Leaf-CuttingAnts and Fungus 切叶蚁和真菌
A ）The ants and their agriculture have been extensivelystudied over the years, but the recent research has uncovered intriguing newfindings about the fungus they cultivate, how they domesticated it and how theycultivate it and preserve it from pathogens. For example, the fungus farms,which the ants were thought to keep free of pathogens, turn out to bevulnerable to a devastating mold, found nowhere else but in ants’ nests. Tokeep the mold in check,the ants long ago made a discovery that would do creditto any pharmaceutical laboratory.
B ）Leaf-cutting ants and their fungus farms are a marvelof nature and perhaps the best known example of symbiosis, the mutualdependence of two species. The ants’ achievement is remarkable — the biologistEdward O. Wilson has called it “one of the major breakthroughs in animalevolution” — because it allows them to eat, courtesy of their mushroom’sdigestive powers, the otherwise poisoned harvest of tropical forests whoseleaves are laden with terpenoids,alkaloids and other chemicals designed tosicken browsers.
C ）Fungus growing seems to have originated only once inevolution, because all gardening ants belong to a single tribe, the descendantsof the first fungus farmer. There are more than 200 known species of the attineant tribe, divided into 12 groups, or genera. The leaf-cutters use freshvegetation; the other groups, known as the lower attines because their nestsare smaller and their techniques more primitive, feed their gardens with detrituslike dead leaves, insects and feces. In 1994 a team of four biologists, UlrichG. Mueller and Ted R. Schultz from Cornell University and Ignacio H. Chapelaand Stephen A. Rehner from the United States Department of Agriculture,analyzed the DNA of ant funguses. The common assumption that the funguses areall derived from a single strain, they found, was only half true.
D ）The leaf-cutters’ fungus was indeed descended from asingle strain, propagated clonally, or just by budding, for at least 23 millionyears. But the lower attine ants used different varieties of the fungus, and inone 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 veryproductive for a while and then succumb to some disastrous pathogen, such asthe Irish potato blight. Monocultures,which lack the genetic diversity torespond 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 centuryof ant research offered no support for the idea. Textbooks describe howleaf-cutter ants scrupulously weed their gardens of all foreign organisms.“People kept telling me, ‘You know the ants keep their gardens free ofparasites, don’t you?’” Mr. Currie said of his efforts to find a hiddeninterloper.
E ）But after three years of sifting through attine antgardens, Mr. Currie discovered they are far from free of infections. In lastmonth’s issue of the Proceedings of the National Academy of Sciences, he andtwo colleagues, Dr. Mueller and David Mairoch, isolated several alienorganisms, particularly a family of parasitic molds called Escovopsis.Escovopsis turns out to be a highly virulent pathogen that can devastate afungus garden in a couple of days. It blooms like a white cloud, with thegarden dimly visible underneath. In a day or two the whole garden isenveloped.“Other ants won’t go near it and the ants associated with the gardenjust starve to death,’’Dr. Rehner said. “They just seem to give up, except forthose that have rescued their larvae.”
F ）Evidently the ants usually manage to keep Escovopsisand other parasites under control. But with any lapse in control, or if theants are removed, Escovopsis will quickly burst forth.Although new leaf-cuttergardens start off free of Escovopsis, within two years some 60 percent becomeinfected. The discovery of Escovopsis’s role brings a new level of understandingto the evolution of the attine ants. “In the last decade, evolutionarybiologists have been increasingly aware of the role of parasites as drivingforces in evolution,” Dr. Schultz said. There is now a possible reason toexplain why the lower attine species keep changing the variety of fungus intheir mushroom gardens, and occasionally domesticating new ones — to stay onestep ahead of the relentless Escovopsis.
G ）Interestingly, Mr. Currie found that the leaf-cuttershad in general fewer alien molds in their gardens than the lower attines, yetthey had more Escovopsis infections. It seems that the price they pay forcultivating a pure variety of fungus is a higher risk from Escovopsis. But theleaf-cutters may have little alternative: they cultivate a special variety offungus which, unlike those grown by the lower attines, produces nutritiousswollen tips for the ants to eat.
