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More Testosterone Means More Foot Wiggling for These Frogs

Picture this: you’re out at a bar, and you’ve just met a real cutie. You stand up to order another round, but when you turn around, you see that some jerk has moved in on your date. The bar is so loud that yelling to get their attention won’t do you much good. What do you do? Well, if you want to take the tactic of a male Bornean rock frog, you should start aggressively waving one of your feet. Researchers have found that the frogs’ “foot-flagging” behavior is linked to testosterone levels. They published their research in the Proceedings of the National Academy of Sciences

The Bornean rock frog (Staurois parvus) is a small amphibian that makes its home in the island’s lush rainforests. S. parvus is especially fond of hanging out near thundering waterfalls, which makes for beautiful views but a whole lot of ambient noise. However, mating season necessitates certain types of communication. To work around this, S. parvus and a few other species have started using a sort of natural semaphore system, in which a male frog waves his specialized white-webbed back foot around like a flag. 

To other male frogs, a foot-flag is a clear sign of macho aggression. So researchers wondered if macho hormones—in this case, testosterone—might be involved in the process.

"We know that testosterone is an important regulator of many types of sexual behaviors, so it seems a natural hypothesis that this steroid might also influence waving by affecting the motor systems that control physical movement,” Matthew Fuxjager, Wake Forest University biologist and co-lead-author of the paper, said in a press statement.

To find out, Fuxjager and his colleagues selected 40 male Bornean rock frogs from a rainforest-like terrarium at the Vienna Zoo. The researchers looked for males who showed clear territorial behaviors, including foot flagging.

These males were split into experimental and control groups. Frogs in the experimental group were given a small injection of testosterone in saline solution. Those in the control group just got the saline. As soon as the frogs had gotten their treatment, the researchers paired them up: either two experimental-group frogs or two control-group frogs. Each pair was placed in a mesh container, where they were soon joined by a female frog. The mesh container was then placed in a large habitat with a waterfall, to replicate the environment the frogs find most romantic. To increase the realism, the researchers also played them audio of other frogs croaking.

The frogs were given an hour to get used to their new digs. Then, the researchers switched on a video camera and left it trained on the frog trio for seven hours. After all the frogs had gone through the experiment, a researcher, who didn’t know which frogs were which, watched the tapes and took notes on the frogs’ foot flagging and croaking.

The scientists killed six males, as well as six each of two related, non-foot-flagging species (Rana pipiens and Xenopus laevis). They then used RNA testing to examine the makeup of the animals’ thigh muscles, brains, spinal cords, and larynxes.

The results showed that testosterone did indeed affect S. parvus frogs’ bodies and their aggressive behavior. The thigh muscles of S. parvus specimens contained 10 times more male-hormone receptors than those of the other species. In other words, the Bornean frogs’ legs were ready to be pumped up. And the testosterone definitely pumped them up; the S. parvus males in the experimental group were much more likely than control-group frogs to start waving their legs around.

"These data therefore suggest that the evolution of the foot flag is associated with a dramatic change in how hormones act on specific muscles in the body, particularly those muscles that control the display in the first place," Fuxjager said. "These findings provide novel insight into how the evolutionary gain of a sexual display trait may be augmented by evolution of the hormone systems that control and refine adaptive motor skills."

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Animals
7 Fun Facts for Elephant Appreciation Day
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Happy Elephant Appreciation Day! Celebrate the occasion with some facts about everyone's favorite gentle giant. 

1. ELEPHANTS CAN RECOGNIZE OTHER ELEPHANT CARCASSES.

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The University of Sussex's Karen McComb told National Geographic that elephants "become excited and agitated if they come across a dead elephant," and, in particular, will investigate skulls and tusks. McComb teamed up with researchers at the Amboseli Elephant Research Project in Kenya to study the behavior, showing wild elephants a range of objects that included skulls. They found that the elephants examined skulls—and tusks in particular—of their own kind twice as long as other skulls, and examined tusks six times as long as they did pieces of wood. They were even able to recognize elephant skulls with the tusks removed, but didn't show preference for certain elephant skulls over others, which suggests they didn't know which skulls belonged to their own relatives. "Animals that are intensely social in life may be most likely to display an interest in their dead," McComb told National Geographic. "But what goes on in their minds while they are doing this is a total mystery."

2. THEY'RE SCARED OF BEES.

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Forget about mice scaring off elephants: When farmers need to keep elephants away from their crops, they should use bees. Researchers in Kenya discovered that even the recorded sound of buzzing bees was enough to make elephants retreat—and cause them to emit a low-frequency sound, inaudible to humans, that warns other elephants of the bees' presence.

