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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
Pigeons Are Secretly Brilliant Birds That Understand Space and Time, Study Finds
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Of all the birds in the world, the pigeon draws the most ire. Despite their reputation as brainless “rats with wings,” though, they’re actually pretty brilliant (and beautiful) animals. A new study adds more evidence that the family of birds known as pigeons are some of the smartest birds around, as Quartz alerts us.

In addition to being able to distinguish English vocabulary from nonsense words, spot cancer, and tell a Monet from a Picasso, pigeons can understand abstract concepts like space and time, according to the new study published in Current Biology. Their brains just do it in a slightly different way than humans’ do.

Researchers at the University of Iowa set up an experiment where they showed pigeons a computer screen featuring a static horizontal line. The birds were supposed to evaluate the length of the line (either 6 centimeters or 24 centimeters) or the amount of time they saw it (either 2 or 8 seconds). The birds perceived "the longer lines to have longer duration, and lines longer in duration to also be longer in length," according to a press release. This suggests that the concepts are processed in the same region of the brain—as they are in the brains of humans and other primates.

But that abstract thinking doesn’t occur in the same way in bird brains as it does in ours. In humans, perceiving space and time is linked to a region of the brain called the parietal cortex, which the pigeon brains lack entirely. So their brains have to have some other way of processing the concepts.

The study didn’t determine how, exactly, pigeons achieve this cognitive feat, but it’s clear that some other aspect of the central nervous system must be controlling it. That also opens up the possibility that other non-mammal animals can perceive space and time, too, expanding how we think of other animals’ cognitive capabilities.

[h/t Quartz]

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The Queen's Racing Pigeons Are in Danger, Due to an Increase in Peregrine Falcons
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Queen Elizabeth is famous for her love of corgis and horses, but her pet pigeons don't get as much press. The monarch owns nearly 200 racing pigeons, which she houses in a luxury loft at her country estate, Sandringham House, in Norfolk, England. But thanks to a recent boom in the region’s peregrine falcon population, the Queen’s swift birds may no longer be able to safely soar around the countryside, according to The Telegraph.

Once endangered, recent conservation efforts have boosted the peregrine falcon’s numbers. In certain parts of England, like Norfolk and the city of Salisbury in Wiltshire, the creatures can even find shelter inside boxes installed at local churches and cathedrals, which are designed to protect potential eggs.

There’s just one problem: Peregrine falcons are birds of prey, and local pigeon racers claim these nesting nooks are located along racing routes. Due to this unfortunate coincidence, some pigeons are failing to return to their owners.

Pigeon racing enthusiasts are upset, but Richard Salt of Salisbury Cathedral says it's simply a case of nature taking its course. "It's all just part of the natural process,” Salt told The Telegraph. "The peregrines came here on their own account—we didn't put a sign out saying 'room for peregrines to let.' Obviously we feel quite sorry for the pigeons, but the peregrines would be there anyway."

In the meantime, the Queen might want to keep a close eye on her birds (or hire someone who will), or consider taking advantage of Sandringham House's vast open spaces for a little indoor fly-time.

[h/t The Telegraph]

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