2015年英语四级考试听力短文

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2015年英语四级考试听力短文

　　Many science fiction stories tell about explorers arriving in a new world. The explorers then use some kind of high-tech device to test for breathable air or signs of life. But here on Earth, science fiction is becoming reality through a new sampling technology called environmental DNA, or eDNA for short. Scientists can use it to identify rare or invasive species, study biodiversity or estimate fish populations with just a little air or water.

2015年英语四级考试听力短文

　　Ryan Kelly is an ecologist at the School of Marine and Environmental Affairs at the University of Washington in Seattle. He works in a laboratory there with other researchers. They study the genetic material released by living creatures.

　　"Essentially we can take a sample of soil or air -- and in our case -- water, and we can sequence the DNA out of it and tell you what is there."

　　Ryan Kelly says he and his research team are studying water samples collected from Puget Sound. He says the cost of gene sequencing has "plummeted in recent years." That makes DNA testing more widely available.

　　Researcher Jimmy O'Donnell at the University of Washington lab, where he processes eDNA samples. (T. Banse/VOA)

　　Environmental DNA can be used in two ways. One is to identify the creatures that live in a certain place. The other is to confirm the presence or lack of a specific creature.

　　Caren Goldberg heads the new eDNA lab at Washington State University in Pullman, Washington. She is one of the first biologists in the northwestern United States to take the technology from the testing phase to actually using it.

　　"It is extremely useful for species that are really hard to find. I have spent many hours looking for species that I was pretty sure were there -- looking under rocks, looking in water, doing all kinds of surveys."

　　Caren Goldberg sees eDNA as a way to get answers more efficiently, safely and with less destruction compared to traditional survey techniques. Until recently, scientists depended on snorkeling, netting or using an electric current to temporarily capture fish.

　　"We're absolutely at this point where proof-of-concept has been established. I don't think everyone necessarily is on board yet, but I think the majority of the people are on board."

　　This newer way to identify what lives in the environment is becoming popular around the world. Animal experts in Vietnam are using the eDNA to find the last, wild Yangtze giant softshell turtles. One researcher on the Caribbean island of Trinidad is using the sampling technology to find endangered golden treefrogs. And in Madagascar, it is being used to identify amphibian diseases.

　　Ms. Goldberg has used eDNA testing to confirm the local extinction, disappearance, of a leopard frog in the American state of Idaho. She has also been asked to document the spread of the New Zealand mudsnail in the state of Washington. The creature has been found in lakes and other waterways across the state.

　　Now, the U.S. Bureau of Land Management wants Caren Goldberg to look for the Columbia spotted frog in two other western states. The rare amphibian is a candidate for the federal government's threatened species list.

　　Scientists working with the technology say they do not expect robots to replace field biologists anytime soon. But the old-fashioned field work could soon be more targeted.

　　A related research goal is to show how long environmental DNA can last and how far it can travel in different environments.

　　And that’s the Environment and Science Report from VOA Learning English. For more environment, science and agriculture reports, go to our website 51voa.com. I’m Jonathan Evans.

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