August 19, 2009

Sex Secrets Of The Flying Fox

The male flying fox with higher levels of testosterone in its blood has a better shot at keeping its roost of picky females, according to a study.

This connection can only be observed during breeding season, according to the report published in the Royal Society journal Biology Letters.

Biologists say that understanding the reproduction and behavior of these bats could better enable conservation efforts. 

These little Casanovas have an incredible sex drive. They begin copulating weeks before conception is even possible. First, the males begin by actually increasing in size as hormonal levels increase.

They then start vigorously marking their territory and defending it from other males. Once the male selects his female of the day, he copulates with her repeatedly, the frequency increasing as they get closer to the time of conception. Their rigorous foreplay and sexual positions would put the Kama Sutra to shame. 

The group of researchers studied grey-headed flying foxes, also called fruit bats, that live in colonies of up to 20,000 animals.

"This species is in decline," said lead author Stefan Klose from the University of Ulm in Germany. "And flying foxes disperse seeds so they're really important for ecosystems."

Dr Klose and his colleagues observed a colony of the flying foxes in New South Wales, Australia.

"In these colonies you see flying foxes hanging everywhere - it looks absolutely random, but that's not the case," Dr. Klose told BBC News.

"Every meter of branch that you see is someone's territory. And within that [male's] territory, there is a group of females. The size of that group depends on the attractiveness of the male."

The number of females in each male's harem were counted by Dr. Klose and his team and then they caught a group of males by using a special device to take the bats from their branches.

"We kept the males in captivity for three days, and during that time we took a blood sample to determine the testosterone levels," explained Dr Klose.

"Then we released the males back into the colony and watched where they went."

During the mating period, males with high testosterone were better able to reclaim their harems.

"This was when all the mating took place - when it really mattered," said Dr. Klose.

He went on to explain that the primary male sex hormone testosterone causes the bat to become more aggressive. Therefore, the males with higher testosterone levels are going to have more confrontations with other males.

"If you can afford high testosterone because you're strong and you're very healthy, then you're able to reap the benefits," explained Dr Klose. "So you will potentially get a lot of females in your territory and have a lot of offspring."

It also seemed that the males with a larger territories were more popular with the ladies,  possibly serving as a "quality indicator".

"It's all about female choice," Dr Klose said. "So you could imagine that the females think that if a male is able to defend a large territory in an attractive location, he must really be a hotshot."

He strongly emphasized the importance of the information in terms of conservation efforts, since it is common to try to relocate the colonies away from residential areas.

"People use smoke and noise to drive them away, because they perceive them as noisy or stinky," said Dr Klose. "But when we released our males, all of them returned to their colonies."

Ignacio Moore, an animal behavior scientist from Virginia Tech in the US, who was not involved in this study, described it as "a nice example of basic physiology and behavior being useful for conservation".

"The implication is that relocating the animals during the breeding season will not work, as they will simply return," he told BBC News.

"Suitable habitat must be made available before the breeding season for the animals to inhabit."

Elizabeth Atkins-Regan, a biologist from Cornell University in Ithaca, New York, said that age might also play a role in the male's ability to sustain its harem.

"Perhaps older males have higher testosterone and also are more successful at regaining harems," she said.

"It's hard to know whether the higher testosterone is the cause of the greater success, or whether success is due to something else like experience. I very much hope the authors will continue this research to find out whether there is a causal relationship."


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