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NatureWrap: Dolphins are clever breathers

Dolphins actively slow their hearts before diving and can even adjust their heart rate to suit how long they plan to dive for, a new study suggests.

Researchers from Europe and North America worked with three male bottlenose dolphins (Tursiops truncatus), specially trained to hold their breath for different lengths of time upon instruction.

“We trained the dolphins for a long breath-hold, a short one, and one where they could do whatever they want”, says Andreas Fahlman of Fundación Oceanogràfic, Spain, co-author of a paper in Frontiers in Physiology.

“When asked to hold their breath, their heart rates lowered before or immediately as they began the breath-hold. We also observed that the dolphins reduced their heart rates faster and further when preparing for the long breath-hold, compared to the other holds”.

The results suggest, Fahlman says, that dolphins – and possibly other marine mammals – can vary their reduction in heart rate “as much as you and I are able to reduce how fast we breathe”.

“This allows them to conserve oxygen during their dives, and may also be key to avoiding diving-related problems such as decompression sickness, known as the bends.”

The smell of cooperation

Rats are known to be sociable and quite altruistic. Now researchers have now shown that they just have to smell the scent of another that is engaged in helpful behaviour to increase their own helpfulness.

The test of character. Credit: Michael Taborsky

A team from the universities of Göttingen (Germany), Bern (Switzerland) and St Andrews (Scotland) ran a series of tests in which a rat could choose to pull a platform containing food towards another rat’s cage. The pulling rat would get no immediate benefit from helping.

At the same time, the rats were presented with the smell of either a rat that was being helpful in a different room or a rat that was not engaging in helpful behaviour.

“Test rats increased their own helping behaviour when they were presented with the smell of a helpful rat,” says Göttingen’s Nina Gerber. “Remarkably, this holds true even though they did not experience this helpful behaviour themselves.”

This “smell of cooperation” depends on the actual activity of helping and is not connected to an individual rat. There isn’t a “special smell” for certain nice rats: the same individual can release the scent of being helpful or not, depending solely on their behaviour.

The findings are published in the Proceedings of the Royal Society B.

Jaguars under pressure

Wild jaguars in the Amazon can cope with climate extremes in the short term but numbers will rapidly decline if weather events increase in frequency and food sources are diminished, a new study has found.

A team led by Kerrie Mengersen and Kevin Burrage from Australia’s QUT gathered data from a field trip to the remote Pacaya Semiria Reserve in Peru and a census study based on camera traps and scat analysis, jaguar ecology and knowledge of Indigenous rangers.

They then analysed six scenarios mapping the creature’s solitary behaviour, mating, births of cubs at certain times of the year, competition, illegal hunting, death from starvation and availability of key prey. In the worst-case scenario, the estimated jaguar population of 6-700 would drop to single figures in 30 years, Burrage says.

The jaguar (Panthera onca) is the dominant predator in Central and South America and is considered a near-threatened species by the International Union Conservation Nature.

The study’s findings are published in Ecology and Evolution.

Researcher Kerrie Mengersen using a drone during studies in the Amazon. Credit: QUT Media

Wings that don’t just fly

British researchers say they have discovered the precise wing construction that has enabled moths to evade their most troublesome predators.

Using an array of analytical techniques, including airborne cross-sectional imaging, acoustic-mechanics and refractometry, a team from the University of Bristol found that the very thin scale layer on the wings has evolved ultrasound-absorptive properties that provide acoustic camouflage against echolocating bats.

“Such a broadband absorption is very hard to achieve in the ultrathin structures of moths’ wings, which is what makes it so remarkable,” says sensory ecology expert Marc Holderied.

It also goes well beyond the limits attainable with classical porous absorbers of the kind currently used to absorb sound in office environments, which use thick materials, the researchers write in the journal PNAS.

The composite image below shows the moth Antheraea pernyi (top) and butterfly Graphium agamemnon with a photograph on the left and ultrasound echo image (tomography) on the right.  The moth wing has weaker echoes (acoustic image) than the butterfly wing.

Credit: Marc Holderied and Thomas Neil