蚂蚁是如何免遭驱逐的

For ant larvae and pupae, getting sick is a death sentence. When adult ants spot an infirm individual in their spotlessly clean nest, they simply chuck it out and leave it to die. This extreme “hygienic behavior,” as it’s technically called, is an effective way of containing disease outbreaks in crowded insect colonies. But some pupae have worked out a way to avoid nest eviction—by growing inside bug-proof cocoons and dodging disease, reports a study published this week in BMC Evolutionary Biology. Scientists have long wondered why in some ant species the pupae spin silk cocoons around their bodies, whereas in others the pupae are “naked.” In a few odd cases, ants can even swing both ways: In the same species, some pupae build cocoons, but others live happily without one. Or maybe not. When researchers infected different ant species (with cocooned, naked, or indecisive pupae) with a deadly fungus, the adults swiftly removed the diseased brood from the nest. However, cocooned pupae were often left behind, and even though they remained exposed to the fungus, they didn’t get sick. The authors conclude that cocoons act as shields against fungal invasion. It’s a win-win situation for the ants: The pupae don’t get sacrificed and the colony stays safe from an epidemic. 

 对于幼蚁和蚁蛹来说，一旦得病就等于是判了死刑。当成年蚂蚁在它们那一尘不染的蚁穴里发现虚弱的幼蚁或蚁蛹之后，它们就会将之清理出去，任其死亡。这在技术上被称为“卫生行为”，而这种极端的行为是一种行之有效的方法，可以控制疾病在拥挤的昆虫种群中爆发。然而，研究人员在本周发表于《BMC进化生物学》杂志上的一篇研究论文中报道说：一些蚁蛹想出一个办法，可以免遭清除——它们内部长出防止病菌的茧，避免生病。长期以来，科学家们一直想知道这个问题：为什么某些种类的蚁蛹吐丝作茧，缠绕身体，而其他种类的蚁蛹则是“光身”的？在一些奇特的情况下，可能会两种情况兼而有之：在同一种蚂蚁中，有的蚁蛹作茧缠身，有的蚁蛹在没有作茧的情况下快乐地生活着。或者，没有作茧的蚁蛹也许不会那么快乐。当研究人员让不同种类的蚂蚁（包括作茧的、光身的或不确定是否作茧的）感染上一种致命的真菌后，成年蚂蚁很快将染病蚁蛹从巢穴中清理出去。而那些作茧的蚁蛹总是被留下来，即使继续暴露于真菌中，它们仍不会染病。论文的作者们得出结论：蚁蛹的作茧行为就是为了防止真菌的侵袭。这对于蚂蚁来说是一种双赢的局面：蚁蛹不会被处死，而面临流行病的整个种群可以安全地留下来。