| [♪ INTRO] While we’re pretty clear on the general idea of evolution, believe it or not, we still have plenty to learn about its specific mechanisms. In particular, there are still open questions around speciation, where one species diverges into two. And small, bioluminescent marine organisms called ostracods might hold the key to answering that question. If you go out just after sunset on a moonless night in the Caribbean, you might encounter these tiny crustaceans. Each one is no bigger than a grain of sand, but they produce their own blue light, which they blink on and off like fireflies. They do it by vomiting up little globs of glowing blue mucus, which light up for a few seconds before fading to black. While that sounds kind of gross, the light displays are key for male ostracods in attracting potential mates. This behavior is unique to the Caribbean ostracods. In other parts of the ocean, ostracods, both male and female, use their glowing blue vomit for defense, using it to distract potential predators. Light displays aren’t the only thing Caribbean ostracods are doing differently. Because ostracods in this particular region are split into a staggering number of species. Researchers describe this based on the relative proportions of the ostracods’ body parts, and by the size and shape of their reproductive organs. And, though not all have been formally described yet, researchers say they have found more than 100 species, all occupying roughly the same habitat. This is really strange, because normally, you wouldn’t expect to see so many similar species living in the same place. To understand why, we have to think about what a species is. Historically, we’ve often defined species as groups of animals that both can and do reproduce with each other and produce fertile offspring. Species usually form when a population becomes somehow cut off from others of its kind and can no longer interbreed with them. One gene pool becomes two, and different changes start to accumulate in each. But the Caribbean ostracods aren’t isolated from each other, at least not physically. They live in the same place and share the same resources. But they’re still made up of hundreds of populations that don’t interbreed. So the question is, what’s stopping them? Scientists think that the mating displays might have something to do with it. These displays might actually be leading to the formation of new species. They think this might be due to a phenomenon called sexual selection. This is a phenomenon that was first described by Charles Darwin himself, and nowadays is often talked about in species with courtship displays. Basically, it’s the idea that the traits that are passed onto future generations are dependent on what females of a species look for in eligible mates. For example, if females of a species choose a mate based on the brightness of his feathers, males of that species will pass on genes that lead to brighter feathers over time. This is related to natural selection, the idea that traits that get passed on in species are the ones that make an organism more likely to reproduce in the first place. But while natural selection is a well established phenomenon, we still have some questions about sexual selection, especially whether it actually drives the creation of new species out there in the real world. Ostracods are a particularly elegant way to test this phenomenon. Since they don’t live for very long, it’s possible to study multiple generations in the lab. And since their light displays are fairly simple as far as mating displays are concerned, it’s not hard for researchers to map them out and find the differences between them. Of course, to do all this you’d have to be able to breed ostracods in the lab, something we’ve only learned how to do recently, and are still perfecting. But now that we can, we can look into what’s driving ostracods in the Caribbean to split off into new species what seems like every other week. To do that, researchers have been looking at the ostracods’ RNA. Since cells use RNA to generate messages of the genes they’re actively using, the transcriptome, or sequence of a species’ RNA transcripts, is a shortcut to finding meaningful differences in DNA. They looked at those differences, plus the morphology data they already had, to figure out which groups were different enough from each other to count as a different species. They then compared records from Caribbean ostracods to ostracods in other parts of the world. They even looked