From Smells to Soundtracks

When a young sawfly, a bee-like insect, is threatened by its attackers like ants, it emits a mixture of unpleasant smells to defend itself. These emissions can seriously annoy a potential enemy.

Scientists wanting to study these smelly compounds—to understand which aspects of them discourage attackers and why—face great challenges. Meetups between sawflies and ants in a lab are difficult to carry out. There are also a very limited quantity of the insects’ emissions. On the side, Jean-Luc Boeve, a zoologist who studies insects, from the Royal Belgian Institute of Natural Sciences, is an amateur musician and composer. He decided to try a different way—the sound approach. “To be honest, I considered this project so unpractical myself that I set it aside,” he said. It was months before Boeve and his partner, Rudi Giot, finally made a resolution to get started on it.

They chose 16 sawfly species’ emissions to translate into sounds. First, they figured out which molecules(分子) were present in each smelly compound and in what amounts. Then they assigned various characteristics of those molecules matching properties of sound. For example, smaller molecules like a kind of acid found in vinegar, a sour-tasting liquid, evaporate(挥发) quickly, so Boeve and Giot assigned them sounds with higher pitch(音高). Larger molecules were given lower-pitched sounds. In all, the scientists created individual audio descriptions for 20 molecules. Then they combined the sound of each molecule present in a sawfly’s smell to construct the insect’s soundtrack. If a molecule was of higher proportion in an emission, they assigned it a higher volume. In such a case, the smaller a molecule is, the higher its pitch will be; and the higher the proportion of a molecule is, the higher its volume will be.

To test out the audio descriptions they created, Boeve and Giot examined people’s reactions to the soundtracks and compared them to ants’ reactions to the original smells. They played the 16 emission soundtracks and the 20 molecule sounds through speakers to about 50 study participants. Then the scientists measured how far people backed up to get to a “comfortable position” away from the noise. Most of the study volunteers told the researchers that the high pitch, as well as the high volume, was what made them withdraw. “Ants and volunteers moved away from a chemical and its matching soundtrack respectively,” the researchers wrote.

Boeve said he hoped the process would give other zoologists a new way to compare sawflies’ chemical defenses with those from other insects. It may also offer researchers clues about which molecules fight off enemies most.

Some people may be picky eaters, but as a species we are not. Birds, bugs and whales, we’ll eat them all. Yet our reliance on wild animals goes far beyond just feeding ourselves. From agricultural feed to medicine to the pet trade, modern society exploits wild animals in a way that beats even the most aggressive wild predator (捕食者). Now, for the first time, researchers have tried to capture the full picture of how we use wildlife, including how many, and for what purposes. The research showcases just how broad our influence on wild animals is.

In the study, researchers have found that humans kill, collect or otherwise use about 15,000 species. That’s up to 300 times more than the next top predator in any ecosystem.

Yet according to Chris Darimont, a co-author of the study, the biggest shock isn’t how many species we affect but why we take them. “The result,” he says, “is that we remove, or essentially prey on, more species of animals for non-food reasons than for food reasons.”And the biggest non-food use is as pets and pet food. “That’s where things have gone off the rails (轨道),” he says. The problem is especially serious for tropical birds. The helmeted hornbill, for example, is captured mainly for the pe trade, or for its beak to be used as medicine or to be carved like ivory. Their disappearance limits seed dispersal and the spread of trees around the forest.

Another big difference between humans’ influence on wild animals and that of other predators is that we tend to favor rare and exotic (外来的) species in a way other animals do not. Most predators target common species, since they are easier to find and catch. Humans, nowever, tend to covet the novel. “The more rare it is,” say scientists, “the more that drives up the price, and therefore it may go into extinction.”

If we want wild species to survive, we need to reestablish our relationship with them, perhaps from predator to caretaker.

In the far north, well above the Arctic Circle in Alaska, ground squirrels (地松鼠) are like little balls within a deep hole in the ground. If you look at one, you might think it is dead. The squirrel is as cold as ice. Its body temperature is –2℃. Its heart beats only once every 15 seconds. Its breathing stops for minutes at a time.

It’s not exanimate, of course — just hibernating (冬眠). But spring is on its way to Alaska. As the days are becoming longer and the ground becomes warm, the Arctic ground squirrels will be warm, too. At first, the increase will be almost too small to notice. “You see them begin to breathe a little more quickly — see their heart rate speed up,” says Brian Barnes, a zoologist of the University of Alaska. “As they get up to 10 to 20℃, you see them shivering (颤抖) quite clearly,” he notes, “just as we shiver.” This shivering is a type of way to create heat. “Once their body temperatures rise above 30℃,” he says, “they wake up, clean themselves, and move.” A squirrel that looked dead a few hours before is now very much alive.

Arctic ground squirrels are among the world’s coolest hibernators. Chilling out (放松) for months at a time lets them grow in this extremely cold place, where food is short. By studying how ground squirrels hibernate, scientists hope to answer some big questions. Among them: How do these animals go from warm to cold and back again? And might people ever do the same? The ability to chill out could help humans who suffer from brain injuries and heart problems survive.