"It's impossible to cover Africa in electric fences," Lucy King, author of the paper, told The Huffington Post. "The infrastructure doesn't exist in many places and it would restrict animals' movement." But something like a bee fence—hives strung on strong wires a certain distance apart that would move when elephants walked into them, disturbing the hives—"could be a better way to direct elephants away from farmers' crops," she said.

3. THEY MIGHT UNDERSTAND POINTING.

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Humans often use pointing as a way to nonverbally get a message across, though not many other animals grasp the concept. But according to a two-month study of 11 tame African elephants, these pachyderms might be able to: When presented with two identical buckets and pointed in the direction of the one containing food, elephants picked up on the cue fairly consistently: Elephants had a success rate of 67.5 percent (1-year-old humans have a success rate of 72.7 percent). But an earlier study of Asian elephants indicated that they don’t notice pointing gestures, which is a bit of a mystery.

4. ONE ELEPHANT CAN "TALK." 

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Koshik, an elephant in a South Korean zoo, developed the ability to imitate the sounds of five words he's heard from his trainer—annyeong (hello), anja (sit down), aniya (no), nuwo (lie down), and joa (good)—by sticking his trunk in his mouth. The scientists who first noticed Koshik’s ability speculate that he learned to “talk” because he was lonely.

5. THEY'RE DIGITIGRADES.

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It's Latin for "finger walking," and what it means is that elephants walk on their toes (there are five of them, as well a sixth false toe). According to the book Mammal Anatomy: An Illustrated Guidemost of the animals' weight "rests on a broad pad of elastic tissue behind the toes" which "acts as a shock absorber and prevents the skeleton from jolting too much when the animals walk. It also allows elephants to move surprisingly quietly despite their size."

6. AN ELEPHANT PREGNANCY LASTS ABOUT TWO YEARS.

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If you thought being pregnant for nine months was a long time, be glad you're not an elephant, which can be pregnant for up to 680 days, according to the BBC. All that time in the oven has a benefit, though: Elephant calves are born with highly-developed brains, capable of learning their herd's complex social structures and ready to put their trunks to use.

7. NINETY-SIX ELEPHANTS ARE KILLED IN AFRICA EVERY DAY.

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Unfortunately, elephant poaching remains a very big problem: An estimated 35,000 elephants are killed annually, their tusks sold illegally in the ivory market. Do the math, and that comes out to nearly 96 elephants every day. Find out what you can do to help elephants and stop poaching at 96Elephants.org.

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Bumblebees Mark Their Trails With Tiny Scented "Footprints"
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Yani Dubin via Flickr Creative Commons // CC BY-ND 2.0

Bees seem to have an endless number of tricks up their sleeve—and on their feet. Scientists have discovered that bumblebees leave itty-bitty scented “footprints” on every flower they visit, thereby informing other foragers that the bloom’s been recently tapped. The researchers published their findings in the journal Nature Scientific Reports.

Bees are the queens of complex communication. They exchange information with one another and their environments using a dazzling array of sensory input, including electrical impulses, sound, dance, and chemical signals.

Some of those signals flow out into the world through the bees’ delicate little feet. The bottom segment of a bee’s leg, called the tarsus, secretes a scented goo that helps the bee stick to the soft surfaces of flower petals. The chemical profile of each bee’s foot-glue is as unique as a fingerprint.

Previous studies have shown that bees glean important information from one another’s goo, skipping flowers that other bees have already visited. This raised an interesting question: If a bee can "read" another bee’s scent mark, can it also identify that bee?

To find out, researchers planted small clusters of fake flowers in the laboratory and topped some of them up them with sucrose nectar. They then gave bumblebees (Bombus terrestris) free rein to tromp around the blossoms, marking them up and taking in the marks of other bees that had come before.

The bees proved careful and canny readers. Not only did they use other bees’ scent marks to decide which flowers to probe, but they also considered the source of the scent when making that decision. An individual bee could easily differentiate between the smell of its own feet (trustworthy), those of its family members (very trustworthy), and those of strangers (not a reliable source of floral information).

Lead author Richard Pearce is a biologist at the University of Bristol. "Bumblebees are flexible learners and, as we have discovered, can detect whether or not it is they or a different bumblebee that has visited a flower recently. These impressive abilities allows them to be cleverer in their search for food, which will help them to be more successful," he said in a statement.

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