at the fossil record, to look at ostracods that are now extinct, and put together a sort of family tree to see how closely these different species are related to each other. They found that ostracod groups that use light for mating displays tend to form new species faster than groups that don’t. That lends some support to the idea that’s it’s all about sexual selection, because while all these species are bioluminescent, it’s the ostracods with mating displays that are diverging. See, when a lot of ostracods live together, their mating displays are much more elaboratethan when they live alone. That helps them stand out from the crowd, to better attract mates. But as these groups form more and more elaborate displays, they start isolating themselves into groups. And the more isolated each group is, the more likely a new species is to form. The next step in this research would be to sequence the full ostracod genome. That means mapping out all of the ostracods genes, not just the ones each species is currently using. This isn’t trivial, though. The ostracod genome is longer than our own. But by doing this, researchers hope to compare the genomes of different ostracod species, to figure out exactly how these species diverge. That can help us figure out whether sexual selection really can make new species, answering a long-standing question about one of Charles Darwin’s evolutionary theories. These results could be applied not just to ostracods, but also to other forms of life. And if you want to keep learning about other bioluminescent forms of life, then you should watch the Bizarre Beasts video on New Zealand glowworms. You might just get sucked into a new show created by some of the same people who make SciShow! You can learn about all kinds of Bizarre Beasts from frogs that can’t land their own jumps to lizards with legs in the front and a wormy behind. Join hosts Hank Green and Sarah Suta to explore what makes these animals so weird to us. And if one, or all, of them particularly strikes your fancy, you can take it home through the Bizarre Beasts pin club! Profits go toward our community’s efforts to decrease maternal mortality in Sierra Leone. The links for the channel and the pin club are in the description below! [♪ OUTRO] | [♪ 简介] 尽管我们对进化的一般概念非常清楚 ，但不管你信不信， 我们仍然有很多关于其具体 机制的知识。 特别是， 关于物种形成的问题仍然悬而未决， 其中一个物种分化为两个。 被称为介形虫的小型生物发光海洋生物 可能是回答这个问题的关键。 如果你在加勒比海的一个没有月亮的夜晚日落后刚出门 ， 你可能会遇到这些微小的甲壳类动物。 每个都不比一粒沙子大， 但它们会产生自己的蓝光， 它们像萤火虫一样闪烁。 他们通过吐出一小团 发光的蓝色粘液来做到这一点， 这些粘液会亮几秒钟，然后 逐渐变黑。 虽然这听起来有点恶心 ，但灯光显示是雄性介形类 动物吸引潜在配偶的关键。 这种行为是加勒比介形虫独有的。 在海洋的其他地方，介形虫，无论是 雄性和雌性，都 使用它们发光的蓝色呕吐物进行防御， 用它来分散潜在捕食者的注意力。 灯光展示并不是加勒比 介形类动物唯一与众不同的地方。 因为这个特定区域的介形类 被分成数量惊人的物种。 研究人员根据 介形类动物身体各部分的相对比例， 以及它们生殖器官的大小和形状来描述这一点 。 而且，虽然还没有对所有物种进行正式描述， 但研究人员表示，他们已经发现 了 100 多种物种，它们都占据着 大致相同的栖息地。 这真的很奇怪，因为通常情况下， 你不会期望看到这么多相似的 物种生活在同一个地方。 要理解为什么，我们必须考虑 什么是物种。 从历史上看，我们经常将物种定义 为 能够并且确实能够相互繁殖 并产生可育后代的动物群体。 当一个种群 以某种方式 与其他同类隔绝并且不能再 与它们杂交时，通常会形成物种。 一个基因库变成两个，不同的变化 开始在每个基因库中积累。 但是加勒比介形类动物并不是 彼此孤立的，至少在身体上不是孤立的。 他们住在同一个地方，共享 相同的资源。 但它们仍然由数百个 不杂交的种群组成。 所以问题是，是什么阻止了他们？ 科学家们认为交配展示 可能与此有关。 这些展示实际上可能会导致 新物种的形成。 他们认为这可能是由于一种 叫做性选择的现象。 这是查尔斯·达尔文本人首先描述的一种现象 ，如今在具有求爱表现的物种中经常被谈论 。 基本上，传递给后代的 特征取决于一个物种的雌性 在合格配偶中寻找什么。 例如，如果一个物种的雌性 根据羽毛的亮度选择配偶，那么随着时间的推移 ，该物种的雄性将传递 导致羽毛更亮的基因。 这与自然选择有关， 即在物种中传递的特征首先 是使生物体更有 可能繁殖的特征。 但是，虽然自然选择是一个公认的 现象， 但我们仍然对性选择有一些疑问 ， 尤其是它是否 真的在现实世界中推动了新物种的创造。 介形虫是测试这种现象的一种特别优雅的方法 。 由于它们的寿命不会很长，因此 可以在实验室中研究多代。 它们的光显示相当简单，因此研究人员不难将它们绘制 出来并找出它们之间的差异。 当然，要做到这一切，你 必须能够在实验室中培育介形类动物， 这是我们最近才学会的， 而且还在不断完善中。 但现在我们可以了，我们可以研究是什么 驱使加勒比地区的介形类动物每隔一周 分裂成新物种 。 为此，研究人员一直 在研究介形类动物的 RNA。 由于细胞使用 RNA 来生成 它们正在积极使用的基因的信息 ，因此转录组或一个物种的 RNA 转录物序列 是在 DNA 中发现有意义差异的捷径 。 他们查看了这些差异，加上 他们已有的形态学数据， 以找出哪些群体 彼此之间的差异足以算作一个不同的物种。 然后，他们将加勒比 介形类动物的记录与世界其他地区介形类动物的记录进行了比较。 他们甚至查看了化石记录， 查看现已灭绝的介形类动物，并 整理了一种家谱，以了解这些 不同物种之间的关系有多密切。 他们发现，使用光进行交配展示的介形类动物群体往往比不使用光 的 群体更快地形成新物种 。 这为性选择的观点提供了一些支持 ， 因为虽然所有这些物种都是生物发光的， 但具有交配表现的介形类动物正在分化。 你看，当许多介形类动物生活在一起时，它们的交配表现比它们单独生活时要复杂得多。 这有助于他们从人群中脱颖而出 ，更好地吸引配偶。 但随着这些群体形成越来越精细的展示， 它们开始将自己隔离成群体。 每个群体越孤立 ，形成新物种的可能性就越大。 这项研究的下一步是对 完整的介形类动物基因组进行测序。 这意味着绘制出所有的介形类 基因， 而不仅仅是每个物种目前正在 使用的基因。 不过，这并非微不足道。 介形类基因组比我们自己的更长。 但通过这样做，研究人员希望比较 不同介形类物种的基因组， 以弄清楚这些物种究竟是如何分化的。 这可以帮助我们弄清楚性 选择是否真的可以创造新物种，从而 回答一个 关于查尔斯达尔文进化论的长期问题。 这些结果不仅可以应用于 介形类动物，还可以应用于其他形式的生命。 如果您想继续了解其他 生物发光生命形式， 那么您应该观看有关新西兰萤火虫的奇异野兽视频 。 您可能会被一些制作 SciShow 的同一个人制作的新节目所 您可以了解各种奇异的野兽，从 不能自己跳跃着陆的青蛙 到 前腿后腿长虫的蜥蜴。 与主持人 Hank Green 和 Sarah Suta 一起探索 是什么让这些动物对我们如此奇怪。 如果其中一个或全部特别吸引 您， 您可以通过 Bizarre Beasts 图钉俱乐部将其带回家 ！ 利润将用于我们社区 为降低塞拉利昂孕产妇死亡率所做的努力。 频道和pin club的链接 在下面的描述中！ [♪结尾] |
