SAT考试最新阅读真题（二）

　　SAT考试你都准备的怎么样了，关于阅读部分你有没有一些技巧，下面和小编一起来看看今年的SAT阅读考试真题吧。

　　Passage 3: Beans Talk, Natural Science

　　THE idea that plants have developed a subterranean internet, which they use to raise the alarm when danger threatens, sounds more like the science-fiction of James Cameron’s film “Avatar” than any sort of science fact. But fact it seems to be, if work by David Johnson of the University of Aberdeen is anything to go by. For Dr Johnson believes he has shown that just such an internet, with fungal hyphae standing in for local Wi-Fi, alerts beanstalks to danger if one of their neighbors is attacked by aphids.

　　Dr Johnson knew from his own past work that when broad-bean plants are attacked by aphids they respond with volatile chemicals that both irritate the parasites and attract aphid-hunting wasps. He did not know, though, whether the message could spread, tomato-like, from plant to plant. So he set out to find out—and to do so in a way which would show if fungi were the messengers.

　　As they report in Ecology Letters, he and his colleagues set up eight “mesocosms”, each containing five beanstalks. The plants were allowed to grow for four months, and during this time every plant could interact with symbiotic fungi in the soil.

　　Not all of the beanstalks, though, had the same relationship with the fungi. In each mesocosm, one plant was surrounded by a mesh penetrated by holes half a micron across. Gaps that size are too small for either roots or hyphae to penetrate, but they do permit the passage of water and dissolved chemicals. Two plants were surrounded with a 40-micron mesh. This can be penetrated by hyphae but not by roots. The two remaining plants, one of which was at the center of the array, were left to grow unimpeded.

　　Five weeks after the experiment began, all the plants were covered by bags that allowed carbon dioxide, oxygen and water vapor in and out, but stopped the passage of larger molecules, of the sort a beanstalk might use for signaling. Then, four days from the end, one of the 40-micron meshes in each mesocosm was rotated to sever any hyphae that had penetrated it, and the central plant was then infested with aphids.

　　At the end of the experiment Dr Johnson and his team collected the air inside the bags, extracted any volatile chemicals in it by absorbing them into a special porous polymer, and tested those chemicals on both aphids (using the winged, rather than the wingless morphs) and wasps. Each insect was placed for five minutes in an apparatus that had two chambers, one of which contained a sample of the volatiles and the other an odorless control.

　　The researchers found, as they expected from their previous work, that when the volatiles came from an infested plant, wasps spent an average of 3½ minutes in the chamber containing them and 1½ in the other chamber. Aphids, conversely, spent 1¾ minutes in the volatiles’ chamber and 3¼ in the control. In other words, the volatiles from an infested plant attract wasps and repel aphids.

　　Crucially, the team got the same result in the case of uninfected plants that had been in uninterrupted hyphae contact with the infested one, but had had root contact blocked. If both hyphae and roots had been blocked throughout the experiment, though, the volatiles from uninfected plants actually attracted aphids (they spent 3½ minutes in the volatiles’ chamber), while the wasps were indifferent. The same pertained for the odor of uninfected plants whose hyphae connections had been allowed to develop, and then severed by the rotation of the mesh.

　　Broad beans, then, really do seem to be using their fungal symbionts as a communications network, warning their neighbors to take evasive action. Such a general response no doubt helps the plant first attacked by attracting yet more wasps to the area, and it helps the fungal messengers by preserving their leguminous hosts.

　　Passage 4: Social Science (2), against Banks Labor Policy.

　　to be added.

　　Passage 5: Gouldian finches’ head colour reflects their personality, Natural Science

　　What this suggests is that behavioural characteristics, such as aggression and other traits, may be correlated with particular head colour morphs meaning that head colour is indicative of different personality types. This idea has been tested in a new paper by Leah Williams and her colleagues.

　　In order to determine if head colour really does indicate personality traits in Gouldian finches Williams and her colleagues tested a number of predictions. First they looked at pairs of black-headed birds which were expected to show less aggression towards each other than pairs of red-headed birds, this makes sense since red-headed birds had previously been found to exhibit higher levels of aggression.

　　The second prediction was that red-headed birds should be bolder, more explorative and take more risks than black-headed birds. This hypothesis is based on previous studies of other species that have shown a correlation between aggression and these behavioural characteristics. However, there is another possibility, red-headed birds could take fewer risks for two reasons; first, they may be more conspicuous to predators due to their bright colouration and second, it may pay black headed birds to take more risks and be more explorative so they find food resources before the dominant red-headed birds do.

　　In order to test the first prediction paired birds of matching head colour were moved into an experimental cage without food. After one hour of food deprivation a feeder was placed into the corner of the cage where there was only enough room for one bird to feed at a time. aggressive interactions such as threat displays and displacements were then counted over a 30 minute period.

　　The results as shown in the figure below were striking. Red-headed birds were significantly and consistently more aggressive than black-headed birds.

　　To test the birds willingness to take risks they were deprived of food for one hour before their feeder was replaced. After the birds had calmly begun to feed a silhouette of an avian predator was moved up and down in front of the cage to scare the birds from the feeder. The time it took for them to return to the feeder was taken as a measure of their willingness to take risks, birds that returned quickly were considered to be greater risk takers than those that were more cautious.

　　This time the results were surprising. Red-headed birds were considerably more cautious than those with black heads at returning to the feeder after a “predator” had been introduced. As the figure below shows they took on average 4x longer to begin feeding again than the less aggressive black-headed birds.

　　Finally, the authors investigated the birds interest in novel objects or “object neophilia” which is defined in the paper as “exploration in which investigation is elicited by an object’s novelty“. To do this a bunch of threads was placed on a perch within the cage, the time taken for the birds to approach the threads within one body length and to touch them were recorded over a one hour period. In line with the results from the risk taking experiment it was found that the aggressive red-headed birds showed less interest in novel objects than did black-headed birds. The difference is not so striking as the previous experiments but was statistically significant nonetheless.

　　These experiments were repeated after a two month interval and showed that different birds differed in their responses but the responses of individual birds were consistent over time. Head colour was found to predict the behavioural responses of the birds. Red-headed birds were more aggressive than black-headed birds but took fewer risks and were not explorative.

　　What is surprising about these results is that aggression does not correlate with risk taking behaviour, however, the authors do provide a convincing explanation, suggesting that…

　　Interestingly boldness and risk taking behaviours were found to be strongly correlated, regardless of head colour they always occurred together forming a “behavioural syndrome”. This implies that there is selection in favour of specific combinations of traits and of head colour in relation to those traits. Selection favours aggression in red-headed birds and the boldness/risk taking behavioural syndrome in black-headed birds. This makes sense when you consider the high risk of predation faced by red-headed birds if they take too many risks and the need for black-headed birds to find food away from the dominant red heads which occupy the safest foraging locations.

　　Williams and her colleagues suggest that if red-headed birds are aggressive, and black-headed birds take more risks, this could lead to differences in foraging tactics. For example, black headed birds could increase their foraging opportunities by feeding at more risky sites away from interference by the dominant red-headed birds which feed in safer locations. The lower conspicuousness of their black heads means they are at less risk of predation at exposed sites that red-headed birds would be.

　　The results of this fascinating study strongly support the hypothesis that head colour does indeed signal personality in Gouldian finches. I would love to see some more research in this area. The authors themselves suggest that more research is needed to find out what roles head colours play in social situations. It would also be interesting to find out how widespread this phenomenon is, given that birds frequently use plumage colouration as signals it seems likely to me that colour may indicate personality in other avian species.

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