2019年3月23日雅思阅读真题+题目+答案：Leaf-cutting ants and fungus

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2019年3月23日雅思阅读真题+题目+答案：Leaf-cutting ants and fungus切叶蚁和真菌

A )The ants and their agriculture have been extensively studied over the years, but the recent research has uncovered intriguing new findings about the fungus they cultivate, how they domesticated it and how they cultivate it and preserve it from pathogens. For example, the fungus farms, which the ants were thought to keep free of pathogens, turn out to be vulnerable to a devastating mold, found nowhere else but in ants’ nests. To keep the mold in check,the ants long ago made a discovery that would do credit to any pharmaceutical laboratory.

B )Leaf-cutting ants and their fungus farms are a marvel of nature and perhaps the best known example of symbiosis, the mutual dependence of two species. The ants’ achievement is remarkable — the biologist Edward O. Wilson has called it “one of the major breakthroughs in animal evolution” — because it allows them to eat, courtesy of their mushroom’s digestive powers, the otherwise poisoned harvest of tropical forests whose leaves are laden with terpenoids,alkaloids and other chemicals designed to sicken browsers.

C )Fungus growing seems to have originated only once in evolution, because all gardening ants belong to a single tribe, the descendants of the first fungus farmer. There are more than 200 known species of the attine ant tribe, divided into 12 groups, or genera. The leaf-cutters use fresh vegetation; the other groups, known as the lower attines because their nests are smaller and their techniques more primitive, feed their gardens with detritus like dead leaves, insects and feces. In 1994 a team of four biologists, Ulrich G. Mueller and Ted R. Schultz from Cornell University and Ignacio H. Chapela and Stephen A. Rehner from the United States Department of Agriculture, analyzed the DNA of ant funguses. The common assumption that the funguses are all derived from a single strain, they found, was only half true.

D )The leaf-cutters’ fungus was indeed descended from a single strain, propagated clonally, or just by budding, for at least 23 million years. But the lower attine ants used different varieties of the fungus, and in one case a quite separate species, the four biologists discovered.Cameron R. Currie, a Ph.D. student in the University of Toronto, it seemed to Mr. Currie,resembled the monocultures of various human crops, that are very productive for a while and then succumb to some disastrous pathogen, such as the Irish potato blight. Monocultures,which lack the genetic diversity to respond to changing environmental threats, are sitting ducks for parasites. Mr. Currie felt there had to be a parasite in the ant-fungus system. But a century of ant research offered no support for the idea. Textbooks describe how leaf-cutter ants scrupulously weed their gardens of all foreign organisms. “People kept telling me, ‘You know the ants keep their gardens free of parasites, don’t you?’” Mr. Currie said of his efforts to find a hidden interloper.

E )But after three years of sifting through attine ant gardens, Mr. Currie discovered they are far from free of infections. In last month’s issue of the Proceedings of the National Academy of Sciences, he and two colleagues, Dr. Mueller and David Mairoch, isolated several alien organisms, particularly a family of parasitic molds called Escovopsis.

F)Escovopsis turns out to be a highly virulent pathogen that can devastate a fungus garden in a couple of days. It blooms like a white cloud, with the garden dimly visible underneath. In a day or two the whole garden is enveloped.“Other ants won’t go near it and the ants associated with the garden just starve to death,’’Dr. Rehner said. “They just seem to give up, except for those that have rescued their larvae.”

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H )。。。。此处省略雅思阅读真题原文！

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雅思阅读真题题目如下：14-26题

Questions 14-19

Use the information in the passage to match the options (listed A-C) with the activities or features of ants below.

Write the appropriate letters, A-C, in boxes 14-19 on your answer sheet.

NB You may use any letter more than once.

A Leaf-cutting ants

B Lower attine ants

C Both leaf-cutting ants and lower attine ants

14 can use toxic leaves to feed fungus

15 build small nests and live with different foreign fungus

16 use dead vegetation to feed fungus

17 raise a single fungus which do not live with other variety of foreigners

18 normally keep a highly dangerous parasite under control

19 use special strategies to fight against Escovopsis

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