Gray wolves once were seen here and there in the Yellowstone area and much of the continental United States, but they were gradually displaced by human development. By the 1920s, wolves had practically disappeared from the Yellowstone area. They went farther north into the deep forests of Canada, where there were fewer humans around.

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What does the underlined word “displaced” in paragraph 2 mean?

Plastic-Eating Worms

Humans produce more than 300 million tons of plastic every year. Almost half of that winds up in landfills (垃圾填埋场), and up to 12 million tons pollute the oceans. So far there is no effective way to get rid of it, but a new study suggests an answer may lie in the stomachs of some hungry worms.

Researchers in Spain and England recently found that the worms of the greater wax moth can break down polyethylene, which accounts for 40% of plastics. The team left 100 wax worms on a commercial polyethylene shopping bag for 12 hours, and the worms consumed and broke down about 92 milligrams, or almost 3% of it. To confirm that the worms’ chewing alone was not responsible for the polyethylene breakdown, the researchers made some worms into paste (糊状物) and applied it to plastic films. 14 hours later the films had lost 13% of their mass — apparently broken down by enzymes (酶) from the worms’ stomachs. Their findings were published in Current Biology in 2017.

Federica Bertocchini, co-author of the study, says the worms’ ability to break down their everyday food — beeswax — also allows them to break down plastic. “Wax is a complex mixture, but the basic bond in polyethylene, the carbon-carbon bond, is there as well,” she explains, “The wax worm evolved a method or system to break this bond.”

Jennifer DeBruyn, a microbiologist at the University of Tennessee, who was not involved in the study, says it is not surprising that such worms can break down polyethylene. But compared with previous studies, she finds the speed of breaking down in this one exciting. The next step, DeBruyn says, will be to identify the cause of the breakdown. Is it an enzyme produced by the worm itself or by its gut microbes (肠道微生物)?

Bertocchini agrees and hopes her team’s findings might one day help employ the enzyme to break down plastics in landfills. But she expects using the chemical in some kind of industrial process — not simply “millions of worms thrown on top of the plastic.”

THE AMAZING ANIMALS OF AUSTRALIA

Our topic today is “Creatures Unique to Australia”, with questions answered by wildlife expert, Dr Jim Smith.

It has to be the kangaroo, as it has a wide distribution throughout the country. It’s a tough animal that has to survive in a difficult environment. Also, it cannot walk backwards, so it is always moving forwards. This expresses the strength and resolve of the Australians as individuals and as a nation. Baby kangaroos weigh only two grammes at birth. They then find their way into their mother’s pouch — a kind of pocket — to stay safe and warm. They sleep and drink milk in that temporary, protected environment until they are about seven or eight months old. After this phase, they go out to try their legs. After they learn to jump, they gradually spend less time with their mother and learn to be independent. Kangaroos may look cute, but encounters with them don’t always end so well. Kangaroos can hit and kick very hard, so please folks, if you see some kangaroos, remember they’re not for petting!

They are really quite cute, but the truth is, koalas are very sensitive creatures who can easily panic because of even small changes in their environment. They spend quite a lot of time eating, sleeping, and hanging onto tree trunks, so interaction with humans can cause them a lot of stress. Because of this, the government began to make laws against touching koalas, in the interest of animal protection, as well as public safety. So, if you see one in the wild, you shouldn’t approach it to pick it up or even touch it. If you want to hold a koala, you have to go to certain licensed zoos where animal experts make sure that the koalas selected for each session are in a good state for human contact and that they are handled for only a limited time and on a limited frequency of occasions.

My favourite is a little creature called the Tasmanian devil. If you are out camping in Tasmania and come across one, the experience might scare you! Tasmanian devils hunt at night, so you won’t usually see them, but you may hear their loud cries when they are fighting or eating. The noise they make could wake the dead. Frightening! They are about the size of small dogs and look like rather large black rats. They also have a terrible smell! Their diet is mostly dead animals. Fortunately, despite their name, they are generally not violent towards people.

Not at all. While it may lay eggs in a nest like a bird, it’s really a primitive mammal, with a unique biology. Its eggs hatch after about ten days, and then the baby platypus nurses from its mother like all other mammals. Its nose looks like a duck’s bill, and it has feet like a duck’s so it can dive under the water, but it’s covered in hair. Do you know what’s really strange about a platypus? The platypus doesn’t use its senses of sight or smell to find food. It has a capacity to find food in the water by using electrical sensors in its bill. There are only a small handful of animals in the world that can do that!