经济学人下载:节肢动物学 情人为食

Science and technology
科学技术

Arachnology
节肢动物学

Having a mate for dinner
情人为食

Male spiders make the supreme sacrifice for their children
雄蛛对后代的无私奉献

AMONG spiders, the female of the species really is more deadly than the male.
蜘蛛家族中,雌蛛致命性比雄蛛高得多。交配后将配偶狼吞虎咽地吃掉，雌蛛因此声名在外。

Lady arachnids have a well-deserved reputation for polishing off their suitors, post copula, in a manner that Hannibal Lecter might have admired.
它们的这一行为或许在一定程度上赢得了汉尼拔莱克特的敬仰，

But it has never been clear why this happens.
然而其原因一直不为人所知。

Some biologists believe it is simply a mixture of female hunger and the availability of a meal that is in no position to run away.
一些生物学家认为这仅仅是因为雌蛛饿了，而盘中餐又无力逃脱。

Others suspect that the male is actually sacrificing his life for the good of his genes.
一些生物学家认为雄蛛是为他的基因而牺牲的。

In other words, his becoming a meal for his paramour somehow helps the offspring of their union.
换句话说，他成为情人的腹中食某种程度上有助于他们共同的后代。

Peng Yu, of Hubei University in China, and his colleagues, decided to try to settle the question.
中国湖北大学的彭宇及其同事决定尝试解开这一谜题。

The results of their investigation are published this week in Behavioral Ecology and Sociobiology.
他们的条查结果刊登在《行为生态学与社会生物学》。

Dr Peng and his team collected almost 400 young wolf spiders, of both sexes, from local fields.
彭博士和他的小组在当地收集了几乎400只狼蛛，

They then raised the animals separately until they were sexually mature.
再雌雄分开饲养，直到它们性成熟。

Then, one at a time, they introduced the females to a male and watched until one of three things happened:
然后他们每次一只，将雌蛛与雄蛛配对，直到出现以下三者之一的情况发生：

the male got eaten; the male mated with the female and successfully avoided being eaten; or the male survived for half an hour, but did not mate with the female within that time.
雄蛛被吃；雄蛛与雌蛛交配后幸免于难；或者雄蛛存活了半小时，而期间未与雌蛛交配。有时，他们将未交配的雌雄蛛配对；

Sometimes the researchers paired virgin males with virgin females; sometimes they paired virgin males with females that had recently bred.
有时他们将未交配的雄蛛与刚繁殖过的雌蛛配对。

And in one crucial set of tests they paired virgin males with virgin females that had been taken off their regular diet of fruit flies a fortnight beforehand, and were thus presumed to be feeling more than a little peckish.
在一项关键性实验中，他们将未交配的雄蛛与停饲果蝇两周的雌蛛配对—此时假设雌蛛处于极度饥饿状态。

After doing all this, the team chose 16 females that had mated and then eaten their partners, and ten that had mated but not done so, and followed their reproductive success.
配对后，实验小组挑选了16只交配后吃掉配偶的雌蛛，10只交配后未吃掉配偶的雌蛛，观察其繁殖成功的过程。

When these females laid their egg sacs, the researchers picked ten sacs at random from each group and monitored those until the eggs hatched.
当这些雌蛛产下卵袋时，研究者从每组随机挑选了10个卵袋观察，直到卵孵化。

At that point they selected 20 spiderlings from each group for further study.
这时，他们从每组挑选10只幼蛛用于后续研究。

Their first pertinent observation was that, while female wolf spiders did indeed sometimes eat males before breeding with them, that happened only 10% of the time, and did not seem to be more frequent if the female had been starved.
他们第一个客观观察结果是，雌狼蛛有时确实会在交配前吃掉雄狼蛛，这种概率是10%，并且似乎不比雌蛛挨饿后比率高。

Their second observation was that if a male was deemed suitable to mate with, he was never eaten in copula—even though copulation could last as long as an hour and a half.
第二个观察结果是，如果雄蛛被认为适合交配，它们绝不会在交配中被吃—即使交配过程可能长达一个半小时。

Their third was that, 28% of the time, a male that had mated was indeed eaten afterwards.
他们第三个观察结果是，有28%的几率雄蛛会在交配后被吃。

Successful suitors, then, succumbed more often than unsuccessful ones.
如此可得出，交配成功的雄蛛被吃的比未成功的多。

The crucial finding, however—which makes sense of all the others—was the success of the spiderlings.
然而，幼蛛成活率是关键的发现—这使得其他发现都有了意义。

Young born of females that had eaten their partners had a 48% chance of making it through their first month of life.
吃掉配偶的雌蛛其后代48%可以活过一个月，

Those born of females who had let their partners live, had only a 12% chance of surviving that long.
而放生配偶的雌蛛的后代存活相同时间的只有12%。

That is a staggering difference—and certainly, in evolutionary terms, enough to drive self-sacrificial behaviour by males,
这个差距是巨大的—当然，按照进化论原则，足以使雄蛛采取自我牺牲行为。

since a male would have to mate successfully another three times to match the benefit he gains by this one suicidal act.
因此，为获得这一次自杀行为带来的好处，它之前必须成功交配三次。

The reason a male is almost three times as likely to be eaten if he has mated with the female in question than if he has not is thus probably that he wants to be eaten, for the good of his posterity.
讨论中，如果与雌蛛交配成功，雄蛛被吃的概率几乎是未交配成功的雄蛛的三倍，其原因可能是为后代着想，它希望被吃。

Just what it is that a male meal gives, via the female's digestive system, to the hatchling spiders, remains to be determined.
通过雌蛛的消化系统，雄蛛给予孵化蜘蛛的是什么？这还有待探索。

Perhaps spider bodies contain some crucial nutrients which are scarcer in other forms of prey.
也许蜘蛛体内含有其他猎物所缺乏的重要的营养成分。

Whatever the details, though, the general answer to the biologists' question is now clear.
不管具体如何，生物学家们的问题有了大致的答案。

In the case of spiders, fathers really do lay down their lives for their children.
对蜘蛛来说，父亲们真真是为孩子放弃了他们的生命。