The Insane Biology of: The Venus Flytrap

Here’s a sanitized version of the provided YouTube transcript:

—

In 1875, Charles Darwin published a book that would go on to shake the scientific community to its core. Some even claimed that what he published was impossible and against the order of nature. His observations began with a peculiar plant in the south of England. He noticed dozens of dead insects, or what remained of them, adhered to the sticky tentacles of the common sundew plant.

Many plants cause the incidental death of certain insects; for example, the horse chestnut regularly kills insects that get stuck to its protective sticky film. But Darwin had a hunch that these insect deaths were no accident. He collected specimens and began extensive experimentation to find out if these plants could really be catching insects on purpose to trap them in order to eat them. He fed his plants salts of ammonia, egg white, various insects, and even small chunks of cheese. Soon, he was able to scientifically describe their digestive systems and prove unequivocally that plants can indeed eat meat.

Today, there are over 600 species of carnivorous plants known to science. Darwin’s beloved sundew plant is in the adhesive trap category, where prey becomes stuck to extremely sticky droplets. Then there are the pitfall traps, like pitcher plants, where prey falls into the base and is digested. There’s also the suction traps, like the water wheel plant, where aquatic prey gets sucked into a one-way trapdoor. But the most iconic of all carnivorous plants are the snap traps, like the Venus flytrap.

Unsuspecting prey, lured by the flytrap’s sweet-smelling nectar, land in the jaws of the flytrap and quickly find themselves locked behind the teeth of the hungry plant, where they are digested slowly over the course of a week. The discovery of these meat-eating plants changed the very idea of what it means to be a carnivore. But how and why would plants evolve such a taste for flesh?

Venus flytraps are naturally found in only one area in the world: the coastal plains of North and South Carolina, specifically in one small region 200 kilometers across. They are small plants that live in the open understory of their habitat, which remains open due to natural fires that burn away the larger shading plants.

The trap of the Venus flytrap is a leaf with two lobes connected at a hinge on its stalk. The lobes sit waiting, curved in the open position, luring prey insects with sweet-smelling nectar. If something like a fly, spider, or beetle lands on or crawls across the gaping jaws, it risks touching any of the flytrap’s six sensory hairs. If it touches a single hair, the plant won’t budge, and the insect is safe for now. However, a crucial 30 seconds begins within the plant that will determine if the insect lives or dies.

If the insect touches another sensory hair within the 30-second window, the insect is doomed. Upon the second touch, the lobes snap shut faster than the blink of an eye. The plant’s movement is controlled by an electrical signal created by the hairs. When a hair is bent by touch, it acts as a lever that stretches the envelopes of cell membranes at its base. The stretching causes ion channels to burst open, allowing positively charged calcium ions to flood out, creating an action potential, or electrical signal, that spreads from the hair over the entire trap. After two action potentials, the trap snaps shut.

The reason it needs two triggers within a 30-second window is to prevent the plant from closing erroneously and wasting energy on something like a raindrop or a twig. Researchers had a hunch that it had to do with changes in calcium concentrations inside the leaves. To test this, they genetically modified Venus flytraps to emit green fluorescence when calcium ions were present in the leaf cells. When the first hair is touched, a flood of green overtakes the leaf, indicating a high presence of calcium ions. As the seconds pass, the concentration slowly starts to drop. If a second hair is touched, the calcium concentration again increases, flooding the leaf with even more green.

It’s only when a certain threshold is reached in the calcium concentration that the trap snaps shut. This threshold can only be reached if the two stimuli occur within 30 seconds. However, the timed triggers are not the only way a Venus flytrap ensures it eats only the things it wants. If you have a pet Venus flytrap, you may realize you can trigger two hairs yourself, causing it to snap shut. This may tempt you to feed it cheese, like Darwin did with his sundew plants. But if you did, you’d end up disappointed.

You could indeed get the flytrap to close on the cheese initially, but after a few hours, it will reopen, rejecting your generous gift. That’s because the plant requires sustained wiggling within its jaws to fully seal and begin the digestive process. This ensures it’s using its digestive resources only on hearty insect meals. Once a wriggling bug causes the trap to fully seal, it’s no longer a mouth but a stomach. Digestive juices flood into the closed trap, the pH drops dramatically, and meat-digesting enzymes similar to those in our stomachs start to break down the trapped creature.

Slowly, over the course of a week or so, the insect’s body is liquefied, and the lining of the trap absorbs the nutrients. It’s an impressive, if unsettling, survival strategy. It’s hard to look at this small plant and understand how it came to be. How do plants make the jump from getting all their nutrients from the soil and the sun to luring and killing living creatures?

While the Venus flytrap does extract some energy from its food, what it’s really after when it kills prey is nitrogen. Plants need nitrogen to successfully carry out photosynthesis, as it’s a major component of chlorophyll. It’s also a major component of amino acids, the building blocks of proteins, and is needed for general growth and regeneration in the plant. Without nitrogen, a plant will wither and die.

This could be a major problem for plants growing where the Venus flytrap does. The particular area of the Carolinas where they live has soil that is extremely acidic and nitrogen deficient. But this lack of nutrients is no problem for the Venus flytrap, which gets between 50 and 75% of its nitrogen from consuming insects. A similar story is true for other carnivorous plants.

