JOIN USFloral flouters of the food chain
As a refined Victorian gentleman, Charles Darwin naturally gravitated toward the macabre, and few things fascinated him like those floral flouters of the conventional food chain: carnivorous plants. He experimented with them and wrote a major treatise. He called the Venus flytrap, with its elaborate hair-trigger snap trap and its lethal brew of digestive juices, “one of the most wonderful plants in the world.” He compared the glistening and gothically tentacled sundew plant, or Drosera, to a “most sagacious animal” and said, “I will stick up for Drosera to the day of my death.” To which a sagacious sundew might well have replied, Thanks, but I’ll take a damselfly instead.
As a bounty of new research reveals, biologists are still sticking up for carnivorous plants, and still unearthing surprising details about the anatomy, evolution, biochemistry and hunting tactics of what Rainer Hedrich of the University of Wurzburg calls “the green flesh-eaters.” One team lately has determined that a pitcher plant in Borneo supplements its insectivorous diet with regular helpings of bat guano, attracting the bats to roost, and void, in its slender goblet of a modified leaf by tuning its shape to precisely match the bats’ echolocating calls. Another team has nearly decoded the complete DNA sequence of the Venus flytrap, which is virtually the same size as the human genome, and has seen hints that, at some point in its evolutionary history, the plant may have imported from its insect prey nerve-related genes that in turn allowed the plant’s trapping mechanism to shut faster.
Other researchers have compared proteins and hormones found in the digestive fluids of carnivorous plants with similar molecules active in noncarnivorous plants and concluded that a good offence was born of a good defence. Carnivorous plants, the researchers argue, gained the power to pulverise and absorb their insect prey by repurposing the defensive chemicals that ordinary plants use to deter herbivorous insects, effectively pounding shields into swords.
Social & viral
Or maybe selfie sticks. Paulo Minatel Gonella of the University of Sao Paulo in Brazil and his colleagues recently reported in the journal Phytotaxa that they had identified a spectacular new species of sundew with the help of social media. After seeing photographs of the plant posted by an amateur naturalist on Facebook, the researchers travelled to the specified location, on a lone mountain in southeastern Brazil, and confirmed the sundew was new to science. With stems reaching five feet long, Drosera magnifica practically qualifies for a turn on “Little Shop of Horrors” and is the largest sundew species in the Americas. With the bulk of its rosy, sticky tentacles enfolding trapped prey, the sundew stalks resemble nothing so much as giant insect kebabs.
Yet while D. magnifica’s image has gone viral, researchers warn the real thing may soon go extinct, its habitat threatened by coffee and eucalyptus plantations. Researchers see in carnivorous plants a model for exploring a range of important questions, including how organisms adapt to extreme adversity and scarcity, and how sessile beings with neither muscles nor brains can outmanoeuvre mobile beings with both. Carnivorous plants may yield practical spinoffs, too. Rainer pointed out that a number of enzymes in carnivorous plants remained exceptionally stable under conditions of high heat and blistering acidity that demolished most garden-variety enzymes.
The kinkiness of their meat-eating aside, the 590 or so known species of carnivorous plants are all legitimate, chlorophyll-carrying members of the kingdom Plantae. They photosynthesise, as other plants do, stitching together sugars from water, carbon dioxide and sunlight. Yet plants also need nutrients like nitrogen, phosphate and sulfur, which most species absorb from the ground. Carnivorous types, however, colonise marginal habitats with impoverished soil and must acquire their nutrients from alternative sources. Carnivorous plants thrive in open bogs; in damp, fireswept sand; by roadside puddles; in the leached mud of a mountainside — bright, sodden spots where competitors are negligible, the insects gullible, and nutrients alone limit plant growth.
Through DNA analysis, researchers recently determined that carnivory has arisen in plants at least nine times, the oldest lineage dating back some 72 million years. Participants have evolved a battery of techniques for trapping and digesting their quarry, which generally means insects and other arthropods but can include frogs, fish and even small mammals.
‘First action potential’
Others exude sticky droplets, or operate like a lobster trap, with spiralling grooves and pointing hairs that usher the prey through a nested set of ever-narrowing barriers and into the digestive centre. Perhaps the most impressive snare belongs to the rightfully legendary Venus flytrap, which can still be found in a scattering of swamps in the Southeast. Rainer, a biophysicist who studies the plant as a kind of “serious hobby,” and his colleagues have determined that the trap, a highly modified leaf, relies on an action potential, or electrical pulse, to snap shut, a rare power in the floral community.
When a Venus flytrap is hungry, its two-lobed trap, now flushed with attractive red pigment, opens and exposes the plant’s sensory hairs. Should an insect land and jostle a hair, Rainer said, “that triggers the first action potential.” And if, in the next 30 seconds, the luckless visitor touches another hair, wham, the trap snaps shut in tenth of a second — three times faster than a blink of an eye. Naturally, the insect struggles to escape, Rainer said, “but this is just more bad news.” The desperate motions provoke more action potentials, stimulating the plant to flood its trap with hydrochloric acid, pepsin-and trypsin-class enzymes, and chitinase to pierce through the insect’s exoskeleton and liquefy its meat. The green mouth becomes the green stomach becomes the green intestine, Rainer said, and within seven to 10 days, prey and predator are as one.