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本·丹汉姆

更新时间:2017-05-11

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海洋国际都市,森林城市:生态,多样化和文化

BBC系列纪录片《地球脉动第二季》(Planet Earth II)第六集名为《城市》,它讲述了生存在世界各地城市中心的动物们的生活。我们可以看到人类文明和其他动物文明的诸多碰撞,而这些动物或是面临致命结果,或是成功地适应城市环境。虽然通常是其他动物被迫适应我们人类构建的环境,但《城市》在结尾描述了一个振奋人心的愿景:我们可以通过建设高密度城市,为比城市中现有的更大的物种多样性提供栖息地,从而实现对环境的适应。

对有着强烈浪漫主义情感的人来说,这种构建的生态系统的愿景可能会令其十分困扰。但我认为文献和生物科学都可以为我们提供深刻见解,它们可以帮助我们走出关于自然的浪漫想法,并探索曾有着深不可测的深度或难以穿越的荒野的海洋都市或森林城市。

秘鲁作家塞萨尔·卡尔沃(César Calvo)在其1981年首次出版的小说《InoMoxo的三个搭档和亚马孙河的其他巫医们》(Las Tres Mitades de Ino Moxo y otros Brujos de la Amazonía)中,描述了故事讲述者塞萨尔·索里亚诺(César Soriano)和巫医们的一系列邂逅,这些巫医都和传奇的隐士Ino Moxo(即小说的中心人物)有一定的联系。这些邂逅是索里亚诺穿越亚马孙之旅的一部分,并最终带他见到了Ino Moxo。卡尔沃的这部小说明确地表达了亚马孙世界观的方方面面——一种“深奥文化”——它们或能帮助我们从批判思维和现代生物科学的角度对生态进行全新的理解。

我想通过对海居蓝藻细菌 “原绿球藻”的生态描述,引入对卡尔沃小说的阐述。海洋生物学家萨莉·奇泽姆(Sallie Chisholm)是“原绿球藻”研究领域的先驱。此处的想法是建立一种生态批判思维,这种思维不考虑浪漫主义和自然文学的传统,并重视充分考虑二十一世纪微生物科学的细节问题。我的侧重点是微生物,因为我认为我们能得出这样一个合理的论证,即生态系统中发挥作用的、最不可或缺的有机体是微生物。更广泛地讲,所有的多细胞生物都是微生物生态学的产物。微生物还为我们提供了方法,以细致地研究构成生态互联性之网的有机体间的密切联系。

一直以来,“生态(ecology)”一词在人文学科领域的使用都是宽泛而含糊,为摆脱这一局面,我们需要查看其来源的具体的生态和有机体。就这一点而言,“原绿球藻”十分有用,因为它可被视为“阐述塑造微生物人口和生态系统之力量的模型系统”。我对塞萨尔·卡尔沃的小说的讨论建立在这一观点的基础之上,即小说——特别是英美和欧洲传统之外的那些作品——能够为我们在复杂生态中设想自己的位置提供新的方法,且这些设想方法能和对生态过程的、以科学为基础的理解联系起来。

卡尔沃小说中的关键场景(就我们这个简单讨论而言)是故事讲述者塞萨尔·索里亚诺和唐·哈维尔的邂逅,地点是位于秘鲁西亚马孙地区普卡尔帕Tariri酒店的酒吧。唐·哈维尔是一位巫医,在死藤水的使用上经验丰富。死藤水是亚马孙地区用来产生幻觉或作为一种亚马孙植物医学学科。在这次交流中,唐·哈维尔告诉索里亚诺:

“地球由从未被披露的美构成,或是由被广泛披露的美构成,这点更糟糕。我来举个例子,你应该已经看到Tariri酒店墙上的那些画了。”

这些画的设计由希皮博人完成,他们是史前时期诸多亚马孙民族中的一个,但此时酒店墙上的画只是复制,并没有考虑其重要涵义。随后,唐·哈维尔向索里亚诺解释了自己是如何理解希皮博人的设计的。他说道,这些在我们看来可能仅仅是好看的图画,实际上是灵魂的肖像。

“要知道,有一根无形的绳子,你可能才开始看到、学习到,且通过普通肉身之眼是看不到的。我已经看过了这面画壁,但实际上我并不是在看这样一面画壁。很明显,它是人的灵魂的模样!”

