Panda dung hormones reveal sex secrets

Giant panda in Foping Nature Reserve (Image: Fuwen Wei) Foping Nature Reserve has one of the densest panda populations in China

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Yong-Gang Nie, an ecologist from the Chinese Academy of Sciences, spent a total of 150 days battling through sleet, snow and thick bamboo. All to collect excrement.

But this is very special excrement; the young researcher has been collecting giant panda droppings.

The droppings have revealed important clues about the sex lives of these mysterious and endangered animals.

These findings are reported in the European Journal of Wildlife Research.

Mr Nie, and his colleague Prof Fuwen Wei, focused on the population of 50-70 pandas in Foping Nature Reserve - one of the densest panda populations in China.

They have been tracking the animals, as well as taking hormone and DNA samples from their droppings.

Researcher Fuwen Wei examining a sample of panda dung (Image: Fuwen Wei) The researchers search through dense bamboo forests for the excrement

The hormone they are interested in is testosterone. By testing the dung for this hormone, the scientists have shown how pandas' sex lives are influenced by dramatic spikes in a chemical that puts male pandas "in the mood".

Their most surprising conclusion is that pandas appear to conserve their hard-earned energy by keeping testosterone levels relatively low until they have found a female.

This is linked to the fact that the bamboo the animals eat gives them relatively little energy. It is so nutritionally poor that the bears have to consume about 20kg per day to take in enough calories.

The team thinks that poor nutrition could be to blame for the failure to breed many captive pandas.

The Chinese researchers teamed up with ecologist Ronald Swaisgood, director of animal ecology at San Diego Zoo, California, US. They planned to study the wild pandas' mating habits, and to use these findings to help improve captive breeding programmes.

Dr Swaisgood, also a panda specialist, says that the animals are not the fumbling, sexually incompetent beasts that many people believe them to be.

"I really want to dispel this myth that pandas don't know how to mate or have problems mating," Dr Swaisgood told the BBC's Science in Action programme, "because left to their own devices, they do just fine.

"They live in areas where there's plenty of bamboo and if that environment is left intact they do well.

"Our findings with wild pandas suggest that poor nutrition and as a consequence low testosterone could contribute to mating failure in captive breeding programs."

Testosterone-fuelled

Start Quote

As soon as the female comes into heat and they gather around that female - boom - the testosterone spikes”

End Quote Ronald Swaisgood San Diego Zoo

Pandas are quiet and usually solitary animals; they are difficult to find, which makes them arkward to study.

So Prof Wei and his team fitted two male pandas in Foping with satellite-tracking collars, which have enabled the scientists to locate and observe the secretive animals.

Following and observing these pandas revealed that, when a female was "in heat", males gathered around her to compete for a chance to mate.

"That's when they get quite noisy, so that's another way we can find them," explained Dr Swaisgood.

"We go up on the mountains or the ridges there and we listen for these groups of pandas that have got together for mating."

Testosterone is what triggers much of this aggression and friskiness. The hormone essentially makes animals amorous, so the researchers wanted to gather enough hormone-laced panda dung to find out how the males' testosterone levels fluctuated during the breeding season.

"This is an animal that defecates almost 50 times per day, so they leave behind a trail of these goodies for us to collect," said Dr Swaisgood.

Careful examination of panda droppings has revealed that the animals experience surprisingly brief hormonal spikes during the breeding season.

"We had predicted for pandas that they should show a seasonal rise in testosterone," said Dr Swaisgood. "They should just crank up the testosterone... for the whole season.

"But they're living on the edge energetically.

"They have to eat a lot of bamboo... and bamboo quality is at its lowest point right before the mating season."

On top of this inconveniently timed food shortage is the fact that testosterone is very "energetically expensive".

"The hormone cranks up your whole system and makes you burn more energy," Dr Swaisgood explained.

From the hormone levels they detected in the panda dung, the researchers realised that, to cope with this, the animals "waited" to find a female that was in heat before boosting their testosterone levels.

"As soon as the female comes into heat and they gather around that female - boom - the testosterone spikes," Dr Swaisgood explained.

In pandas, male testosterone levels seems to be linked directly to the social environment.

"Our data suggest," said Dr Swaisgood, "that pandas are too low on energy in the mating season to afford the costly side-effects of testosterone on their energy stores."

To allow captive male pandas this necessary spike in testosterone levels, Dr Swaisgood says that breeding programmes need to be acutely aware of nutrition. Frisky pandas need ample food supplies.

"Pandas fed a poor diet or [that] were otherwise in poor body condition may not sustain testosterone levels sufficient for breeding," he explained to BBC Nature.

"Historically, when diets were sometimes not as good as they usually are today, many males failed to show interest in females that were clearly ready for mating. I always found this strange."

With the right social environment and the right diet, the scientists think that captive breeding of pandas could be much more successful.

Hear an interview with Dr Ronald Swaisgood on Science in Action on the BBC World Service on Friday 16 September

Follow @BBCNature on Twitter

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