(译文)Carnivorous Plants

article source:nationalgeographic
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Fatal Attraction

They lure insects into death traps, then gorge on their flesh. Is that any way for a plant to behave?

作者Carl Zimmer
摄像Helene Schmitz

Largest of its kind, the South African king sundew unfurls. Leaves of this florid species can reach two feet in length.
Drosera regia


From National Geographic
Size doesn’t ensure success. If a gluey tentacle grabs too little of a big fly, the bug may suffer injury but still struggle to freedom. In the realm of carnivorous plants, says William McLaughlin, curator at the United States Botanic Garden, “some insects aren’t digested but are still victimized.”
Drosera regia

大小不能决定捕食的成功率。如果粘稠的触须只粘到了大苍蝇的一小部分,那么这只苍蝇也许会受伤,但还是能够重获自由。美国植物园园长,William McLaughlin说,在肉食类植物的王国里,“有些昆虫虽免于殉命,但难逃受伤的厄运。”

From National Geographic
Thirsty bugs are drawn to what look like dewdrops on an Australian sundew, then find themselves entangled in sticky tentacles.
Drosera stolonifera


From National Geographic
Carnivorous plants deceive, then kill. A tropical pitcher plant smells sweet to bugs, but its slippery surfaces tumble victims into its open maw.
Nepenthes lowii


From National Geographic
A Venus flytrap snaps shut if its tiny hairs are brushed twice.
Dionaea muscipula


From National Geographic
Like figures in a shadow theater, silhouettes of prey show through a Philippine pitcher plant. The waxy surface in the red tube stops bugs from climbing free. Below, enzymes leach nutrients from trapped insects.
Nepenthes alata


From National Geographic

A hungry fly darts through the pines in North Carolina. Drawn by what seems like the scent of nectar from a flowerlike patch of scarlet on the ground, the fly lands on the fleshy pad of a ruddy leaf. It takes a sip of the sweet liquid oozing from the leaf, brushing a leg against one tiny hair on its surface, then another. Suddenly the fly’s world has walls around it. The two sides of the leaf are closing against each other, spines along its edges interlocking like the teeth of a jaw trap. As the fly struggles to escape, the trap squeezes shut. Now, instead of offering sweet nectar, the leaf unleashes enzymes that eat away at the fly’s innards, gradually turning them into goo. The fly has suffered the ultimate indignity for an animal: It has been killed by a plant.

The swampy pine savanna within a 90-mile radius of Wilmington, North Carolina, is the one place on the planet where Venus flytraps are native. It is also home to a number of other species of carnivorous plants, less famous and more widespread but no less bizarre. You can find pitcher plants with leaves like champagne flutes, into which insects (and sometimes larger animals) lose themselves and die. Sundews envelop their victims in an embrace of sticky tentacles. In ponds and streams grow bladderworts, which slurp up their prey like underwater vacuum cleaners.

Most carnivorous plants eat some insects for supper but need others to help them reproduce. Some carnivorous species, such as this budding sundew, can self-pollinate if no insect emissary can be enlisted.
Drosera sp.


From National Geographic
Sensing food, a roach peers into a two-foot-tall pitcher plant. Carnivorous species photosynthesize like other plants, but most live in bogs and other nutrient-poor habitats. Enriching their diets with nitrogen captured from animals helps them thrive.
Sarracenia flava


From National Geographic
To avoid capturing and consuming prospective pollinators, pitcher plants keep their flowers far away from their traps via long stalks.
Sarracenia hybrid


From National Geographic
Blooms hang upside down like Chinese lanterns, luring bees into an elaborate pollen chamber.
Sarracenia flava


From National Geographic
A glassy cellar spider contends with the glistening tentacle tips of a South African king sundew. The more the arachnid struggles, the more likely it is to become mired in the thick mucilage globules at the ends of the tiny stalks. When the spider gives up, either from exhaustion or suffocation, it will be conveyed by the tentacle to the leaf’s center. There burning acids and enzymes will reduce its body to a nutrient soup easy for the plant to digest.
Drosera regia (sundew); Pholcus phalangioides (spider)

