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Howler Monkeys Can Either Be Really Loud or Well-Endowed

Dating is tough. We all know that. To attract the right mate, or any mate at all, you have to stand out from the crowd. Maybe your best quality is your sense of humor, or your twinkling eyes, or your sweet dance moves. Maybe—if you’re a howler monkey—it’s your enormous testicles, or your ability to yell louder than anyone else.

To ensure the continuation of their genes, male howler monkeys invest energy in making noise or making sperm. But scientists say they can’t do both. New analysis from the University of Cambridge finds that for howler monkeys, louder calls equal smaller balls.

The howler monkey is a curious creature, a terrier-sized primate with a tiger-sized roar. The monkeys can only reach about 15 pounds, but their calls are among the loudest on the planet. The males’ bellowing, belching calls serve two purposes: to catch lady monkeys’ attention, and to tell other males to take a hike.

The howler monkeys’ larger-than-life noises are possible thanks to a specialized bone called a hyoid. This hollow, pouch-shaped bone acts as an echo chamber, amplifying the calls before they ever leave the monkey’s mouth. The bigger the hyoid bone, the more noise a monkey can make.

This is more important for some species than others, and it all comes down to sex. Some howler monkeys have harem-type setups, where one male monkey mates with several female monkeys. In those arrangements, the challenge lies in appealing to the ladies and keeping other dudes away, but once mating has taken place, a male monkey can be pretty sure his sperm are safe.

Other species have a more relaxed sex scene in which female monkeys are free to take as many mates as they want. For these species, the males with the biggest cojones—and thus the most sperm—are the ones most likely to succeed in making monkey babies.

But yelling and making sperm each require a lot of energy. The monkeys can’t have their yelling and big balls, too.

These are the conclusions of a new paper published this week in the journal Current Biology. Researchers used 3-D laser scans to measure the hyoid bones and testes of 10 species. They found a distinct inverse relationship between the two. Harem-type species had larger hyoid bones and smaller testes, and the reverse was true for the free-love-type species. Exactly how this trade-off happened is not totally clear, lead author Jacob Dunn said in a press release.

“In evolutionary terms,” Dunn said, “all males strive to have as many offspring as they can, but when it comes to reproduction you can’t have everything.”

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Animals
25 Shelter Dogs Who Made It Big
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Focus Features

If you’ve been thinking of adding a four-legged friend to your brood and are deciding whether a shelter dog is right for you, consider this: Some of history’s most amazing pooches—from four-legged movie stars to heroic rescue dogs—were found in animal shelters. In honor of Adopt-a-Shelter-Dog Month, here are 25 shelter dogs who made it big.

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technology
This High-Tech Material Can Change Shape Like an Octopus
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Octopuses can do some pretty amazing things with their skin, like “see” light, resist the pull of their own sticky suction cups, and blend in seamlessly with their surroundings. That last part now has the U.S. Army interested, as Co.Design reports. The military branch’s research office has funded the development a new type of morphing material that works like an octopus’s dynamic skin.

The skin of an octopus is covered in small, muscular bumps called papillae that allow them to change textures in a fraction of a second. Using this mechanism, octopuses can mimic coral, rocks, and even other animals. The new government-funded research—conducted by scientists at Cornell University—produced a device that works using a similar principle.

“Technologies that use stretchable materials are increasingly important, yet we are unable to control how they stretch with much more sophistication than inflating balloons,” the scientists write in their study, recently published in the journal Science. “Nature, however, demonstrates remarkable control of stretchable surfaces.”

The membrane of the stretchy, silicone material lays flat most of the time, but when it’s inflated with air, it can morph to form almost any 3D shape. So far, the technology has been used to imitate rocks and plants.

You can see the synthetic skin transform from a two-dimensional pad to 3D models of objects in the video below:

It’s easy to see how this feature could be used in military gear. A soldier’s suit made from material like this could theoretically provide custom camouflage for any environment in an instant. Like a lot of military technology, it could also be useful in civilian life down the road. Co.Design writer Jesus Diaz brings up examples like buttons that appear on a car's dashboard only when you need them, or a mixing bowl that rises from the surface of the kitchen counter while you're cooking.

Even if we can mimic the camouflage capabilities of cephalopods, though, other impressive superpowers, like controlling thousands of powerful suction cups or squeezing through spaces the size of a cherry tomato, are still the sole domain of the octopus. For now.

[h/t Co.Design]

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