H ）Discovery of a third partner in the ant-fungussymbiosis raises the question of how the attine ants, especially the leaf-cutters,keep this dangerous interloper under control. Amazingly enough, Mr. Currie hasagain provided the answer. “People have known for a hundred years that antshave a whitish growth on the cuticle,” said Dr. Mueller, referring to theinsects’ body surface. “People would say this is like a cuticular wax. ButCameron was the first one in a hundred years to put these things under amicroscope. He saw it was not inert wax. It is alive.” Mr. Currie discovered aspecialised patch on the ants’ cuticle that harbors a particular kind ofbacterium, one well known to the pharmaceutical industry, because it is thesource of half the antibiotics used in medicine. From each of 22 species ofattine ant studied, Mr.Cameron and colleagues isolated a species of Streptomycesbacterium, they reported in Nature in April. The Streptomyces does not havemuch effect on ordinary laboratory funguses. But it is a potent poisoner ofEscovopsis, inhibiting its growth and suppressing spore formation.Because boththe leaf-cutters and the lower attines use Streptomyces, the bacterium may havebeen part of their symbiosis for almost as long as the Escovopsis mold. If so,some Alexander Fleming of an ant discovered antibiotics millions of yearsbefore people did. Even now, the ants are accomplishing two feats beyond thepowers of human technology. The leaf-cutters are growing a monocultural cropyear after year without disaster, and they are using an antibiotic apparentlyso wisely and prudently that, unlike people, they are not provoking antibioticresistance in the target pathogen.
Questions 14-19
Use theinformation in the passage to match the options (listed A-C) with theactivities or features of ants below.
Write theappropriate letters, A-C, in boxes 14-19 on your answer sheet.
NB You may use anyletter more than once.
A Leaf-cuttingants
B Lower attineants
C Bothleaf-cutting ants and lower attine ants
14 can use toxicleaves to feed fungus
15 build smallnests and live with different foreign fungus
16 use deadvegetation to feed fungus
17 raise a singlefungus which do not live with other variety of foreigners
18 normally keep ahighly dangerous parasite under control
19 use specialstrategies to fight against Escovopsis
Questions 20-24
Reading Passage 2has eight paragraphs, A-H.
Which paragraphcontains the following information?
Write the correctletter, A-H, in boxes 20-24 on your answer sheet.
20 Dangerousoutcome of Escovopsis
21 Risk of growingsingle fungus
22 Comparison ofthe features of two different nests for feeding gardens
23 Discovery ofsignificant achievements made by ants earlier than human
24 Advantages ofgrowing a new breed of fungus in the ant farm
Questions 25-26
Choose the correctletter, A, B, C or D.
Write your answersin boxes 25-26 on your answer sheet.
25 What does theauthor think of Currie’s opinion on the saying “ants keep their gardens free ofparasites”?
A His viewpointwas verified later.
B His earlierstudy has sufficient evidence immediately.
C There is nodetail mentioned in the article.
D His opinion wasproved to be wrong later on.
26 What didscientists find on the skin of ants under microscope?