Carnivory evolved in plants to cope with nutrient-scarce soils. That explains the “why,” but how does a plant evolve from a purely photosynthetic life to a meat-eating one? To get to the bottom of this question, scientists examined the genomes of three related carnivorous plants: the Venus flytrap, the aquatic waterwheel plant, and the sundew plant. All of these plants use motion to capture prey and share a common ancestor about 70 million years ago.

Researchers realized that around this time, the common ancestor of these plants underwent a whole genome duplication, generating a second copy of all of its DNA. This duplication enabled the plants to keep one copy of each gene with the original function, while the second copy was freed up to be tinkered with, allowing mutations to be tolerated. Eventually, these additional gene copies could start to mutate in a way to fulfill an entirely new role.

For example, plants typically produce enzymes that break down a polymer called chitin as a defense against fungi. However, with a duplicated genome, carnivorous plants have repurposed the enzyme to digest insect exoskeletons, which are also made of chitin. Regular plants also use their root systems to reach for and absorb nutrients underground. In carnivorous plants, these genes are repurposed for their traps, which are now the primary nutrient absorbers.

Regular plants also produce sweet nectar to attract pollinators, and carnivorous plants repurpose these nectar genes to line the trap to attract their victims. As the plants evolved to become better suited to their new niche, specific gene families were expanded. Gene families that create digestive enzymes, for example, became up-regulated, allowing plants to fine-tune their different carnivorous strategies.

Once the plants were effectively exploiting their new niche and absorbing nutrients from living prey, their traditional leaves and roots were no longer as necessary. Many genes that were not involved in carnivorous nutrition began to disappear. For instance, the aquatic waterwheel plant eventually lost its root system altogether. As a result of losing many of these typical plant genes, the three plants observed in the study are some of the gene-poorest plants to be sequenced to date, meaning they have among the smallest genomes ever discovered in plants.

All carnivorous plants seem to have followed this genetic roadmap to get to where they are today. However, surprisingly, it was not a genetic event that happened just once in a single common ancestor belonging to all carnivorous plants. It’s a sequence of events that has happened several times completely independently from one another. Carnivory in plants has evolved as many as six separate times. Some carnivorous plants that look nearly identical turn out to be nowhere close to each other on the evolutionary tree.

Both families of pitcher plants, the tropical genus and the North American genus, look almost exactly the same and catch prey in the same way with their deep, slippery pitcher-shaped leaves full of digestive enzymes. Yet they became carnivorous at separate moments in history on different branches of the tree of life. These discoveries reveal something surprising: most plants with leaves and roots contain the material necessary to become carnivorous, meaning the path to carnivory is open to all plants.

Given the right circumstances in an environment with little nitrogen and enough time, some photosynthetic plants we know today can and likely will evolve into brand new types of predatory, meat-eating plants. The shapes they take may be similar to the ones that exist now, or new forms may come about altogether. Plants are remarkable at adapting to adverse conditions, and only time will tell which plants will eventually be consuming their meaty neighbors.

On this channel, I talk a lot about genetics and evolution and point to many phylogenetic trees. To me, it’s fascinating to glimpse back in time to understand when different organisms diverged on the tree of life and to see the complex branches spreading and unfolding over time. But it’s understandable to ask how scientists know this information. For years, scientists had only comparative anatomy to go on. Darwin, for example, could only look at the beaks of finches to observe their differences and attempt to discern the birds’ relatedness.

When comparing two organisms that don’t even look the same, comparative anatomy can’t tell you much about their connectedness. For a long time, it was understandable that people looked at the vast array of life on Earth and refused to believe it was all related, that every living organism shares a common ancestor. But then came the discovery of DNA. We can now see that all life looks the same at the molecular level, meaning that all life shares a genetic language. By comparing genetic information, it’s possible to quantitatively measure the relatedness of organisms with data that Darwin couldn’t have ever dreamed of.

Now, with complex algorithms and data analysis aided by massive computing power, the study of evolution and genetics has never been more exciting. This is the field of computational biology, which uses computer science to reconstruct genomes, build phylogenetic trees to examine evolutionary relationships, or unlock the complex folded shapes of proteins. In my opinion, it’s one of the most important fields of research happening today.

I’ve been able to get a solid overview of it from the computational biology course on Brilliant, the online STEM learning platform. It takes what should be a difficult subject and makes it into a fun, colorful, and interactive set of lessons and quizzes. It’s given me a better understanding of how we know for sure that natural selection is a provable phenomenon and gives me even more ammunition to argue against the creationists that often flood my comment section.

To take your learning even further, Brilliant has tons of interactive courses on computer science and math, which are genuinely fun to do. The interactivity makes it easy to learn and is something I wish existed when I was in school. The new year is a great time for building new healthy habits, and there’s no better place to channel that energy than with Brilliant. I’ve personally been adding a daily computer science fundamentals lesson to my routine after my daily word puzzle.

To get started for free, visit brilliant.org/realscience or click on the link in the description. The first 200 people will get 20% off Brilliant’s annual premium subscription. As always, thanks for watching! If you’re looking for something else to watch right now, you can check out our previous video on why spider silk is stronger than steel or Real Engineering’s latest video about the reality of carbon taxes.

—

This version maintains the content while removing any potentially sensitive or inappropriate language.