内容来源：https://www.quantamagazine.org/the-jellies-that-evolved-a-different-way-to-keep-time-20260320/

内容总结：

科学家发现水母拥有独特生物钟：不依赖经典基因，按20小时周期运行

生命通常遵循着以24小时为周期的昼夜节律，这一由阳光校准的内在时钟广泛存在于从藻类到人类的生物中，其核心通常由CLOCK、BMAL1等一组保守基因掌控。然而，一项于2026年1月发表在《PLOS生物学》上的新研究揭示，自然界中存在着一套截然不同的计时系统。

日本宫城教育大学的出口龙作教授与其学生木津琉夏在研究一种暂被命名为“Clytia sp. IZ-D”的豌豆大小水母时，发现了令人惊奇的现象。这种水母并非在黎明后，而是在日落后约两小时进行集体产卵。实验室研究表明，在持续光照下，它们会以近乎精确的20小时为周期自主产卵，这表明其体内存在一个不依赖外界提示的内源性生物钟。

更引人注目的是，这种水母所属的水螅纲动物在进化过程中早已丢失了在其他动物中普遍存在的经典生物钟基因。这意味着，它们演化出了一套全新的分子机制来计时。研究人员推测，该机制可能与其近亲物种有所不同：日照可能触发一种激素缓慢释放，经过约14小时的积累促使配子成熟，最终在日落后启动同步产卵。这套机制就像一个由“20小时自主节律”与“14小时日照倒计时”组合而成的精密钟表。

这项发现挑战了生物钟研究的传统认知。未参与研究的伍兹霍尔海洋研究所学者安·塔兰特评价道，这项研究“非常激动人心”，它表明在丢失了所谓“必需”基因的动物体内，依然可以存在复杂的生物钟调节。莱斯特大学的生物钟学家埃齐奥·罗萨托指出，这一发现提示我们，生命之树上可能广泛存在着被忽视的非传统计时系统，“你可以用任何分子机制来制造一个时钟”。

目前，研究团队正计划通过基因组比对，进一步揭示这种独特20小时“类昼夜节律”与产卵倒计时器的分子基础。这项研究不仅拓展了人们对生物计时多样性的理解，也彰显了在经典模型之外探索生命奥秘所带来的惊喜。

中文翻译：

一种以不同方式演化出计时机制的水母

太阳东升西落——黎明、白昼、黄昏、黑夜——驱动着生命的时钟。有些物种日出而作，月升而息。另一些则恰恰相反，还有少数遵循着古怪的作息。这些由自然驱动、以24小时为周期的生物节律，被称为昼夜节律。它们的作用远不止提示就寝时间：它们还调节激素、新陈代谢、DNA修复等诸多生理过程。一旦生命节律失调，便可能对健康、繁殖和生存造成严重后果。

许多物种没有手表，它们依靠一套内部系统来计时——这是一套相互作用的基因及其蛋白质产物，能有效追踪24小时周期，并由阳光校准。这种昼夜节律钟分布广泛，甚至在单细胞藻类中也能找到，这表明生物计时机制在数十亿年前就已演化出来。纵观动物界，大多数物种拥有相同的遗传系统，使用名为CLOCK、BMAL1和CRY的基因或其可识别的同源基因。这种生物钟机制甚至在古老谱系（如海绵和某些水母）中就已出现。

但这是唯一的计时方式吗？在日本海岸附近一种豌豆大小的水母身上，生物学家正在研究一种不同的计时机制。

在水螅纲动物（包括某些种类的水母、水螅以及群体管水母，如葡萄牙僧帽水母）的演化历程中，它们丢失了动物界其他物种普遍拥有的、用于运作昼夜节律钟的基因。然而，一个新发现的水螅纲水母物种却拥有一个神秘的昼夜节律钟，它规律地追踪着20小时的周期，这表明其机制是独立演化出来的。这些发现于2026年1月发表在《公共科学图书馆·生物学》上，挑战了时间生物学家对“昼夜节律”的传统认知。

“我们一直想知道，水母真的有生物钟吗？”伍兹霍尔海洋研究所研究海葵昼夜节律的安·塔兰特（未参与此项研究）说，“这项研究非常令人兴奋，因为它展示了这种动物体内存在一个生物钟，而它丢失了我们认为在大多数其他动物中对于昼夜节律调节至关重要的那些基因。”

在这种对科学而言是全新的水母物种身上发现的生物钟非同寻常，不仅因为它追踪的是20小时周期，而非地球的24小时昼夜周期，还因为它似乎与一个分子计时器配对。这个计时器从日出开始倒计时，直到水母产卵的时刻。这种令人惊讶的机制表明，科学家们可能忽视了生命之树中各种非传统的生物钟。