A some white cloudmold embed in their skin
B that wax is allover their skin
C a substancewhich is useful to humans
D a substancewhich suppresses growth of all fungus
题目详解
Questions14-19
14. 利用题目细节信息“ toxic leaves” 和“ feed fungus” 定位于原文段落 B 末句“ because it allows them to eat, courtesy oftheir mushroom’s digestive powers, the otherwise poi-soned harvest of tropicalforests whose leaves are laden with terpenoids, alkaloids and other chemicals designed to sickenbrowsers”。 这道题的难点在于找到题目中“ feed fungus”所 对 应 的 原 文。 文 中 说 到“ the otherwise poisoned harvest oftropical forests whose leaves are laden with terpenoids, alkaloids and other chemicalsdesigned to sicken browsers”， 既然热带雨林中的叶子有毒， 切叶蚁为什么还要收集而且不会中毒呢? 那是因为真菌的消化作用(mushroom’sdigestive powers) 。 此外， 文章 C 段还提到“ The leaf-cutters use fresh vegetation(切叶蚁使用新鲜的植被养活自己的真菌园) ”， 所以切叶蚁收集有毒的树叶是为了饲养真菌。因此， 正确答案为 A。
15. 利用题目细节信息“ small nests”、“ different” 和“ foreign” 定位于原文 C 段第 3 句与 D 段第 2 句。 C 段第 3 句“ the othergroups, known as the lower attines because their
nests are smaller and their techniques moreprimitive”， 这里讲的是“ 它们的巢较小且种植技术更原始，被称为 lower attines”。 原文中的 “ nests are smaller”对应题目中的 “ small nests”。 但本段未出现题目中的后半部分信息，需要接着往下看。 D 段第 2 句“ But the lower attine ants used different varieties of the fungus”， 这里说“ lower attine 蚂蚁使用不同种类的真菌”。 原文中的 “ different varieties of the fungus”对应题目中的 “ different foreign fungus”。结合原文内容， 此处讲的都是 lower attines， 因此正确答案为 B。
16. 利用题目细节信息“ dead vegetation” 定位于原文 C 段第 3 句“ known as the lower attines because their nests are smaller and their techniques moreprimitive, feed their gardens with detritus like dead leaves, insects and feces”。 这句话讲到“ 它们用枯叶、昆虫和粪便的碎屑来养活自己的园子”。 原文中的“ dead leaves” 与题目中的“ dead vegetation” 为同义替换， 所对应的是 lower attines。 因此， 正确答案为 B。
17. 利用题目细节信息“ a single fungus” 定位于 D 段首句“ The leaf-cutters’ fungus was indeed descended from a single strain, propagated clonally, or justby budding, for at least 23 million years.” 这里说“ 切叶蚁所种的菌种是单一菌株”， 而不像 lower attine ants那样 used different varieties of the fungus。 因此， 正确答案为 A。
18. 利 用 顺 序 原 则 定 位 于 原 文 E 段第 3 句“ Escovopsis turns out to be a highly virulent pathogen...” 和 F 段首 句“ Evidently the ants usually manage to keep Escovopsis and other parasites under control.” 这说明蚂蚁通常能够控制住 Escovopsis 这种高危险的寄生物， 这与题目相对应。 此外， H 段首句提到“ Discovery of a third partner in the antfungus symbiosis raises thequestion of how the attine ants, especially the leaf-cutters, keep this dangerous interloper under control.”这说明“ 果蚁， 尤其是切叶蚁能有效控制这种寄生物”， 对应 leaf-cutters。 因此， 正确答案为 A。
19. 利 用 顺 序 原 则 先 定 位 于 原 文 F 段， 该段 后 半 部 分 提 到“ lower attine species keep changing the variety of fungus intheir mushroom gardens, and occasionally domesticating new ones — to stay one step aheadof the relentless Escovopsis”。 这说明低等果蚁不断改变蘑菇园中的真菌品种， 偶尔还培育新的真菌品种，目的是为了在和无情的 Escovopsis 霉菌的对抗中占据上风。 然后再定位到原文 H 段首句“ Discoveryof a third partner inthe ant-fungus symbiosis raises the question of how the attine ants, especiallythe leaf-cutters,keep this dangerous interloper under control.” 这说明切叶蚁也能够通过“ 第三方” 来对抗 Escovopsis 霉菌。 因此， 这两种类型的蚂蚁都有自己的“ special strategies” 可以“ fight against Escovopsis”， 与题目相对应， 故正确答案为 C。
Questions20-24
