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  Vocalization in Frogs

  The Túngara frog is a small terrestrial vertebrate that is found in Central America. Túngara frogs breed in small pools, and breeding groups range from a single male to choruses of several hundred males. The advertisement call of a male Túngara frog is a strange noise, a whine that starts at a frequency of 900 hertz and sweeps downward to 400 hertz in about 400 milliseconds. The whine may be produced by itself, or it may be followed by one or several chucks or clucking sounds. When a male Túngara frog is calling alone in a pond, it usually gives only the whine portion of the call, but as additional males join a chorus, more and more of the frogs produce calls that include chucks. Scientists noted that male Túngara frogs calling in a breeding pond added chucks to their calls when they heard the recorded calls of other males played back. That observation suggested that it was the presence of other calling males that incited frogs to make their calls more complex by adding chucks to the end of the whine.

  What advantage would a male frog in a chorus gain from using a whine-chuck call instead of a whine?

  Perhaps the complex call is more attractive to female frogs than the simple call. Michael Ryan and Stanley Rand tested that hypothesis by placing female Túngara frogs in a test arena with a speaker at each side. One speaker broadcast a pre-recorded whine call, and the second speaker broadcast a whine-chuck. When female frogs were released individually in the center of the arena, fourteen of the fifteen frogs tested moved toward the speaker broadcasting the whine-chuck call.

  If female frogs are attracted to whine-chuck calls in preference to whine calls, why do male frogs give whine-chuck calls only when other males are present? Why not always give the most attractive call possible? One possibility is that whine-chuck calls require more energy than whines, and males save energy by only using whine-chucks when competition with other males makes the energy expenditure necessary. However, measurements of the energy expenditure of calling male Túngara frogs showed that energy cost was not related to the number of chucks. Another possibility is that male frogs giving whine- chuck calls are more vulnerable to predators than frogs giving only whine calls. Túngara frogs in breeding choruses are preyed upon by a species of frog-eating bats, Trachops cirrhosus, and it was demonstrated that the bats locate the frogs by homing on their vocalizations.

  In a series of playback experiments, Michael Ryan and Merlin Tuttle placed pairs of speakers in the forest and broadcast vocalizations of Túngara frogs. One speaker played a recording of a whine and the other a recording of a whine-chuck. The bats responded as if the speakers were frogs: they flew toward the speakers and even landed on them. In five experiments at different sites, the bats approached speakers broadcasting whine-chuck calls twice as frequently as those playing simple whines (168 approaches versus 81). Thus, female frogs are not alone in finding whine-chuck calls more attractive than simple whines. An important predator of frogs also responds more strongly to the complex calls.

  Ryan and his colleagues measured the rates of predation in Túngara frog choruses of different sizes. Large choruses of frogs did not attract more bats than small choruses, and consequently the risk of predation for an individual frog was less in a large chorus than in a small one. ■ Predation was an astonishing 19 percent of the frogs per night in the smallest chorus and a substantial 1.5 percent per night even in the largest chorus. ■ When a male frog shifts from a simple whine to a whine-chuck call, it increases its chances of attracting a female, but it simultaneously increases its risk of attracting a predator. In small choruses, the competition from other males for females is relatively small, and the risk of predation is relatively large.

  Under these conditions it is apparently advantageous for a male Túngara frog to give simple whines. However, as chorus size increases, competition with other males also increases while the risk of predation falls. In that situation, the advantage of giving a complex call apparently outweighs the risks. ■

  1. The word “incited” in the passage is closest in meaning to

  A. allowed

  B. stimulated

  C. forced

  D. helped

  2. According to paragraph 1, male Túngara frogs add chucks to the whine they produce when

  A. potential mates are unable to hear the frequency of their whine sounds

  B. other males produce louder whine sounds than they do

  C. the frogs breed in large pools rather than small ones

  D. other males are present in their breeding pool

  3. What is the relationship of paragraph 2 in the passage to paragraph 1

  A. Paragraph 2 provides additional support for a scientific hypothesis discussed in paragraph 1.

  B. Paragraph 2 questions the accuracy of a scientific observation discussed in paragraph 1.

  C. Paragraph 2 provides a possible explanation for a scientific observation discussed in paragraph 1.

  D. Paragraph 2 identifies some strengths and weaknesses of a scientific hypothesis discussed in paragraph 1.

  4. According to paragraph 2, Ryan and Rand conducted an experiment to find out whether which of the following theories was true