“像这样的系统可能远比我们想象的更为普遍，而我们没有去寻找，因为我们只关注这些遗传成分[即动物的CLOCK基因等]，”莱斯特大学的时间生物学家埃齐奥·罗萨托（他为这项研究撰写了科学评论）说，“你可以用任何分子机制制造一个钟。你所需要的只是一系列以特定方式组织起来的化学反应。”

日出即开关

每季度一次，宫城教育大学的出口隆策都会带他的学生前往位于日本东北部海岸仙台湾的伊豆岛（面积约1平方英里）。在那里，渔码头下的水层中漂浮着成千上万颗比豌豆还小的透明球体。他和学生们采集这些代表十多个物种的水母样本，并在实验室中饲养，以研究它们的繁殖周期。

当贵水琉花还是大学新生时，他就是这些学生中的一员。在显微镜下观察水母配子发育的过程，将他从物理和化学的严谨逻辑中吸引出来，投身于生物学的动态过程。后来，他加入了出口的实验室，研究无脊椎动物的发育，并将他的硕士论文专注于水母繁殖，特别关注样本中一个特殊的群体。出口的许多水母每天都会产卵，通常在日出后不久将卵子和精子释放到水中。但这些水母很奇怪：它们在夜间产卵。

对于通过大规模产卵繁殖的物种（包括一些珊瑚和水母）来说，精确计时至关重要。它们直接将配子释放到水中，让受精听天由命：如果卵子到达时水中没有精子，就不会有下一代。因此，这些物种演化出了各种分子机制来同步产卵，通常利用能感知并响应光信号的蛋白质。

贵水知道，他的水母的日落时钟背后一定有某种分子机制。但缺乏明显的光触发因素，使得这种夜间产卵行为成了一个谜。

他从一系列光照实验开始。首先，他将雌性水母置于12小时人工光照和12小时黑暗的循环中——大致反映了伊豆岛的自然昼夜周期。每一次，在“黄昏”过后恰好两小时，雌性水母就会将卵子释放到水中。

起初，贵水和出口认为从光到暗的转变是产卵信号。但当他们将开灯时间提前两小时，使“黎明”更早到来而“黄昏”时间不变时，水母的产卵时间也提前了两小时。

在持续光照下，水母会怎么做？令贵水惊讶的是，水母在没有特定提示的情况下，自行每20小时产卵一次。这表明这种此前未知的水母物种（在获得正式命名前被称为Clytia sp. IZ-D）拥有某种内部驱动的昼夜节律。“在那一刻，我感受到了研究核心的真正快乐：揭示世界上此前无人知晓的事物，”他说。

贵水知道C. sp. IZ-D的时钟并非由动物界广泛存在的时钟基因构成；这个水螅纲谱系在演化过程中已经丢失了那些基因。然而，它几乎符合时间生物学家描述的所有关于昼夜节律钟的要求。

一个昼夜节律钟必须是自我维持且内部驱动的，正如水母产卵的20小时周期那样。它还必须受光等环境刺激调节；虽然水母的产卵钟在实验室持续光照下可以按20小时周期运行，但在自然界中，它每天都会重置。此外，一个真正的昼夜节律（像我们人类的一样）应该不受温度影响。然而，在贵水的实验中，水温升高会使20小时时钟变快，水温降低则使其变慢。它是一个分子生物钟，但并非科学家通常定义的那种。

“我想知道[这]在时间生物学领域将如何被看待，”阿尔弗雷德·魏格纳研究所和维也纳大学的时间生物学家克里斯汀·特斯马尔-雷布尔（未参与研究）说。如果它打破了三条规则中的任何一条，它还是一个真正的昼夜节律吗？“或者，我们作为一个科学共同体，会把它看作某种[别的]东西？”

但20小时的昼夜节律钟并不能完全解释水母的日落产卵行为。这个钟表机制中肯定还有另一个部分。

发射倒计时

为了更深入了解这个新物种的情况，出口和贵水转向了它的近亲——半球美螅水母。半球美螅水母在外观上与C. sp. IZ-D完全相同，都有一个透明的钟状体和长长的触手。关键的是，它是一个被充分研究的动物模型，其产卵和繁殖细节已广为人知。为了寻求答案，他们请来了他们的朋友、法国国家科学研究中心的发展生物学家、也是该物种的专家百濑毅。