一只光滑的地窖蜘蛛(cellar spider)正与南非帝王毛毡苔闪闪发亮的触须展开生死搏斗。这只长脚蜘蛛越是挣扎,在厚厚的粘夜里越陷得深。当蜘蛛放弃努力,不管是精疲力竭还是窒息而亡,触须都会将它运送到叶子中心。然后强酸和酶会将它的身体变为一道营养丰富的浓汤,这样更便于植物吸收。

From National Geographic
A wolf spider treads perilously on the rim of a South American pitcher plant, perhaps looking to prey on insects drawn to the plant’s strong nectar scent. William McLaughlin, curator of the U.S. Botanic Garden, notes that spiders like this one are opportunists, often building webs directly over the mouths of pitcher plants. “It’s a great strategy,” he says, “so long as they don’t fall in themselves.”
Heliamphora nutans (pitcher plant); family Lycosidae (spider)

一只狼蛛在南非猪笼草边缘走着,这相当危险,他正在寻找被浓郁花香吸引过来的昆虫。William McLaughlin,美国植物园园长说,像这种蜘蛛,就是典型的机会主义者。他们把网直接结在猪笼草的血盆大口上。“这也是极好的方法,”他说,“只要别把自己也搭进去了。”

From National Geographic
Many of the world’s 675-plus carnivorous species set passive traps. A bun-size butterwort bristles with gluey hairs that ensnare insects until digestive juices do their work.
Pinguicula ‘Hans’


From National Geographic
A pale green butterfly senses nectar and alights on a rare California pitcher plant. Also called a cobra lily for its bulbous head, forked tongue, and long tubular pitcher, it grows in mountainous parts of the West Coast and is an oddity among its kind. Although it traps prey in a manner similar to other pitcher plants, its leaves contain no digestive enzymes. Instead, it relies on symbiotic bacteria to turn captured insects into usable nutrients.
Darlingtonia californica


From National Geographic
The thimble-size west Australian pitcher plant has a taste for insects that crawl. Its guide hairs and cloying scent encourage ants to clamber into its digestive depths.
Cephalotus follicularis


From National Geographic

There is something wonderfully unsettling about a plant that feasts on animals. Perhaps it is the way it shatters all expectation. Carl Linnaeus, the great 18th-century Swedish naturalist who devised our system for ordering life, rebelled at the idea. For Venus flytraps to actually eat insects, he declared, would go “against the order of nature as willed by God.” The plants only catch insects by accident, he reasoned, and once a hapless bug stopped struggling, the plant would surely open its leaves and let it go free.
植物以动物为食这件事十分令人震惊。这可能是因为这种行为和我们预想的常态相悖。Carl Linnaeus,18世纪伟大的瑞典自然学家,发明了生物的分类方式,在这一点上却没有始终一贯。拿捕蝇草来说,它确实捕食昆虫,Carl Linnaeus却宣称这将“违背作为上帝意志体现的自然规律。”他解释说,植物只是在偶然的情况下捕捉到昆虫,而且一旦一只倒霉的虫子停止挣扎,植物就肯定会打开叶子放走它。

Carnivorous plants lure some insects for prey but attract others for the more benign task of propagation. Heliamphora minor, which grows in the highlands of southern Venezuela, is one of the smallest pitcher plants in the world. Flower color and position signal to insects the blossom’s degree of maturity. The white color of the upside-down flower here indicates its readiness to be pollinated, while its umbrella shape protects powdery pollen from washing off in heavy rains. The burgundy bloom to its left has presumably been pollinated. The green, horizontal blossom below is still too immature to benefit from insect visitors.
Heliamphora minor