索里亚诺回应道:

“线型的肖像,”我自言自语道,“它们看起来就像城市地图。”

“就是这样!”他的声音激动了起来,“对的!就是线型的肖像!并不是说它们看起来像城市地图,而是它们本就是!没错,灵魂就是移动的城市!希皮博人的画就是地图,只不过是森林城市的地图,有不可思议的河流横贯其中,而不是街道,有迂回的曲径迷宫贯穿其中,而不是严格管制的道路,有深谷、阴郁和沼泽做点缀,而不是冰冷的公园、电影院和林荫大道!城市地图,不是灵魂的肖像!位置变动了的房屋,就像丛林中的生活,就像阿萨宁卡族人的房屋,他们每年都要迁徙,烧掉自己的小屋和花园,让一切归于混沌,然后去到其他的地方,再开始建造庇护之所,播种、撒下生活的种子,随后下一年又将一切焚毁,再去到别处重生!和我们一经诞生即知道自己的未来、且受惰性和惯性束缚的城市不同,它们已掌握了自己的日子将会如何以及在前方等着它们的房屋和街道!我们的城市生来就是死的,就像是小树的那些枝干,早在成熟前已满是蠕虫。”

我正是想将对森林城市的此类愿景——及可在希皮博艺术品中找到的它的基底结构地图——和已知的“原绿球藻”信息联系在一起。此处,我将从标题为《原绿球藻:集体多样性的结构与功能》(Prochlorococcus: the structure and function of collective diversity)的文章出发。我想对二者做一个类比:森林城市之前被隐藏的、但可从唐·哈维尔所述之希皮博艺术品中显现的结构,和被视为海洋生态之地图的、隐藏的,但通过对“原绿球藻”的了解(其分布、多样性和与其他有机体的相互作用)可知的微生物多样性的结构。

萨莉·奇泽姆将“原绿球藻”及其他进行光合作用、并生产出地球50%的大气氧气含量的微生物称为海洋的“隐形森林”。“原绿球藻”是“地球上最小且最丰富的光合作用有机体”。然而,尽管数量十分可观,但由于体型微小,直到1985年它们才被发现。据估计,该属内的微生物产出了大气中20%的氧气。“原绿球藻”固定的碳含量大约相当于全球农作物的净生产率。显然,这一有机体在全球气体和养分循环中发挥着重要作用。

单个的“原绿球藻”细胞不仅个头微小,还有很小的基因组,有些分离菌只有1700个基因。这是目前已知的所有从日照中获取能量的有机体中基因组最少的,比人类基因组要少约12倍。但这并不是全部,如果估算已经适应了不同海洋生态位的“原绿球藻”的各类菌株上的基因总数,我们会得到一个数字,大致为84000个基因。这个泛基因组约是人类基因组的四倍。

文章的副标题,“集体多样性的结构与功能(the structure and function of collective diversity)”,正是我得出这些数字的来源,它表明考虑“原绿球藻”的泛基因组(即不同菌株所有基因的总和)是很有道理的,因为这种集体多样性是有机体在变化的生态中成功存活的关键。但由于病毒基因可在菌株间移动,以至于萨莉·奇泽姆指出一提到“原绿球藻”,人们可能就会想象海洋中居住着拥有分解的基因信息的生物,那么这样考虑也是说得通的。

稍后我们再看来看这部分的描述,但首先我想概述下推动“原绿球藻”基因多样性的一些动力。从最宽泛的水平看,菌株可分为适应高光照强度和低光照强度的种类。低光照强度的菌株能在比其他任何光合有机体都深的深度,进行光合作用,在海平面以下约200米的位置。低光照强度的菌株中有更大的基因多样性。关于这点,有一个解释是:受天气和波浪影响,表层水不断地被混合,就养分和温度而言,生成了一个相对比较同质化的环境。但是,越来越深地朝着海底探索时,我们发现光照、温度、压力和养分都有了稳定的梯度。正是这些梯度的稳定性,使“原绿球藻”菌株的多样化成为了可能,这些菌株在水体的不同梯度中占据着具体位置。