每天，日出后两小时，半球美螅水母产卵。这个过程始于当天的第一缕阳光，此时生殖腺中被称为视蛋白的光感受蛋白检测到阳光，触发一种激素的产生，促使发育中的配子成熟。

研究团队推测，新物种C. sp. IZ-D拥有一个略微调整过的版本：激素随时间缓慢释放，将配子成熟过程延长至大约14小时。一旦积累了足够的激素且配子完全发育成熟，水母便会同步产卵——就像钟表一样精准，大约在日落后两小时。

“对我来说，作为一名时间生物学家，看到一个系统利用几乎与以前相同的工具，却达到了不同层次的组织水平，这非常有趣，”罗萨托说，“仅仅一点改变”——激素积累更慢，因此配子成熟过程更慢——“就创造了一个复杂得多的组织层次。”

接下来，百濑、出口和贵水计划比较半球美螅水母和C. sp. IZ-D的基因组，以探索在20小时准昼夜节律钟和14小时日出倒计时器中起作用的分子机制。2026年4月，贵水将在东北大学开始一个专注于蛤类繁殖的博士项目，在那里他可以继续描述无脊椎动物发育的奇特之处。

他所偶然发现的这个不寻常的时钟已经对该领域产生了影响。“这是一项非常出色的研究，将激发更多的工作，”塔兰特说，“它突显了生物钟机制的新颖性、多样性，或许还有完全不同的路径，并为我们提供了一些例子，展示了在研究这些机制时如何真正做到富有创造性。”