食肉植物吸引昆虫,有些是为了捕猎,有些则是为了繁衍后代。Heliamphora minor,生长在委内瑞拉南部高地上,是世界上最小猪笼草之一。花色和位置,向昆虫传递着花株成熟程度的信息。倒挂的白色花蕾表明已可以接受授粉,而伞形能够保护花粉免受暴雨侵袭。其左边酒红花蕾,可能象征着授粉完毕。和其平行的下方绿色花蕾表示尚未成熟,即便有昆虫来造访也无济于事。

From National Geographic
A water-filled North American hybrid tempts bees with the promise of nectar and a rim that looks like a prime landing pad. Carnivory is not the most efficient way for a plant to secure nutrients, but it is certainly among the most exotic.
Sarracenia hybrid


From National Geographic

Charles Darwin knew better, and the topsy-turvy ways of carnivorous plants enthralled him. In 1860, soon after he encountered his first carnivorous plant—the sundew Drosera—on an English heath, the author of Origin of Species wrote, “I care more about Drosera than the origin of all the species in the world.” He spent months running experiments on the plants. He dropped flies on their leaves and watched them slowly fold their sticky tentacles over their prey. He excited them with bits of raw meat and egg yolk. He marveled how the weight of just a human hair was enough to initiate a response. “It appears to me that hardly any more remarkable fact than this has been observed in the vegetable kingdom,” he wrote. Yet sundews ignored water drops, even those falling from a great height. To react to the false alarm of a rain shower, he reasoned, would obviously be a “great evil” to the plant. This was no accident. This was adaptation.
Charles Darwin对此了解得更为深刻,肉食性植物的种种匪夷所思的表现令他痴迷不已。他是在英国的某处荒野第一次遇见了肉食性植物——Drosera毛毡苔,没过多久,在1860年,这位《物种起源》的作者如是写到,“我对Drosera毛毡苔兴趣远胜于世上的物种起源之谜。”他花费数月时间在这些植物上做实验。他将苍蝇丢到Drosera毛毡苔的叶子上,然后观察它们粘稠的触须慢慢裹住它们的猎物。他还用少量生肉和蛋黄来刺激它们的食欲。实验发现即使只有一根头发的重量也足够Drosera毛毡苔做出反应,对此他啧啧称奇并写到“我来讲在对植物王国的观察中几乎没什么比更吸引人的了。”但是毛毡苔无视水滴的影响,即使那些水滴从高处落下,重重砸在毛毡苔上。他解释道,对雨水造成的误报做出反应,是植物的大忌。这并不是巧合。这是进化的必然结果。

Darwin expanded his studies from sundews to other species, eventually recording his observations and experiments in 1875 in a book, Insectivorous Plants. He marveled at the exquisite quickness and power of the Venus flytrap, a plant he called “one of the most wonderful in the world.” He showed that when a leaf snapped shut, it formed itself into “a temporary cup or stomach,” secreting enzymes that could dissolve the prey. He noted that a leaf took more than a week to reopen after closing and reasoned that the interlocking spines along the margin of the leaf allowed undersized insects to escape, saving the plant the expense of digesting an insufficient meal. Darwin likened the hair-trigger speed of the Venus trap’s movement—it snaps shut in about a tenth of a second—to the muscle contraction of animals. But plants don’t have muscles and nerves. So how could they react like animals?

A snail makes solemn progress up the rolled leaf of a yellow pitcher plant. Some scientists think the stalk’s squiggly vertical vein is a ladder intended to guide crawling food to the plant’s mouth. Others say it’s a structural reinforcement. Members of this skinny species can grow to three feet in height and tip over when overfilled with rainwater and the husks of prey.
Sarracenia flava (pitcher plant); family Helicidae (snail)


From National Geographic

Today biologists using 21st-century tools to study cells and DNA are beginning to understand how these plants hunt, eat, and digest—and how these bizarre adaptations arose in the first place. After years of study, Alexander Vol kov, a plant physiologist at Oakwood University in Alabama, believes he has figured out the Venus flytrap’s secret. “This,” Volkov declares, “is an electrical plant.”
当今生物学家利用21世纪的先进工具,在研究了细胞和DNA后开始逐渐了解了这些植物是如何进行捕食、消化以及它们这种古怪的特点最初是如何产生的。经过多年的研究,Oakwood大学的植物生理学家Alexander Vol kov相信他破解了捕蝇草的秘密。“这种植物,”他说,“是一株电子植物。”

