GRE阅读高频机经原文及答案：鸟叫研究

　　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