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Four Different Species Use the Same Odor to Exploit Each Other

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Chemical warfare. Hijacked communications. Stowaways. Eavesdropping. Sounds like the makings of a spy movie, but it’s just another day in nature. 

Plants have got to be fighters in this big bad world. When an animal that wants to eat them comes along to start chowing down, they can’t run or hide. They’ve got to fight back. Some of them have structural defenses like thorns or spines or nettles that jab at herbivores’ mouths. Some have waxy exteriors that make them too slippery for insects to land on, or produce resins and saps that create a sticky trap for bugs.

Others wage chemical warfare, sometimes in a roundabout way. Methyl salicylate (MeSA), also known as wintergreen oil, is produced by some plants when they’re damaged by herbivorous insects. The chemical doesn’t harm the insects directly, but acts like a mayday signal that attracts predatory bugs that come and eat the herbivores. In one case that University of Florida scientists have recently described, it’s also at the center of a web of species trying to exploit each other.

When citrus trees are damaged and release MeSA, it not only attracts helpful bugs, but also a jumping plant louse known as the Asian citrus psyllid (Diaphorina citri, top). The psyllids follow the chemical’s odor because a tree that’s already damaged is a good place to find food, places to lay eggs (which the psyllids can only do in new citrus shoots) and other bugs to mate with. 

Sometimes, though, there’s no meal to be had, because the tree has been infected by a bacterium called Candidatus Liberibacter asiaticus (Las). The psyllids are the bacterium’s primary vector for spreading from tree to tree. When Las infects a tree, it lowers the tree’s nutritional quality and also hijacks its odor production, forcing it to release MeSA as bait. When the psyllids show up and find there’s no less-than-ideal food, they move on in search of another tree—but not before the bacteria cling to them and hitch a ride to their next victim.

A group of entomologists in Florida, led by Xavier Martini, recently found that the trees, lice, and bacteria aren’t using these chemical signals in private, and that there’s another creature eavesdropping on them. The same odor that the lice use to find food, and that the bacteria exploit to lure the lice, also attracts a wasp called Tamarixia radiata. These parasites feed on the bodily fluids of citrus psyllids and also lay their eggs on the undersides of the immature insects. When the eggs hatch, the larvae attach to the psyllid and feed on their hemolymph (kind of the arthropod version of blood) until the host dies. Then, they crawl inside the mummified psyllids, where they’ll develop into adults and eventually break their way back out through the thorax or head. 

Martini and his team discovered that the wasps “eavesdrop” on the chemical cues produced by citrus trees to find their hosts, and were more attracted to the MeSA from Las-infected trees than non-infected trees. At trees where the bacteria was present, the wasps also parasitized five times as many psyllids as they did at the regular trees. 

That the wasps are attracted to the same chemical as the psyllids potentially complicates things for the Las bacteria. Martini found that the wasps sometimes arrive at an infected tree before the psyllids show up, which might drive them away or result in them being killed or parasitized before they can give the bacteria a lift to another tree. Then again, when the wasps show up after psyllids they might actually help the bacteria by causing the psyllids to disperse far and wide, which is exactly what the bacteria need to spread. 

A tree’s “cry for help” not only attracts more danger, but can also be hijacked by bacteria to help them spread infection, while an eavesdropping parasite uses the same odor to find a host that its children turn into a macabre nursery. Ain’t nature grand? 

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Animals
7 Fun Facts for World Elephant Day
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Happy World Elephant 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 low-frequency sound, inaudible to humans, that warns other elephants. "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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Human adults and babies often use pointing as a way to nonverbally get a message across, but 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 bad, 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 herds’ 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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Audible Launches 'Audible for Dogs' to Help Pet Parents Calm Their Stressed Canines
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In addition to a mutual love of hamburgers and lazy sunny afternoons in the backyard, dog owners can now share their affinity for audiobooks with their furry friends. As Fast Company reports, Audible has launched Audible for Dogs, a new service designed to keep canines relaxed while their owners are away from home.

Some people play music for lonely dogs, but according to an Audible press release, a 2015 academic study revealed that audiobooks worked better than tunes to calm stressed-out pets. To investigate the phenomenon further, Audible teamed up with Cesar Millan, the dog behaviorist who’s better known as the "Dog Whisperer." Their own research—which they conducted with 100 dogs, in partnership with Millan’s Dog Psychology Center in Santa Clarita, California—found that 76 percent of participating dog owners noticed that audiobooks helped their pets chill out.

Dog owners can play Cesar Millan’s new Guide to Audiobooks for Dogs—which is both written and narrated by Millan—for initiation purposes, along with a curated rotating selection of dog-focused audiobook titles including Trevor Noah’s Born a Crime: Stories from a South African Childhood, performed by Trevor Noah; Jane Austen’s Pride and Prejudice, performed by Rosamund Pike; and W. Bruce Cameron’s A Dog’s Purpose, performed by William Dufris. Each title features a special video introduction by Millan, in which he explains why the book is suited for doggy ears. (Pro tip: According to Audible’s research, dogs prefer narrators of the same gender as their primary owners, and books played at normal volume on an in-home listening device.)

Don’t have an Audible subscription, but want to see if your dog succumbs to the purportedly calming magic of audiobooks? New listeners can listen to one free Audible for Dogs selection with a 30-day membership trial.

[h/t Fast Company]

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