When an insect brushes against a hair on the leaf of a Venus flytrap, the bending triggers a tiny electric charge. The charge builds up inside the tissue of the leaf but is not enough to stimulate the snap, which keeps the Venus flytrap from reacting to false alarms like raindrops. A moving insect, however, is likely to brush a second hair, adding enough charge to trigger the leaf to close.

Volkov’s experiments reveal that the charge travels down fluid-filled tunnels in a leaf, which opens up pores in cell membranes. Water surges from the cells on the inside of the leaf to those on the outside, causing the leaf to rapidly flip in shape from convex to concave, like a soft contact lens. As the leaves flip, they snap together, trapping an insect inside.

The bladderwort has an equally sophisticated way of setting its underwater trap. It pumps water out of tiny bladders, lowering the pressure inside. When a water flea or some other small creature swims past, it bends trigger hairs on the bladder, causing a flap to open. The low pressure sucks water in, carrying the animal along with it. In one five-hundredth of a second, the door swings shut again. The cells in the bladder then begin to pump water out again, creating a new vacuum.

Lurking half-submerged in bogs and sandbanks of the southeastern United States, the parrot pitcher plant has an appetite for arthropods, ants, and slugs. Prey are drawn to nectar inside the hood and by light shining through a latticework of “windows.” Needlelike, downward-pointing hairs line the interior, making retreat impossible—and directing prey to the plant’s acidic depths.
Sarracenia psittacina


From National Geographic

Many other species of carnivorous plants act like living flypaper, snagging animals on sticky tentacles. Pitcher plants use yet another strategy, growing long tube-shaped leaves into which insects fall. Some of the largest have pitchers up to a foot deep and can consume a whole frog or even a rat unlucky enough to fall into them. Sophisticated chemistry helps make the pitcher a death trap. Nepenthes rafflesiana, a pitcher plant that grows in jungles on Borneo, produces nectar that both lures insects and forms a slick surface on which they can’t get a grip. Insects that land on the rim of the pitcher hydroplane on the liquid and tumble in. The digestive fluid in which they fall has very different properties. Rather than being slippery, it’s gooey. If a fly tries to lift its leg up into the air to escape, the fluid holds on tenaciously, like a rubber band.
很多其他肉食性植物就像是活生生的捕蝇纸,用粘稠的触须将动物钩挂住。但猪笼草用的是另一套方法,它长出像长管一样的叶子让昆虫掉落其中。最大型的猪笼草,其叶子形成的“壶”有一英尺深,这足以消化掉在里面的青蛙或者哪只倒霉透顶的老鼠。复杂的化学特性使猪笼草成为了一个死亡陷阱。Nepenthes rafflesiana,一种长在Borneo丛林中的猪笼草会制造花蜜来诱惑昆虫,同时形成一个光滑的表面,昆虫在上面完全站不住脚。降落在猪笼草上的昆虫会在“花蜜”上失控打滑,跌落“壶”中。它们跌落在消化液里,这些消化液和“花蜜”的特性全然不同。不但一点不滑,反而相当有粘性。如果一只苍蝇试图蹬脚逃脱,这些液体会像橡皮筋一样将它牢牢箍住。