此时,我们开始稍稍了解我称为“原绿球藻”海洋国际都市的概念。深海中的稳定梯度是构成这一生物的多样性的城市结构的动脉路径。追踪这些路径,我们就能够创建这些微生物城市的地图。

这一结构多样性中的另一个因素是病毒的角色,它们既可以作为产生新的耐药菌株的进化压力,也可以成为菌株间遗传信息的载体。基因以传病媒介在菌株间运动是运动中的微生物城市的动力的一部分。在海洋的任意指定深度,我们还在构成成型群落的“原绿球藻”细胞中发现了微观多样性。甚至是在通常被认为是单个菌株的克隆体中,也发现了基因层面的多样性。宏观和微观层面的多样性都给“原绿球藻”提供了遗传信息库,从而快速适应所处环境的变化。毫无疑问,这对它作为有机体的成功一直是十分重要的。

此处我一直在讨论的文章的几位作者认为,“原绿球藻”可被视为“多种细胞的联合”:

“诸多生物群的大合集,每一个都展现了对特定环境变量的适应并代表了反映重大生态位维度的等位基因(基因的变体形式)的组合配置。”

“原绿球藻”是一个典型群落,能够帮助我们在实际生态环境中为生态批评建立牢固理论基础的诸多群落之一。尽管没有详细地探索“原绿球藻”和其他有机体(包括助其生长的其他细菌)的关系,我们希望可以开始欣赏“原绿球藻”海洋国际都市的卓越结构。

通过文献和生物科学,从而学着去感知之前隐形的结构——森林城市或海洋国际都市,这样可以将我们和构成我们的世界的非人类文明带入到更为亲密的伦理关系。我认为保护、研究和学着去感知之前隐形的当下非人类城市(虽然只是通过生物学和文献),每一点看起来都和建造高密度的、可支撑最大可能的生活多样性的人类城市同等重要,并想要通过这个观点的提出回到我一开始提到的《地球脉动第二季》第六集上。

参考文献

Steven J. Biller et. Al. ‘Prochlorococcus: the structure and function of collective diversity’, Nature Reviews Microbiology, volume 13, issue 1, January 2015.

César Calvo, Las Tres Mitades de Ino Moxo y otros Brujos de la Amazonía, Proceso Editores y Editorial Gráfica LABOR,1981.

Sallie Chisholm, Invisible Forest: Microbes of the Sea, MIT TechTV, online video, recorded 15 November 2006, accessed 4 April 2017.

Sallie Chisholm, Carl Zimmer, ‘Harvesting the Sun’, Meet the Scientist, Episode 41, 6 January 2010, accessed 4 April 2017.

Ocean Cosmopolis, Forest City: ecology, diversity, culture

Ben Denham

‘Cities’, episode six of the BBC documentary series Planet Earth II, looks at the lives of animals living in urban centres all over the world. We see a variety of encounters between human and other animal cultures; sometimes with deadly consequences for the other animals and sometimes stories of successful animal adaptation to the urban environment. While it is generally the other animals that are being forced to adapt to our built environments ‘Cities’ ends with a stirring vision of how we might adapt by building high density cities that that are designed to provide habitat for a far greater diversity of species than those that currently live in our cities. 

This vision of a constructed ecosystem may be troubling to those of us with strong Romantic sensibilities but I’d like to argue that both literature and the biological sciences can offer us insights that might help us to move beyond romantic ideas about nature and see an ocean cosmopolis or a forest city where once we saw unfathomable depths or impenetrable wilderness.

In his novel Las Tres Mitades de Ino Moxo y otros Brujos de la Amazonía (The Three Halves of Ino Moxo and other Witch Doctors of the Amazon), first published in 1981, Peruvian author César Calvo describes a series of encounters between his narrator, César Soriano, and witch doctors who all have some association with Ino Moxo, the figure at the centre of the novel. These encounters are part of a journey through the Amazon that leads to César Soriano’s meeting with Ino Moxo. Calvo’s novel articulates aspects of an Amazonian cosmovision — a kind of deep culture — that might help us to come to new understandings of ecology in relation to critical thought and the contemporary biological sciences. 

