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  3. Spiders are known for many things. Sociability is not one of them. Most spiders are more likely to try to eat their neighbours t

Spiders are known for many things. Sociability is not one of them. Most spiders are more likely to try to eat their neighbours t

admin2017-03-01  59
问题     Spiders are known for many things. Sociability is not one of them. Most spiders are more likely to try to eat their neighbours than befriend them. Given that there are at least 43,678 species of spiders, though, it is not too surprising that a few have overcome their natural bad-temper and teamed up to form societies. So far, about two dozen such social spiders have been identified. And among them, something really strange has just been found. For one type of spider society turns out to involve two different but closely related species. It is as though anthropologists (人类学家)had discovered villages populated both by human beings and chimpanzees.
    This was discovered by a team led by Lena Grinsted of Aarhus University in Denmark. They were studying a social species of spider called Chikunia nigra, living near Beratan Lake in Bali. Later, as they looked in more detail at their samples, they realised its genes showed that it was actually two species.
    It is not clear why the spiders are social. They do not hunt together. One explanation may be that the colony is acting like a huge kindergarten.
    Ms. Grinsted discovered this possibility by experiment. First, she identified 19 females who were looking after those who were recently born, and another 20 who had eggs. In each case she introduced a new comer, in the form of a spider from the same colony. Both mothers and mothers-to-be were surprisingly tolerant of what would, in most spider species, be a serious threat. Only 40% of the time did they attempt to chase the intruder away, or bite it.
    Ms. Grinsted then took another 40 spiders and replaced some of their little spiders. The result, she found, was that a female was as likely to look after and protect another’s young spider as she was her own.
    Which is interesting, but not all that extraordinary in social groups which are composed of closely related individuals. Except that Ms. Grinsted now knows that this cannot always be the case for her spiders, since two different species are involved. The species in question are pretty similar, which would seem to exclude another common cause of co-action; different spiders do different work in the group.
    Because Ms. Grinsted did not know at the time of her experiment that two species were involved, she cannot be sure how many of the newly-born spiders she interfered were cross-specific. The two species seem more or less equal in number, so chances are it was about half of them. If colony members are acting as foster mothers in the wild, something most odd is going on. Altruism(利他) is not a concept often associated with spiders. Xenophilic(种族间的) altruism is truly strange.
Which of the following explanations to social spiders is true?
选项 A、Different spiders within a colony act together and make individual contributions.
B、Spiders’ social groups are composed of closely related individuals.
C、Various spiders live in a public colony acting as a giant kindergarten.
D、Great similarities make spiders of different species live and hunt together.
答案C
解析 本题为四选一，找出对本文研究的该种社会性蜘蛛描述正确的一项，是基于事实的推断题，这种题型须认真看每个选项。选项C说明不同的蜘蛛生活的群落类似一个大型托儿所，第三段对蜘蛛的这种社会性进行可能的解释，即这一群体像是大型的托儿所，C项与原文一致。选项A认为生活在同一群落的不同蜘蛛一起工作、各有分工，而第六段段尾提到本实验研究的两种蜘蛛非常相似，这就排除了分工合作的可能性，因此A项与原文相反。选项B说明该种蜘蛛相互帮助并非奇特，而第六段段首提到群体内相互帮助的现象对种群动物并不罕见，不指该种蜘蛛，因此B项与原文相反。选项D说明不同蜘蛛共同生活觅食的原因是相似性，第六段中明确说明该蜘蛛群体由两种不同的蜘蛛组成，因此D项与原文相反。
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