Many carnivorous plants have special glands that secrete enzymes powerful enough to penetrate the hard exoskeleton of insects so they can absorb nutrients from inside their prey. But the purple pitcher plant, which lives in bogs and infertile sandy soils in much of North America, enlists other organisms to digest its food. It is home to an intricate food web of mosquito larvae, midges, protozoans, and bacteria, many of which can survive only in this unique habitat. The animals shred the prey that fall into the pitcher, and the smaller organisms feed on the debris. Finally, the pitcher plant absorbs the nutrients released by the feeding frenzy. “Having the animals creates a processing chain that speeds up all the reactions,” says Nicholas Gotelli of the University of Vermont. “And then the plant dumps oxygen back into the pitcher for the insects. It’s a tight feedback loop.”
很多肉食性植物都有特殊的腺体以分泌酶,而这些酶相当强大,足以穿透昆虫坚硬的外壳,这样它们就能吸收猎物体内的营养了。但是紫猪笼草会利用其它微生物来帮助它消化食物,它们大多生活在北美沼泽地区和贫瘠沙地。这里有着复杂的食物链,蚊子幼虫,蠓,单细胞生物和细菌,它们很多只能在这个特殊的栖息地生存。动物将它们的猎物撕碎后会有残渣掉进猪笼草,于是微生物开始食用这些残渣。它们疯狂进食时产生的营养素最终被猪笼草所吸收。“通过动物的参与,这条生态链的转化速度大大加快,”Vermont大学的Nicholas Gotelli说。“然后植物将氧气返还给猪笼草中的昆虫,这是一个相当紧凑的循环。”(译者注:这个生物链循环的逻辑没怎么读懂,氧气返还给猪笼草中的昆虫也算是个循环吗?不给不是更好?)

Pitcher plants grow by the thousands in the bogs at the Harvard Forest in central Massachusetts. One late spring day Aaron Ellison took me on a tour, stopping from time to time to watch patiently as I pulled a sinking leg out of the muck. “You haven’t had a real bog experience till you’re up to your crotch in it,” said Ellison, a senior ecologist at the forest. Little orange flags fluttered across the bogs. Each one marked a pitcher plant impressed into the service of science. In the distance a student was feeding flies to the flagged plants. The researchers raise these insects on food spiked with unusual forms of carbon and nitrogen so they can later harvest the pitcher plants and measure how much of each element from the flies has been absorbed into the plants. Because pitcher plants grow slowly (they can live for decades), the experiments can take years to yield results.
在Massachusetts中部Harvard森林的沼泽中生长着数以千计的猪笼草类植物。春末的某天,Aron Ellison——这片森林中资深的生态学家,带我游览了一番,他不时停下脚步耐心观察地形,而我却频频陷入烂泥之中,举步维艰。“如果你没有过大半个身子陷入泥沼的经历,就谈不上对沼泽有什么真切地体会了,”Ellison说到。沼泽地里飘动着一面面桔黄色的小旗。每个都标记了一株供科学研究用的猪笼草。不远处的一个学生正在用苍蝇喂食这其中的一株。研究人员用添加了特别碳、氮成分的食物来喂养这些昆虫,这样他们就能从随后收集到的猪笼草里测出每种成分被植物吸收了多少。因为猪笼草生长缓慢(它们可以存活数十年),这项实验可能要花数年才能得出结果。

Ellison and Gotelli are trying to figure out what evolutionary forces pushed these plants toward a taste for meat. Carnivorous plants clearly benefit from eating animals; when the scientists feed pitcher plants extra bugs, the plants get bigger. But the benefits of eating flesh are not the ones you might expect. Carnivorous animals like ourselves use the carbon in protein and the fat in meat to build muscles and store energy. Carnivorous plants instead draw nitrogen, phosphorus, and other critical nutrients from their prey in order to build light-harvesting enzymes. Eating animals, in other words, lets carnivorous plants do what all plants do: grow by grabbing energy directly from the sun.

Alas, they do a lousy job of it. Carnivorous plants turn out to be very inefficient at converting sunlight into tissue. That’s because they have to use a lot of energy to make the equipment they need to catch animals—the enzymes, the pumps, the sticky tentacles, and so on. A pitcher or a flytrap cannot carry out much photosynthesis because, unlike plants with ordinary leaves, they do not have flat solar panels that can grab lots of sunlight. Ellison and Gotelli suspect that only under special conditions do the benefits of carnivory outweigh the costs. The poor soil of bogs, for example, offers little nitrogen and phosphorus, so carnivorous plants enjoy an advantage there over plants that obtain these nutrients by more conventional means. Bogs are also flooded with sunshine, so even an inefficient carnivorous plant can carry out enough photosynthesis to survive. “They’re stuck, and they’re making the best of it,” says Ellison.

