Parasitic zombie-ant fungus thrives in mosses, too
Parasitic zombie-ant fungus thrives in mosses, too
寄生性“僵尸蚂蚁”真菌也能在苔藓中繁衍
The parasitic fungi in the Cordyceps genus are a favorite subject of nature documentaries. They’ve also infiltrated popular culture via the zombie-apocalypse video game The Last of Us (2013) and its TV adaptation, in which a parasitic fungus mutates to infect humans. Scientists are keen to study Cordyceps to learn more about the origins and intricate mechanisms underlying these pathogen-based diseases. 虫草属（Cordyceps）的寄生真菌是自然纪录片中的热门题材。它们也通过僵尸末日题材电子游戏《最后生还者》（2013）及其电视剧改编版渗透到了流行文化中，在这些作品里，一种寄生真菌发生变异并感染了人类。科学家们热衷于研究虫草属，以深入了解这些基于病原体的疾病的起源和复杂机制。
The latest finding: DNA analysis revealed the same fungus in both parasitized insects and surrounding mosses, according to a paper published in the journal IMA Fungus. (Yes, really.) This suggests a second life stage during which the fungus lives inside the moss, possibly an evolutionary adaptation to survive when insect hosts may be scarce. It could also explain why the host species seems to prefer biting into mosses during their final death throes. 最新的发现是：根据发表在《IMA Fungus》期刊上的一篇论文，DNA分析显示，在被寄生的昆虫和周围的苔藓中存在同一种真菌。（没错，是真的。）这表明该真菌存在第二个生命阶段，即生活在苔藓内部，这可能是为了在昆虫宿主稀缺时生存下来而演化出的适应性。这也可能解释了为什么宿主在临死前的挣扎阶段似乎更倾向于咬住苔藓。
As we’ve previously reported, there are more than 400 different species of Cordyceps fungi, each targeting a particular insect species, like ants, dragonflies, cockroaches, aphids, or beetles. The spores attach to the target insect, such as a carpenter ant, and germinate, spreading through the host’s body via long tendrils called mycelia. Cordyceps essentially turns its host into a zombie slave, compelling the ant to climb to the top of the nearest plant and clamp its tiny jaws in a death grip around a leaf or twig. 正如我们之前报道的那样，虫草属真菌有400多种，每种都针对特定的昆虫物种，如蚂蚁、蜻蜓、蟑螂、蚜虫或甲虫。孢子附着在目标昆虫（如木匠蚁）身上并萌发，通过被称为菌丝的长丝状结构在宿主体内扩散。虫草本质上将宿主变成了僵尸奴隶，迫使蚂蚁爬到附近植物的顶端，并用细小的下颚死死咬住叶子或细枝。
The fungus then slowly devours the ant, sprouting through its head in one final indignity. The bulbous growths on the ends of the mycelia burst, releasing even more spores into the air to infect even more unsuspecting ants. It’s not a great way to go: The entire process can take four to 14 days. 随后，真菌会缓慢地吞噬蚂蚁，并从其头部破体而出，完成最后的一击。菌丝末端的球状生长物破裂，将更多的孢子释放到空气中，以感染更多毫无防备的蚂蚁。这并不是一种好的死法：整个过程可能需要4到14天。
Prior research showed that the zombification might be due to the release of a special chemical that causes the muscles in the infected ants’ mandibles to contract forcefully for that death-grip bite. A 2017 study found that the fungal cells formed an elaborate, interconnected 3D network, enabling them to communicate and exchange nutrients. They essentially cut the brain off from the rest of the ant’s body so the networked cells can control its behavior. 先前的研究表明，这种“僵尸化”可能是由于释放了一种特殊的化学物质，导致受感染蚂蚁下颚的肌肉强力收缩，从而形成那种致命的咬合。2017年的一项研究发现，真菌细胞形成了一个复杂且相互连接的3D网络，使它们能够进行交流和交换营养物质。它们本质上切断了大脑与蚂蚁身体其余部分的联系，以便网络化的细胞能够控制其行为。
And in 2019, scientists found that the fungus doesn’t actually directly attach to an infected ant’s brain. Rather, it breaks apart the membrane that covers jaw-muscle fibers, causing contractions strong enough to damage or destroy the muscle filaments that slide past each other when the muscles contract. 而在2019年，科学家们发现，真菌实际上并没有直接附着在受感染蚂蚁的大脑上。相反，它破坏了覆盖在下颚肌肉纤维上的膜，导致肌肉收缩力过强，从而损坏或摧毁了肌肉收缩时相互滑动的肌丝。
A hidden stage
隐藏的阶段