  A. Male frogs in a chorus use a whine-chuck call in place of a whine call.

  B. Female frogs prefer a whine-chuck call to a simple whine call.

  C. Male frogs tend to produce more whine-chuck calls than whine calls.

  D. Female frogs respond differently to live calls from males than they do to recorded calls.

  5. To be attracted to whine-chuck calls in preference to whine calls means

  A. to like whine-chuck calls instead of whine calls

  B. to like whine-chuck calls in addition to whine calls

  C. to like whine-chuck calls followed by whine calls

  D. to like whine-chuck calls more than whine calls

  6. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage. Incorrect choices change the meaning in important ways or leave out essential information.

  A. Males may save energy when competing for mates by using only whine-chuck calls rather than both

  whines and whine-chucks.

  B. Males expend as much of their energy on whine-chuck calls as on whine calls when competing with other males.

  C. Males save energy by using whine-chuck calls only when competing with other males.

  D. Males that save energy by using only whines are less able to compete with other males.

  7. According to paragraph 4, all of the following are true of the playback experiments EXCEPT:

  A. Female frogs and predator bats approached the broadcasting speakers.

  B. The bats responded more strongly to the whine-chuck calls than they responded to the whine calls.

  C. Each speaker played a different kind of male frog call.

  D. The same experiment was repeated at different locations.

  8. According to paragraph 4, the playback experiments of Ryan and Tuttle demonstrated which of the following

  A. Túngara frogs use both whines and whine-chucks in their vocalizations.

  B. Female Túngara frogs are attracted to both whine and whine-chuck vocalizations.

  C. Female Túngara frogs and predators of t¨²ngara frogs are attracted to different types of vocalizations.

  D. Frog-eating bats are attracted to whine-chuck calls more than to whines alone.

  9. The word “substantial” in the passage is closest in meaning to

  A. average

  B. smaller

  C. considerable

  D. surprising

  10. The word “outweighs” in the passage is closest in meaning to

  A. exceeds

  B. ignores

  C. minimizes

  D. disguises

  11. According to paragraph 5, all of the following are true about Túngara frog vocalizations EXCEPT:

  A. The larger the frog chorus, the smaller the chance there is of a particular frog being eaten by a predatory bat.

  B. The larger the frog chorus, the louder each individual frog calls.

  C. The smaller the frog chorus, the easier it is for a frog to attract a female.

  D. The smaller the frog chorus, the more likely it becomes that a frog using the whine-chuck vocalization will be attacked by a bat.

  12. Which of the following can be inferred from paragraph 5 about the behavior of male Túngara frogs

  A. When in small choruses they use less effective mating calls to decrease their risk of predation.

  B. They avoid joining a large chorus in a breeding pool because it increases the risk of predation.

  C. They avoid the use of the whine-chuck call whenever there is the risk of predators.

  D. They attempt to avoid predation by making their calls at night.

  13. Look at the four squares that indicate where the following sentence could be added to the passage.

  Predation, therefore, is a risk in choruses of all sizes, but the risk varies depending on the type of call used.

  Where would the sentence best fit? Click on a square to add the sentence to the passage.

  14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

  Answer Choices

  A. Túngara frogs generally use simple calls when they wish to attract a mate, and complex calls when they wish to avoid predation.

  B. Two hypotheses have been put forward about why females and frog-eating bats are more attracted to males using whine-chuck calls.

  C. The hypothesis that whine calls are used to save energy when males are not in immediate competition with each other has been disproved by showing that chuck calls do not require more energy.

  D. Túngara females overwhelmingly favor the whine-chuck call used by the males, but so do certain bats that prey upon Túngara frogs.

  E. Most males gather in groups of several hundreds when calling because the rate of predation from bats is so high in small groups.

  F. Male Túngara frogs use the whine-chuck call in large groups, where their risk of predation is lower, and the whine call in small groups, where their risk is higher.

  参考答案

  Q1B Q2D Q3C Q4B Q5D Q6C Q7B Q8D Q9C Q10A

  Q11B Q12A Q13B Q14 CDF

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