Evolution has repeatedly made this trade-off. By comparing the DNA of carnivorous plants with other species, scientists have found that they evolved independently on at least six separate occasions. Some carnivorous plants that look nearly identical turn out to be distantly related. Both kinds of pitcher plants—the tropical genus Nepenthes and the North American Sarracenia—grow deep pitcher-shaped leaves and employ the same strategy for capturing prey. Yet they evolved from different ancestors.

A cave cricket is caught in the sticky clutches of a king sundew.
Drosera regia (sundew); family Gryllacrididae (cricket)


From National Geographic
The trapped insect struggles to free itself.
Drosera regia (sundew); family Gryllacrididae (cricket)


From National Geographic
Possibly injured but certainly fortunate, the cricket plummets to freedom. “Whether a bug will get away or not is a mortal battle decided in moments,” says Barry Rice, a botanist at the University of California, Davis.
Drosera regia (sundew); family Gryllacrididae (cricket)
From National Geographic

In several cases scientists can see how complex carnivorous plants evolved from simpler ones. Venus flytraps, for example, share an ancestor with Portuguese sundews, which only make passive flypaper glands on their stems. They share a more recent ancestor with Drosera sundews, which not only make flypaper glands but can also curl their leaves over their prey. Venus flytraps appear to have evolved an even more elaborate version of this kind of trap, complete with jawlike leaves.

Unfortunately, the adaptations that enable carnivorous plants to thrive in marginal habitats also make them exquisitely sensitive to environmental changes. Agricultural runoff and pollution from power plants are adding extra nitrogen to many bogs in North America. Carnivorous plants are so finely tuned to low levels of nitrogen that this extra fertilizer is overloading their systems. “They eventually burn themselves out,” says Ellison.

Humans also threaten carnivorous plants in other ways. The black market trade in exotic carnivorous plants is so vigorous now that botanists are keeping the location of some rare species a secret. Venus flytraps are being poached from North Carolina by the thousands to be sold at roadside stands. The North Carolina Department of Agriculture has been dabbing wild Venus flytraps with harmless dye that’s normally invisible but glows in UV light so that inspectors who come across Venus flytraps for sale can quickly determine if the plants were raised in a greenhouse or poached from the wild. But even if the poaching of carnivorous plants can be halted (a very big if), they will continue to suffer from other assaults. Their habitat is disappearing, to be replaced by shopping centers and houses. Fires are being suppressed, allowing other plants to grow quickly and outcompete the Venus flytraps. Good news, perhaps, for flies. But a loss for all who delight in the sheer inventiveness of evolution.

Most famous and fascinating of all carnivorous plants, the Venus flytrap uses electricity to capture unsuspecting prey. When one or more of its surface hairs are brushed twice—an energy-conserving system that distinguishes prey from other stimuli—an electrical charge signals cells on the outside of the leaf to expand, swiftly warping the shape of the plant’s thumbprint-size lobes from convex to concave and snapping them shut. The hairlike spikes on the end of the lobes, called cilia, then mesh together inexactly, letting small prey escape but trapping prizes large enough to be worth digesting.
Dionaea muscipula


From National Geographic

p.s1: 图床在Picasa,已彻底被墙,请自备翻墙工具或参见原文或纯文字阅读。

p.s2: 无责任翻译,文章译后也只审过一遍。有异议者请参见原文,用自己的智商理解,勿盲信。

p.s3: 这是3月份那期里的文章,因为一直被有些事搁着,所以始终没能动笔。得到的教训是:时间宝贵,做什么都拖拉不得。

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