GRE阅读高频机经原文及答案:鸟叫研究-查字典英语网
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GRE阅读高频机经原文及答案:鸟叫研究

发布时间:2016-03-01  编辑:查字典英语网小编

  17. 鸟叫研究 新题

  Over the years, biologists have suggested two main pathways by which sexual selection may have shaped the evolution of male birdsong. In the first, male competition and intrasexual selection produce relatively short, simple songs used mainly in territorial behavior. In the second, female choice and intersexual selection produce longer, more complicated songs used mainly in mate attraction; like such visual ornamentation as the peacocks tail, elaborate vocal characteristics increase the males chances of being chosen as a mate, and he thus enjoys more reproductive success than his less ostentatious rivals. The two pathways are not mutually exclusive, and we can expect to find examples that reflect their interaction. Teasing them apart has been an important challenge to evolutionary biologists.

  Early research confirmed the role of intrasexual selection. In a variety of experiments in the field, males responded aggressively to recorded songs by exhibiting territorial behavior near the speakers. The breakthrough for research into intersexual selection came in the development of a new technique for investigating female response in the laboratory. When female cowbirds raised in isolation in sound-proof chambers were exposed to recordings of male song, they responded by exhibiting mating behavior. By quantifying the responses, researchers were able to determine what particular features of the song were most important. In further experiments on song sparrows, researchers found that when exposed to a single song type repeated several times or to a repertoire of different song types, females responded more to the latter. The beauty of the experimental design is that it effectively rules out confounding variables; acoustic isolation assures that the female can respond only to the song structure itself.

  If intersexual selection operates as theorized, males with more complicated songs should not only attract females more readily but should also enjoy greater reproductive success. At first, however, researchers doing fieldwork with song sparrows found no correlation between larger repertoires and early mating, which has been shown to be one indicator of reproductive success; further, common measures of male quality used to predict reproductive success, such as weight, size, age, and territory, also failed to correlate with song complexity.

  The confirmation researchers had been seeking was finally achieved in studies involving two varieties of warblers. Unlike the song sparrow, which repeats one of its several song types in bouts before switching to another, the warbler continuously composes much longer and more variable songs without repetition. For the first time, researchers found a significant correlation between repertoire size and early mating, and they discovered further that repertoire size had a more significant effect than any other measure of male quality on the number of young produced. The evidence suggests that warblers use their extremely elaborate songs primarily to attract females, clearly confirming the effect of intersexual selection on the evolution of birdsong.

  17.1. The passage is primarily concerned with

  showing that intrasexual selection has a greater effect on birdsong than does intersexual selection

  contrasting the role of song complexity in several species of birds

  describing research confirming the suspected relationship between intersexual selection and the complexity of birdsong

  demonstrating the superiority of laboratory work over field studies in evolutionary biology

  illustrating the effectiveness of a particular approach to experimental design in evolutionary biology

  17.2. The author mentions the peacocks tail in line 8 most probably in order to

  cite an exception to the theory of the relationship between intrasexual selection and male competition

  illustrate the importance of both of the pathways that shaped the evolution of birdsong

  draw a distinction between competing theories of intersexual selection

  give an example of a feature that may have evolved through intersexual selection by female choice

  refute a commonly held assumption about the role of song in mate attraction

  17.3. According to the passage, which of the following is specifically related to intrasexual selection?

  Female choice

  Territorial behavior

  Complex song types

  Large song repertoires

  Visual ornamentation

  17.4. Which of the following, if true, would most clearly demonstrate the interaction mentioned in lines 11-13?

  Female larks respond similarly both to short, simple songs and to longer, more complicated songs.

  Male canaries use visual ornamentation as well as elaborate song repertoires for mate attraction.

  Both male and female blackbirds develop elaborate visual and vocal characteristics.

  Male jays use songs to compete among themselves and to attract females.

  Male robins with elaborate visual ornamentation have as much reproductive success as rivals with elaborate vocal characteristics.

  17.5. The passage indicates that researchers raised female cowbirds in acoustic isolation in order to

  eliminate confounding variables

  approximate field conditions

  measure reproductive success

  quantify repertoire complexity

  prevent early mating

  17.6. According to the passage, the song sparrow is unlike the warbler in that the song sparrow

  uses songs mainly in territorial behavior

  continuously composes long and complex songs

  has a much larger song repertoire

  repeats one song type before switching to another

  responds aggressively to recorded songs

  17.7. The passage suggests that the song sparrow experiments mentioned in lines 37-43 failed to confirm the role of intersexual selection because

  females were allowed to respond only to the song structure

  song sparrows are unlike other species of birds

  the experiments provided no evidence that elaborate songs increased male reproductive success

  the experiments included the songs of only a small number of different song sparrows

  the experiments duplicated some of the limitations of previous field studies

  答案:CDBDADC

  

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