冬虫夏草

Zombie Ants

这简直就像恐怖片里的桥段。一只蚂蚁被真菌感染后,举止怪异,一路爬到树顶,抓住一片树叶或一根树枝就放嘴里使劲咬。宾州的一名分子生物学家曼歌德将其称为死亡之咬。蚂蚁一旦出现这种怪诞行为,数小时之后就会死亡。

这种真菌叫冬虫夏草,它会吃空蚂蚁的血肉,然后从蚂蚁的躯壳中生发出一根茎,释放大量孢子,感染其它蚂蚁。这种现象真的很残忍。这样不好,太残忍了。蚂蚁为什么会这样,为什么会出现死亡之咬,曼歌德和同事想一探究竟,他们肢解了被真菌感染的蚂蚁,然后用电子显微镜放大观察了蚂蚁的下颌肌肉。

结果发现真菌入侵了蚂蚁的身体,长进了蚂蚁的下颌肌肉细胞里,很可能是为了吸收蚂蚁的营养。他们还发现了大量的神秘微粒,这些微粒可能是蚂蚁免疫系统释放出来的,也可能是真菌为了与肌肉交流沟通,从而强迫肌肉收缩而释放出来的。不管这之间存在什么沟通机制,研究人员发现蚂蚁的下颌肌肉会剧烈收缩,以至于彻底损坏,无法修复。这项研究的全文和暴力血腥的配图发表在实验生物学杂志上。

曼歌德想进一步研究那些神秘微粒的作用。同时,你我大可不必担心,这种真菌影响的只是个别的物种,比如木蚁。所以近期不可能真的出现僵尸人。

原文

It's straight out of a horror movie: an ant, infected with a fungus, starts behaving strangely. It crawls as high as it can in the forest, grabs a leaf or twig in its mouth and bites. Hard. "It enters into this 'death-grip phenotype' is what we call it." Colleen Mangold, a molecular biologist at Penn State. "And then a couple hours after initiation of that behavior the ant will die."

The fungus, known as Ophiocordyceps, then eats through the corpse and sprouts a stalk from the ant's body to release more spores and infect more ants. It's a harsh way to go. "It's not ideal, definitely not ideal." Mangold and her colleagues wanted to get to the bottom of why the ants do this—specifically, how they get their death grip. So they dissected infected ants and zoomed in on their jaw muscles with electron microscopes.

They saw that the fungus had invaded and grown into jaw muscle cells, perhaps to suck up nutrients. And they spotted lots of mysterious tiny particles, which might be produced by the ant's immune system—or by the fungus, as a way of communicating with the muscle and forcing it to contract. Whatever the mechanism, they found that the ant's jaw muscles had contracted so hard, they'd been irreparably damaged. The full details—and gory pictures—are in the Journal of Experimental Biology.

Mangold hopes to get to the bottom of what those tiny particles do in follow-up work. And in the meantime, unless you're a carpenter ant, rest assured you have nothing to worry about. "It's highly species specific. I seriously doubt we'll be seeing any real-life human zombies anytime soon."

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