20. 该信息出现在原文 E 段第 3 句“ Escovopsis turns out to be a highly virulent pathogen that can devastate a fungus gardenin a couple of days.” 这里讲到“ Escovopsis 霉菌是剧毒性病原体，它可以在几天之内毁灭一个真菌园”。 原文中的“ turns out to be” 表示“ 结
果”， 对应题目中的“ outcome”， 文中“ devastate a fungus garden in acouple of days”与题目中的“Dangerous outcome of Escovopsis” 相对应。 因此， 正确答案为 E。
21. 该信息出现在原文 D 段第 5 句话“ Monocultures, which lack the genetic diversity to respond to changing environmentalthreats, are sitting ducks for parasites.” 这里讲到“ 单一栽培往往因为缺乏基因的多样性来应对不断变化的环境威胁， 从而容易成为寄生虫攻击的目标”， 对应题目中的“ Risk of growing single fungus(单一种植的风险)”。
因此， 正确答案为 D。
22. 该信息出现在原文 C 段第 3 句“ The leaf-cutters use fresh vegetation; the other groups,known asthe lower attines because their nests are smaller and their techniques moreprimitive, feed their gardens with detritus like dead leaves, insects andfeces.” 这里提及“leafcutters” 使用新鲜的植被养活自己的园子， 而后面紧接着对比说到“ lower attines” 由于巢穴较小， 技术也更加原始， 因此使用枯叶、 昆虫和粪便等碎屑来养活自己的园子，前后两者对比，正好与题目相对应。 因此， 正确答案为 C。
23. 该信息出现在原文 H 段倒数第 2、 3 句“ If so, someAlexander Fleming of an ant discovered antibiotics millions of years beforepeople did. Even now, the ants are accomplishing two feats beyond the powers ofhuman technology.” 原文讲到蚂蚁先于人类发现抗生素，并且即使到现在， 蚂蚁仍然有两项成果超越人类。原文中的“ two feats” 与题目中的 “ two achievements”为同义替换，而 “ millions of years beforepeople did”和 “ beyond the powers of human technology” 与题目中的“ earlier than human” 相对应。 因此， 正确答案为 H。
24. 该信息出现在原文 F 段末句“ ...and occasionallydomesticating new ones — to stay one step ahead of the relentless Escovopsis”。 这里提到“ 培育新的真菌品种是为了在和无情的 Escovopsis 霉菌的对抗中占据上风”。 原文中的“ domesticating new ones” 与题目中的“ growing a new breed of fungus” 为同义替换，其中“ ones” 指代的是原文前面提到的“ fungus”。 因此， 正确答案为 F。
Questions25-26
解 答
25. 该信息出现在原文 D 段与 E 段，首先， 看到 D 段“ Mr. Curriefelt there had to be a parasite in the ant-fungus system. But a century of ant researchoffered no support for the idea.” 这里提到“ 柯里先生认为在蚂蚁与真菌的体系中一定有寄生虫存在。 但是这个想法在过去一个世纪对蚂蚁的研究中并未得到任何证据支持”。 但 E 段接着写道 “ Inlast month’s issue of the Proceedings of the National Academy of Sciences, heand two colleagues, Dr. Mueller and David Mairoch, isolated several alienorganisms, particularly a family of parasitic molds called Escovopsis.” 这里说的是“ 柯里先生与他的同事分离出了几个外来生物的菌种， 特别是一种叫作 Escovopsis 的寄生霉菌族”。 这就说明Currie 之前的猜想得到了证实， 选项 A(他的观点后来得到了证实) 符合原文内容。
因此， 正确答案为 A。
26. 利用题目细节信息“ under microscope” 定位于原文 H 段“ People would say this is like a cuticular wax. But Cameronwas the first one in a hundred years to put these things under a microscope. He saw it wasnot inert wax. It is alive.” 这里提到“ 卡梅隆把这些东西放在显微镜下观察，发现蚂蚁表皮上的不是惰性蜡，而是活性的”。 紧接又提到“ Mr.Currie discovered a specialised patch on the ants’ cuticle thatharbours a particular kind of bacterium, one well known to the pharmaceutical industry, because itis the source of half the antibiotics used in medicine.” 这说明“ 蚂蚁的表皮有一种特殊的斑点， 其中隐藏着一种特殊的细菌。 这种细菌对于制药行业来说是非常有名的，因为医学上使用的抗生素多半来源于此”。 选项 A“ 一些白色的云状霉菌嵌在它们的表皮上”， 但原文中并没有说是“ white cloud mold”，因此排除选项 A。 选项 B“ 蜡遍布在它们的皮肤上”，但原文中仅仅说的是“ He saw it was not inertwax. It is alive.(表皮上的不是惰性蜡，而是活性的。)” 因此排除 B 选项。 D 选项“ 一种能够抑制所有真菌生长的物质” 在文中没有提及，因此排除 D选项。 选项 C“ 一种对人类有用的物质”，题目中的“ useful to humans” 与原文中的“ one well known to thepharmaceutical industry” 相对应。 因此，正确答案为 C。
答案：
14.A 15.B 16.B 17.A 18.A 19.C 20.E
21.D 22.C 23.H 24.F 25.A 26.C
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