch. Researchers at the Swiss Federal Institute of Technology in Lausanne wondered whether the experience could also be triggered by playing with signals from within our own bodies – interoception. They asked 17 people to stand wearing a

headset which showed themselves being filmed from behind, so that they essentially saw their own back 2 metres in front of them.

Software created a halo effect around this virtual body, with the halo flashing either in time with their heartbeat or slightly out of step – although volunteers were not told this was the case. After 6 minutes, the volunteers closed their eyes and were guided backwards. They were then asked to move to where they felt they had been standing.

Participants performed well

HOW can you warn others around you of danger? If you’re a giant honeybee, the answer is jarringly simple: create the bee equivalent of an earthquake.

The 2-centimetre-long insects build a flat comb attached to the lower surface of a tree branch or a rocky overhang. Each side of the nest is carpeted with seven or eight layers of bees, forming a “bee curtain”.

When a predator approaches, the bees on the side facing it send out a warning by waving their abdomens, creating a miniature Mexican wave. But it wasn’t clear how this would be picked up on the far side of the nest.

Gerald Kastberger of the University of Graz in Austria and his colleagues wondered whether the Mexican wave might send a signal right through the nest, alerting bees without a visual lock on the predator.

The team simulated an attack on a nest and used a laser to track what happened. The Mexican wave caused the comb to vibrate at about 2 hertz, which should allow bees on the other side to sense it.

“This is a nice way to bring information from one side to the other,” says Kastberger (Naturwissenschaften, doi.org/mt3).

Nest quakes alert bees to danger

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when the halo flashed out of sync with their pulse. But when it was in sync, they moved close to the position of their virtual body. This suggests their feeling of being “anchored” within their own body had been altered (Psychological Science, in press).

Thomas Metzinger of the Johannes Gutenberg University in Mainz, Germany, is impressed: “It tells us that human self-consciousness is anchored in interoception in a much stronger way than people have acknowledged before.”

Oyster shells stall in acidic water

ACIDIFYING oceans are pitting newborn oysters in a race against time to build their shells.

Recent studies have shown that oyster larvae are significantly less likely to survive as seawater pH falls. To find out why, George Waldbusser’s team at Oregon State University in Corvallis studied oyster larvae during their first three weeks of development.

They found that they undergo a growth spurt during the first 48 hours of life, forming new shell 10 times faster than at five days old.

This spurt is fuelled by nutrients packed into each larva’s egg. As well as powering shell construction, the nutrients also fuel the development of feeding organs – vital for getting energy once the food source from the egg has been used up. But such high growth rates are difficult to sustain when seawater pH falls. That’s because the carbonate ions normally used to build calcium carbonate shells instead react with the increased number of hydrogen ions in acidic seawater (Geophysical Research Letters, doi.org/mts).

The study is an “excellent example” of researchers going beyond documenting which species are vulnerable to acidification and instead asking why and when the problems will emerge, says Geraint Tarling at the British Antarctic Survey in Cambridge, UK.

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