科学家现在认为，雄性有意选择在交配前吃的肚大腰圆的“胖”雌性作为追求对象（图）
北京时间8月11日消息，科学家表示，雄性黑寡妇蜘蛛会选择那些刚刚进过食的雌性作为交配对象，以避免自己变成它们的口中餐。
众所周知，雌性黑寡妇蜘蛛在交配结束后，会立刻吃掉它们的交配对象。现在研究人员认为，雄性为了避免这种悲剧发生，会选择在交配前吃的肚大腰圆的“胖”雌性作为追求对象。美国内布拉斯加大学的这一发现，显示了性别之战出现的罕见转变，雄性具有自由挑选交配对象的优势。
研究人员艾琳-赫伯兹说：“大部分时间人们都把注意力集中在雌性身上。很少会有人把雄性视为一个潜在的挑选发起者。”科学家前往亚利桑那州，研究北美黑寡妇Latrodectus hesperus。他们在那里发现，雄性黑寡妇能发现雌性蛛网上的泄密化学物质，通过这些物质，它们能够判断出雌性是否已经吃饱，以提高它们在交配后不被吃掉的概率。
另一个优势是雄性黑寡妇喜欢挑选体型较大的雌性，这样的雌性可能携带的卵子更多。研究负责人扎德-约翰逊说：“这是个双重打击。”他解释说，对雄性黑寡妇来说，交配的风险非常大，以至于自然迫使它们做出额外选择。约翰逊博士和他的科研组通过4项试验对这进行检验。
第一项试验显示，雄性更喜欢向蛛网上空空如也的雌性求爱，因为它们已经吃饱；第二项试验期间，科学家把雌性蜘蛛放在上面，结果雄性再次挑选了它们。在进行第三项试验时，科学家把饥肠辘辘的雌性蜘蛛放在吃饱的雌性蛛网上，或者把吃饱的雌性放在腹中空空的雌性蛛网上，结果显示，雄性对它们没有特别的偏爱。
在第四项试验时，研究人员把饱餐后和饿肚子的雌性蜘蛛的网分别粘在一根木棒上，并看到雄性选择了沾着饱餐后的雌性蜘蛛的蛛网的木棒。通过这些试验他们得出结论，饱餐后的雌性留在蛛网上的化学物质，对潜在的求爱者具有很大吸引力。约翰逊说：“雄性黑寡妇并不服从命运的安排。它在努力让糟糕的环境尽量变得最有利于自己。”
生物探索推荐英文原文
Male black widows prefer to mate with females who have just eaten
(so they don't become her next meal)
Male black widow spiders select mates who have recently fed to avoid getting eaten themselves, according to scientists.
Female black widows are well-known for feeding on their partners immediately after sex.
Now researchers believe the male of the species deliberately seeks out a 'fat' female who is full-up before mating.
The findings by scientists at the University of Nebraska reveal a rare turnaround in the sexual power struggle in which the male of the species has the advantageous power of selecting a mate.
Researcher Eileen Hebets said: 'Most of the time people focus on females. It's much less common to think of males as a potential source of selection.'
The scientists travelled to Arizona to study the North American black widow, Latrodectus hesperus.
There, they discovered that male black widows can detect tell-tale chemicals on the webs of females - these let them know if they are well-fed or not and therefore improves their chances of not getting eaten.
Another advantage is that in choosing a larger lady, the male black widow is increasing the chance of a mate with a large number of eggs.
Lead researcher Chad Johnson told Inside Science News Service: 'It's a double whammy.'
He explained that the danger of mating is so great for males, that nature forces them to be extra selective.
Dr Johnson and his team tested this with four experiments.
The first saw that males were more likely to court on the empty webs of well-fed females; the second added the females to their webs and again the males chose them.
The third experiment saw the scientists put hungry females on the webs of well-fed females and vice versa - the males showed no particular preference.
Lastly, the researchers rolled webs from both well-fed and hungry females onto separate sticks and watched the males choose the 'well-fed web' sticks.
From this, they concluded the webs must contain a chemical left by a well-fed female that is attractive to would-be suitors.
Dr Johnson said: 'The black widow male is not at all complicit in his own demise. He's making the best of a bad situation.'
