千足虫

Millipede Gonopods

想发生性关系,却搞错了对象,这就很尴尬,好在大多数动物都能很好地避免这种失礼行为。但如果你是一只千足虫,生活在一块空间狭小、黑暗湿滑的岩石下,十几二十个物种都在四处奔跑,疯狂求偶,想要找准对象就不那么容易了。

幸运的是,小生物有应对方案:雄性千足虫进化出了复杂的生殖足,也就是说,它们的脚就是生殖器,上面还长着各种分枝、突起和刚毛。虽然千足虫有一万两千种,但没有哪两个品种的生殖足完全相同。因此这些小型节肢动物可以立即判断它们是否勾搭错了物种。这不仅方便了千足虫,也方便了生物学家。

芝加哥菲尔德博物馆的千足虫研究员佩特拉西尔瓦尔德说。你只需要拿来一只千足虫,看看它的腿说没错,就是这个品种。只需通过观察就能识别出来。唯一的问题是千足虫的生殖器很小。当然,说这话并没有冒犯男同胞的意思。你见过千足虫就知道,千足虫本来就小,可以想象,它们的腿更小。

你可能会说,谁在乎千足虫,更别说它们的生殖器了。其实,千足虫很重要。千足虫是最早的陆地动物,远古时期,受到美味的植物尸体引诱,才从水下来到了岸上。它们从事垃圾处理工作已经有四点六亿年,以吃腐烂植物为生,将养分回馈给土壤,而我们种植农作物正需要健康的土壤。问题是,现在没有足够的研究人员来确定千足虫种群是否稳定健康。西尔瓦尔德说,其实此刻有数千类未知品种的千足虫蠢蠢欲动,等待被发掘。

要统计新品种,还得回到生殖器。最近,西尔瓦尔德和同事们决定用紫外线照射菲尔德博物馆的千足虫藏品,因为这正是博物馆工作人员会做的事情。我们发现,千足虫生殖器会发光,而且颜色还不只一种,漂亮极了。千足虫生殖器的不同部位会发出不同颜色的荧光:蓝色、绿色、蓝绿色和黄色。这一发现发表在林奈学会动物学杂志上。

雄性生殖器为什么会发光,没人完全知道,也许连千足虫自己也不知道。但用颜色标记千足虫的私处,确实便于科学家们分辨不同的品种。西尔瓦尔德和同事目前正在着手研究不同品种的照片。我们需要大量雄性生殖器照片,在线等,急。这样一来,科学家就可以帮助千足虫保持土壤健康,千足虫好,我们也好。

原文

Most animals are pretty good at avoiding the embarrassing faux pas of having sex with the wrong species. But what if you’re a millipede under a cramped, dark, slippery rock with a dozen or more species all scurrying about, looking for love?

Fortunately, the critters evolved a solution: elaborate male gonopods—literally “genital feet”—with all manner of branches, bumps and bristles. And even with 12,000 species of millipedes, no two varieties of gonopods are exactly the same. So the little arthropods can immediately tell if they’re consorting with the wrong species—convenient not only for the millipedes, but also for biologists.

“So you just have to pick it up and look at it and you say, yup, that’s the species, and you can identify it.” That’s millipede researcher Petra Sierwald at the Field Museum in Chicago. The only problem is—no offense to any male millipedes—the gonopods are tiny. “If you look at a millipede, it’s not that big to begin with. So you can imagine their modified legs are even smaller.”

Now, before we go any further, you might be wondering, “Who cares about millipedes, let alone their genitals?” And the answer is, not enough of us. Millipedes are believed to be the first land animals, lured out of the water by tasty dead vegetable matter on earth’s primeval shores. “They have been in the business of waste management for 460 million years. And that means they are eating rotting vegetation. That returns the nutrients to the soil. And the healthy soil is what we need to grow our food.” But today there aren’t enough millipede researchers to determine if their populations are stable and healthy. In fact, Sierwald says there are thousands of unknown millipede species out there, just tapping their many, many, many, many feet, waiting to be noticed.

Which brings us back to gonopods. Recently Sierwald and her colleagues decided to shine ultraviolet light onto the millipede collection at the Field Museum, because that’s just exactly the sort of thing people who work in museums do. “We found that their copulatory organs fluoresce.” And not just with one color, which would have been cool enough. “Different parts of this copulatory organ will fluoresce in different colors: blue, greenish, bluish-greenish and yellow.” The finding is in the Zoological Journal of the Linnean Society.

As to why the male sex organs fluoresce, Seirwald says no one—perhaps not even the millipedes themselves—know for sure. But the color-coded private parts do make identifying millipedes much easier for scientists. Sierwald and her colleagues are now working to photograph different species. “We need pictures of the male gonopods, and we need them online, and we need them fast!” So that scientists can help millipedes keep the soil healthful, for them and for us.

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