英文来源：

The Jellies That Evolved a Different Way To Keep Time
Introduction
The passage of the sun across the sky — dawn, day, dusk, night — drives the clock of life. Some species wake with the sun and sleep with the moon. Others do the opposite, and a few keep odd hours. These naturally driven, 24-hour biological cycles are known as circadian rhythms, and they do more than cue bedtime: They regulate hormones, metabolism, DNA repair, and more. When life falls out of sync, there can be dire consequences for health, reproduction, and survival.
Lacking watches, many species keep time using an internal system — a set of interacting genes and their protein products that effectively keeps track of a 24-hour period — that is calibrated by sunlight. This kind of circadian clock is widespread, found even in single-celled algae, which suggests that biological timekeeping evolved billions of years ago. Across animals, most species have the same genetic system, using genes known as CLOCK, BMAL1, and CRY, or recognizable homologues. This form of biological clock mechanism appears even in ancient lineages, including sponges and some jellyfish.
But is this the only way to do it? In a pea-size jelly off the coast of Japan, biologists are examining a different kind of timekeeping.
Somewhere over the course of their evolution, the class of hydrozoans — which includes certain kinds of jellyfish, hydras, and colonial siphonophores such as the Portuguese man-of-war — lost the genes that operate circadian clocks in the rest of the animal kingdom. Yet a newly discovered hydrozoan jellyfish species has a mysterious circadian clock that regularly tracks 20-hour periods, suggesting that its mechanism evolved independently. The findings, published in PLOS Biology in January 2026, push the limits of what chronobiologists consider “circadian.”
“We’ve wondered, do jellyfish have real clocks?” said Ann Tarrant, who studies circadian rhythms in sea anemones at the Woods Hole Oceanographic Institution and was not involved in the research. “This study is really exciting because it shows a clock in this animal that’s lost some of these genes that we think are essential for circadian regulation in most other animals.”
The clock found in this jellyfish, a new species to science, is unusual not only because it tracks 20 hours, instead of Earth’s 24-hour day length, but also because it seems to be paired with a molecular timer that counts down from sunrise until it’s time for the jellyfish to spawn. This surprising mechanism suggests that scientists may be overlooking unconventional clocks across the tree of life.
“Systems like this might be much more widespread, and we are not looking, because we only look at these genetic components, [the animal CLOCK genes],” said Ezio Rosato, a chronobiologist at the University of Leicester who penned a scientific commentary about the work. “You could make a clock with any molecular mechanism. All you need is a series of reactions which are organized in a certain way.”
A Light-Switch Sunrise
Once a quarter, Ryusaku Deguchi brings his students at Miyagi University of Education to Izushima, a 1-square-mile island in Sendai Bay along Japan’s northeastern coast. There, thousands of translucent orbs smaller than peas bob in the water column below the fishing dock. He and his students collect these jellyfish specimens, representing more than a dozen species, and rear them in the lab to study their reproductive cycles.
When Ruka Kitsui was a freshman in college, he was one of those students. Observing jellyfish gametes develop under a microscope lured him away from the neat logic of physics and chemistry and into the dynamic processes of biology. Later, he joined Deguchi’s lab to study invertebrate development and dedicated his master’s thesis to jellyfish reproduction, homing in on an unusual population among the specimens. Many of Deguchi’s jellyfish spawned daily, releasing their eggs and sperm into the water, usually shortly after sunrise. But these jellyfish were odd: They spawned at night.
For species that reproduce through mass spawning, including some corals and jellyfish, accurate timekeeping is crucial. They release gametes directly into the water, leaving fertilization to chance: If there aren’t sperm in the water when eggs arrive, there will be no next generation. So these species have evolved various molecular mechanisms to sync up their spawning, often using proteins that sense and respond to light signals.
Kitsui knew there had to be some molecular mechanism behind his jellies’ sundown clock. But the absence of an obvious light trigger made the night-spawning behavior a puzzle.
He began with a series of light experiments. First he kept female jellyfish in a cycle of 12 hours of artificial light and 12 hours of darkness — roughly reflecting the natural day-night cycle at Izushima. Each time, precisely two hours after “dusk,” female jellies released their eggs into the water.
At first, Kitsui and Deguchi assumed that the transition from light to dark was the spawning signal. But when they turned the lights on two hours earlier, making “dawn” happen sooner but leaving “dusk” at the same time, the jellyfish spawned two hours earlier as well.
What would the jellies do under continuous sunlight? To Kitsui’s surprise, the jellyfish spawned every 20 hours on their own, without a specific cue. This suggested that the previously unknown jellyfish species — dubbed Clytia sp. IZ-D until it receives a formal name — had some kind of internally driven circadian rhythm. “In that instant, I felt the true joy at the core of research: uncovering something that no one in the world had known before,” he said.
Kitsui knew that C. sp. IZ-D’s clock wasn’t made of the clock genes widespread in animals; this hydrozoan lineage had lost those over evolutionary time. Yet it fit nearly all the requirements that chronobiologists have described for circadian clocks.
A circadian clock must be self-sustained and internally driven, as the 20-hour cycle of the jellies’ spawning is. It must also be regulated by an environmental stimulus such as light; while the jellies’ spawning clock can run on a 20-hour cycle under persistent light in the lab, in nature it resets every day. And a true circadian rhythm, like ours, should also be unaffected by temperature. In Kitsui’s experiments, however, warmer water made the 20-hour clock faster and cooler water made it slower. It is a molecular biological clock, but not in the way scientists typically define them.
“I wonder how [this] will be perceived in the chronobiology field,” said Kristin Tessmar-Raible, a chronobiologist at the Alfred Wegener Institute and the University of Vienna who was not involved in the research. Is it a true circadian rhythm if it breaks any of the three rules? “Or will we, as a community, take it as something [else]?”
But the 20-hour circadian clock couldn’t fully explain the jellies’ sunset spawning behavior. There had to be another piece to this clockwork mechanism.
Countdown to Launch
To understand more about what was going on in their new species, Deguchi and Kitsui turned to Clytia hemisphaerica, a close relative. C. hemisphaerica is visually identical to C. sp. IZ-D, with a transparent bell and long, trailing tentacles. Crucially, it is a well-studied animal model, and the details of its spawning and reproduction are well known. Eager for answers, they pulled in their friend Tsuyoshi Momose, a developmental biologist at the French National Center for Scientific Research and an expert on the species.
Every day, two hours after sunrise, C. hemisphaerica spawns. This process begins with the day’s first light, when photoreceptive proteins called opsins in the gonads detect sunlight, triggering production of a hormone that matures developing gametes.
The team suspects that the new species C. sp. IZ-D has a slightly tweaked version of this mechanism in which the hormone is released slowly over time, dragging out the gamete maturation process to around 14 hours. Once enough of the hormone has accumulated and the gametes have fully developed, the jellies spawn simultaneously — roughly two hours after sunset, like clockwork.
“For me, as a chronobiologist, it is very interesting to see a system getting a different level of organization using almost the same tools that you had before,” Rosato said. “Just a little change” — slower hormone accumulation and therefore a slower gamete maturation process — “creates a much more complex level of organization.”
Next, Momose, Deguchi, and Kitsui plan to compare the genomes of C. hemisphaerica and C. sp. IZ-D to explore the molecular mechanisms at play in the 20-hour quasi-circadian clock and the 14-hour sunrise countdown timer. And in April 2026, Kitsui will start a doctorate program focused on clam reproduction at Tohoku University, where he can continue describing the quirks of invertebrate development.
Already, the unusual clock he stumbled upon has made an impact on the field. “It’s just a beautiful study that’ll inspire a lot more work,” Tarrant said. “It highlights that there’s novelty and diversity and perhaps completely different pathways, and it gives us some examples of how you can be really creative in studying those mechanisms.”