I want to bring Calvo’s novel into conversation with an ecological account of the ocean dwelling cyanobacteria Prochlorococcus whose study was pioneered by biological oceanographer Sallie Chisholm. The idea here is to model a kind of eco-critical thought that bypasses the Romantic and nature writing traditions and takes seriously the problem of thinking through the details twenty-first century microbial science. I’m focusing on microbes because I think we can make a reasonable argument that the most indispensable organisms in ecosystem functioning are microbial. More broadly all multicellular life is the product of microbial ecologies. Microbes also provide us with the means to study in detail the close associations between organisms that weave the webs of ecological interconnectedness. 

To move beyond a general and vague sense of how the term ecology has been used in the humanities we need to look at specific ecologies and the organisms that produce them. Prochlorococcus is useful in this regard because it can be thought of as a ‘model system for elucidating the forces that shape microbial populations and ecosystems’. My discussion of César Calvo’s novel is premised on the idea that fiction — particularly from beyond the Anglo and European traditions — can give us new ways of imagining our place in complex ecologies, ways of imagining that can be related to science-based understandings of ecological processes. 

The key scene from Calvo’s novel — for the purposes of this brief discussion — is an encounter between the narrator César Soriano and Don Javier, in the bar of the Hotel Tariri, Pucallpa, a city in the western Amazon region of Peru. Don Javier is a witch doctor who is experienced in the use of ayahuasca; a psychedelic brew that is used in the Amazon for both the visionary experiences it provides and as part of the discipline of Amazonian plant medicine. During this encounter Don Javier tells the narrator that: 

This earth is made of beauties that have never been told, or that has been told badly, which is worse. I’ll give you an example; you’ve seen those drawings on the walls of Hotel Tariri.

The design of these drawings was produced by the Shipibo people — one of the many prehispanic Amazonian nations — but here on the walls of the Hotel it has been copied without regard to its significance. Don Javier then explains to César Soriano how he understands the Shipibo designs. He tells Soriano that what might appear to us to be merely pretty pictures are actually portraits of souls. 

There’s an invisible thread, you know, that you might start to see, that you learn, and that you don’t see with the eyes of your material body. I’ve looked at this painted wall and in reality I’m not looking at a painted wall. There, clearly, is the face of a man’s soul! 

Soriano responds:

Linear portraits, I said to myself, they look like maps of cities.

Exactly! his voice excited. That’s right linear portraits! It’s not that they look like maps of cities, that’s what they are! Yes, souls are cities in movement! The Shipibo drawings are maps, but of forest cities, cut through with impossible rivers, not avenues, labyrinths of winding paths, not regimented streets, lovers, ravines, sadness and swamps instead of cold parks, cinemas and boulevards! Maps of cities, rather than portraits of souls! Houses that change place, just like the days of life in the jungle, just like the houses of the Ashaninka who move every year and burn their huts and their gardens and return everything to the tangle, and go somewhere else and start again building their shelter, sowing their seeds, their life, before burning it all again the following year and going elsewhere to be reborn! Not like our cities that are born and already know their future, chained to rust and habit, they already know how their days will be and the houses and streets that await them! Our cities are born dead, they look like those skeletons of young trees, full of worms before they mature.

It is this vision of the forest city — and the maps of its underlying structure that we might find in the Shipibo artwork — that I’d like to relate to what we know about Prochlorococcus. Here I’m working from a review titled ‘Prochlorococcus: the structure and function of collective diversity’. I’d like to draw an analogy between the previously hidden structures of the forest city, that can emerge from the Shipibo artwork that Don Javier describes, and the hidden structures of microbial diversity — what we might think of as maps of ocean ecologies — that emerge through our knowledge of Prochlorococcus, its distribution, diversity, and interactions with other organisms.

Sallie Chisholm has called Prochlorococcus and the other photosynthetic microbes that produce 50% of the planet’s atmospheric oxygen the ‘invisible forests’ of the ocean. Prochlorococcus is ‘the smallest and most abundant photosynthetic organism on Earth’. Despite its abundance and because of its diminutive size it was only discovered in 1985. It is estimated that this genus produces 20% of the oxygen in our atmosphere. The amount of carbon fixed by Prochlorococcus is roughly equivalent to the net global productivity of our agricultural crops. Clearly this organism plays a major role in global gas and nutrient cycles. 

