Biologists have identified a third species—a yeast—in some lichens, shaking up what's always been known as a two-party system. Christopher Intagliata reports. 

生物学家在地衣中分离出第三类生物——酵母，这个发现动摇了地衣只有两种系统的学说。克里斯朵夫˙因塔利亚塔（Christopher Intagliata）报道。

撰文/播音 克里斯朵夫˙因塔利亚塔（Christopher Intagliata）

翻译 郭丰茹

校对 丁可含

Lichens. They’re probably the most common example of two organisms living in a symbiotic relationship. There’s a fungus and a photosynthesizing partner, like algae. It's a bond that was born, as they say, when "Alice Algae," took a "lichen" to "Freddie Fungus."

地衣（Lichens）可能是两种生物共生关系的常见例子。有真菌和光合作用生物，例如蓝藻。它们生来就是一个结合体，正如生物学家们所说，“爱丽丝蓝藻”（Alice Algae）将“地衣”（lichen）带给了“弗兰迪真菌”（Freddie Fungus）。

But that simple description covered up a larger mystery: how could two different lichen species combine the same building blocks—same fungus, same algae—“and yet they look very different, have very different chemistry, and some of them even have distinctly different ecology."

这个简单的比喻涵盖了一个惊人的奥秘：两种不同的生物是如何结合在一起构建出一个完整的地衣团块的呢？一种真菌、一种蓝藻，“但它们之间形态、化学（chemistry）组成很不一样，其中一些甚至有着截然不同的生态环境（ecology）。

Toby Spribille, an evolutionary biologist at the University of Montana, and the University of Graz in Austria.

托比˙斯普利比尔（Toby Spribille）是蒙大拿大学（University of Montana）和格拉茨奥地利大学（University of Graz in Austria）的演化生物学家（evolutionary biologist）

He and his colleagues studied two lichen species that fit that bill. Same underlying parts, different color and chemistry. They ground the lichens up, and then analyzed their RNA. What they expected to find was two genomes: one fungus, one alga. "And what we found was, at the end of a lot of analysis, what we had was three genomes, not two."

他以及他的同事研究了两种符合以上现象的地衣类群——相同的基础成分，颜色和化学组成不同。他们将地衣研碎，分析它们的RNA。预期分离出两种基因组（genomes）：一种是真菌的，一种是蓝藻的。“但出乎意料的是，经过大量的分析之后，我们发现了三种，并非两种。”

The third genome was from a type of yeast. And the more yeast was present, the more yellowish—and more toxic—the lichen was. The study appears in the journal Science. [Toby Spribille et al., Basidiomycete yeasts in the cortex of ascomycete macrolichens]

第三种基因组是酵母（yeast）的。而且酵母越多，地衣颜色越黄，毒性越强。这项研究见报于《自然》杂志（journal Science）。[Toby Spribille et al., Basidiomycete yeasts in the cortex of ascomycete macrolichens]

But how could scientists spend so many years studying these lichens—and still miss this crucial third species? Spribille says it could have been the type of genetic sequencing. Previous studies relied on DNA barcodes, which only sample some of the genome, to identify the underlying fungus and alga. Sort of like identifying the occupants of a completely dark room by shouting out a few names and seeing who answers.

但科学家们历经多年研究地衣怎么会忽略如此关键的第三种生物呢？斯普利比尔说可能是由于基因测序（genetic sequencing）的方式。当前的研究主要基于DNA编码（DNA barcodes），但这仅仅可以鉴定真菌和蓝藻。就好像在一个漆黑的屋子里找人，喊出几个名字，等着看谁来答应。

What Spribille did, instead, was just turn all the lights on, with whole genome sequencing, revealing the identity of all occupants, and in doing so, "we eliminated anything that required going in and calling out somebody's name so to speak."

斯普利比尔所做的工作相当于将室内所有的灯打开，进行全基因组测序，曝光所有的人确切身份，这样“我们不用进屋子呼唤名字等着应答。”

As for whether some lichens might have four, five species? "I certainly wouldn't rule it out at this point." Because this study indicates lichens are truly more than the sum of their parts. Including, of course, the parts we still don't know about.

那么，是否地衣可能有四种或者五种生物共生？“我确实不能排除这个可能。”因为这项研究表明地衣并非是几种生物的简单组合，况且我们还不完全清楚它的组成部分。

—Christopher Intagliata