There is growing evidence that these kinds of fungal pathogens can expand their host range to adapt to a scarcity of hosts or environmental stress. For example, one species colonizes plant roots and can also parasitically infect cyst nematode eggs. Most relevant to this latest paper is recent research on insect-parasitizing fungi that have evolved to exploit both plants and arthropods. This includes a 2020 Chinese study in which the “Himalayan gold” (O. sinensis) fungal species (which targets ghost moth larvae) was found lurking in plants in alpine regions. 越来越多的证据表明，这类真菌病原体可以扩大其宿主范围，以适应宿主稀缺或环境压力。例如，某一种真菌可以定植在植物根部，也能寄生感染胞囊线虫卵。与这篇最新论文最相关的是近期关于昆虫寄生真菌的研究，这些真菌已经演化出既能利用植物又能利用节肢动物的能力。这包括2020年的一项中国研究，该研究发现“喜马拉雅黄金”（冬虫夏草，O. sinensis，针对蝙蝠蛾幼虫）真菌物种潜伏在高山地区的植物中。
There have also been reports of ant-infecting Ophiocordyceps species showing a seeming preference for specific plants, like understory palm trees and moss carpets, as death sites for their unfortunate hosts. For this latest study, the authors collected samples from “ant graveyards”—sites littered with the corpses of Ophiocordyceps-infected ants—at the Adolpho Ducke Forest Reserve in Brazil’s Central Amazon region. 还有报道称，感染蚂蚁的偏侧蛇虫草属（Ophiocordyceps）真菌似乎偏好特定的植物，如林下棕榈树和苔藓地毯，作为其不幸宿主的死亡地点。在这项最新研究中，作者从巴西中部亚马逊地区的阿道夫·杜克森林保护区（Adolpho Ducke Forest Reserve）的“蚂蚁墓地”（散布着被偏侧蛇虫草感染的蚂蚁尸体的地点）收集了样本。
There were four sample categories: fungi emerging from infected insects, mosses located where the ants were bitten, mosses adjacent to biting sites, and a control group of mosses at least 10 meters away from biting sites with no evidence of infected insect bodies. All samples were photographed and cleaned of debris, placed in tubes, and stored in a freezer for DNA extraction and analysis. 样本分为四类：从受感染昆虫中长出的真菌、蚂蚁被咬住位置的苔藓、咬合点附近的苔藓，以及距离咬合点至少10米且没有受感染昆虫尸体迹象的对照组苔藓。所有样本都经过拍照、清理杂物、放入试管，并储存在冷冻柜中以进行DNA提取和分析。
The authors identified 19 Ophiocordyceps-infected insects, all but three of which were infected with the “zombie-ant” fungi in the first group—mostly ants, but also a weevil, a plant hopper, and a firefly larva. The majority (11 of 19) of the infected insects were found attached to mosses; one had bitten into liverwort as well as moss, and a handful of specimens were embedded in carpets made of several different kinds of mosses and liverworts. 作者鉴定了19只感染了偏侧蛇虫草的昆虫，除3只外，其余均感染了第一组中的“僵尸蚂蚁”真菌——主要是蚂蚁，但也包括象鼻虫、叶蝉和萤火虫幼虫。大多数（19只中的11只）受感染的昆虫被发现附着在苔藓上；其中一只不仅咬住了苔藓，还咬住了地钱，少数样本则嵌入在由几种不同类型的苔藓和地钱组成的毯状物中。
The team also identified Ophiocordyceps in the actual mosses, suggesting that the ants’ preference for those mosses when choosing the site for their “death grip” might be another form of manipulation by the parasitic fungus. 研究小组还在这些苔藓本身中发现了偏侧蛇虫草，这表明蚂蚁在选择“死亡咬合”地点时对这些苔藓的偏好，可能是寄生真菌操纵的另一种形式。
“We have always thought of this fungus (Ophiocordyceps) as a parasite exclusive to insects, especially the ones it manipulates,” said co-author Tales Alves Jr. of Instituto Nacional de Pesquisas de Amazonia in Brazil. “What our data suggest is that the story is much larger: The same fungus appears to be ubiquitous in the surrounding moss communities. Our results illustrate a far closer link between the lifecycles of the plants and fungi involved in the behavioral manipulation of Amazonian ants.” “我们一直认为这种真菌（偏侧蛇虫草）是专门寄生于昆虫的，尤其是它所操纵的那些昆虫，”巴西亚马逊国家研究所的合著者Tales Alves Jr.说。“我们的数据表明，事实远不止于此：同一种真菌似乎在周围的苔藓群落中无处不在。我们的研究结果揭示了参与操纵亚马逊蚂蚁行为的植物和真菌的生命周期之间存在着更紧密的联系。”