Individual Prochlorococcus cells are both physically small and have small genomes, with some isolates having only 1 700 genes. From what is known this is the smallest genome of all organisms that get their energy from the sunlight. It is about 12 times smaller than the human genome. But this is only part of the story. If we estimate the total number of genes from all the various strains of Prochlorococcus that have adapted to different niches in our oceans we come to a figure of roughly 84 000 genes. This pan-genome is about 4 times the size of the human genome. 

The subtitle of the review that I’m getting these numbers from — ‘the structure and function of collective diversity’ — suggests that it makes sense to think about the Prochlorococcus pan-genome — that is, the sum of all genes across different strains — because this collective diversity is central to the success of the organism in varying ecologies. But it also makes sense to think this way because viruses move can genes between strains in a way that has led Sallie Chisholm to suggest that when it comes to Prochlorococcus we might think of the ocean as being populated by dissolved genetic information. 

We’ll come back to this description in a moment but first I want to outline some of the forces driving genetic diversity in Prochlorococcus. At the broadest level strains are categorised into those that are adapted to high and low light levels. The low light strains can photosynthesise at greater depths than any other photosynthetic organism; down to about 200m below the ocean surface.  There is greater genetic diversity among low light adapted strains. One explanation for this is that surface waters are constantly being mixed by weather and waves leading to a relatively homogenous environment in relation to both nutrients and temperature. However, as we go deeper into the ocean we find stable gradients of light, temperature, pressure, and nutrients. It is the stability of these gradients that allow for the diversification of the Prochlorococcus strains that occupy specific places along these various gradients in the water column. 

Here we start to get a hint of what I’m calling the Prochlorococcus ocean cosmopolis. The stable gradients of the deeper ocean are the arterial paths that make up the cosmopolitan structure of this organism’s diversity. Tracing these paths will allow us to create maps of these microbial cities. 

Another factor in this structure diversity is the role of viruses as both an evolutionary pressure that produces new resistant strains and as carriers of genetic information between strains. This movement of genes between strains on viral vectors is part of the dynamics a microbial city in movement. At any given depth in the ocean we also find microdiversity in the Prochlorococcus cells that make up stable communities. Even among what would generally be considered clones of a single strain of we find diversity at a genetic level. Diversity at both the macro and micro levels gives Prochlorococcus the genetic repertoire to adapt quickly to changes in its environment and has undoubtedly been important to its success as an organism. 

The authors of the review that I’ve been discussing here suggest that Prochlorococcus can be viewed as ‘a federation of diverse cells’:

a large collections of many groups, each of which exhibits different adaptations to specific environmental variables and represents combinatorial arrangements of alleles [variant forms of a gene] that reflect important niche dimensions. 

Prochlorococcus is a model community, one of many that might help us to ground ecocriticism more firmly in actual ecologies. Even without going into the detail of the relationships between Prochlorococcus and other organisms — including the other bacteria that help its growth — we can hopefully start to appreciate the remarkable structure of the Prochlorococcus ocean cosmopolis.

Thinking through literature and the biological sciences to learn to perceive previously invisible structures — a forest city or an ocean cosmopolis — can bring us into more intimate and ethical relationships with the non-human cultures that structure our world. To return to the episode of Planet Earth II that I began with I’d like to end by suggesting that protecting, studying, and learning to perceive the previously invisible non-human cities of the present — though biology and literature — seems every bit as important as building high density human cities that can support the greatest possible diversity of life.

References

Steven J. Biller et. Al. ‘Prochlorococcus: the structure and function of collective diversity’, Nature Reviews Microbiology, volume 13, issue 1, January 2015.

César Calvo, Las Tres Mitades de Ino Moxo y otros Brujos de la Amazonía, Proceso Editores y Editorial Gráfica LABOR, 1981.

Sallie Chisholm, Invisible Forest: Microbes of the Sea, MIT TechTV, online video, recorded 15 November 2006, accessed 4 April 2017. 

Sallie Chisholm, Carl Zimmer, ‘Harvesting the Sun’, Meet the Scientist, Episode 41, 6 January 2010, accessed 4 April 2017.