The Insane Biology of: The Venus Flytrap

Darwin’s observations began with a peculiar plant in the south of England where he noticed dozens of dead insects or what remained of them adhered to the sticky tentacles of the common sundew plant where Darwin had a hunch that these insect deaths were no accident where he collected specimens and began extensive experimentation to find out if these plants could really be catching these insects on purpose to trap them in order to eat them where he fed his plants salts of ammonia egg white various insects and even small chunks of cheese until soon he was able to scientifically describe their digestive systems and prove unequivocally and for the first time that plants can indeed eat meat demonstrating how systematic experimentation established plant carnivory as a scientific fact.

Today there are over 600 species of carnivorous plants known to science where Darwin’s beloved sundew plant is in the adhesive trap category where prey becomes stuck to extremely sticky droplets where then there are the pitfall traps like pitcher plants where prey falls into the base and is digested where and then there’s the suction traps like the waterwheel plant where aquatic prey animals get sucked into a one-way trap door where but the most iconic of all carnivorous plants are the snap traps like the voracious and enigmatic Venus flytrap demonstrating how carnivorous plants have evolved diverse mechanical strategies for prey capture.

Venus fly traps are naturally found in only one area in the world in the coastal plains of North and South Carolina specifically in one small region 200 kilometers across where they are small plants that live in the open understory of their habitat an understory that remains open due to natural fires that burn away the larger shading plants where and down here amongst the marshy grass is where their killing commences demonstrating how extreme geographic endemism and fire-dependent ecology constrain Venus flytrap distribution to a single narrow biogeographic zone.

The trap of the Venus flytrap is a leaf with two lobes connected at a hinge on its stalk where the lobes sit waiting curved in the open position luring prey insects with sweet smelling nectar where if something like a fly spider or beetle lands on or crawls across the gaping jaws it risks touching any of the fly trap’s six sensory hairs the hairs that give the plant the signal to snap shut demonstrating how modified leaf architecture integrates chemical lures with mechanosensory trigger systems.

If it touches a single hair the plant won’t budge and the insect is safe for now but a deadly timer has begun within the plant a crucial 30 seconds that will determine if the insect lives or dies where if the insect touches another sensory hair within the 30-second window the insect is doomed where upon the second touch the lobes snap shut faster than the blink of an eye where the reason it needs two triggers within a 30 second window is to prevent the plant from closing erroneously and wasting energy for something like a raindrop or a twig demonstrating how temporal integration prevents false-positive triggering while conserving metabolic resources.

The plant’s movement is controlled by an electrical signal created by the hairs where when a hair is bent by touch it acts as a lever that stretches the envelopes of cell membranes at its base where the stretching causes ion channels to burst open where positively charged calcium ions flood out creating an action potential aka an electrical signal that spreads from the hair over the entire flap trap where after two action potentials the trap snaps shut demonstrating how mechanotransduction converts mechanical stimuli into propagating electrical signals analogous to animal nerve impulses.

The initially concave trap lobes move towards each other and eventually change to a convex state where the movement is faster than the blink of an eye representing one of the fastest movements in the plant kingdom where the transition from concave to convex is driven by changes in turgor pressure in the cell walls demonstrating how bistable elastic structures enable explosive shape transitions through hydraulic pressure redistribution.

Researchers had a hunch that it had to do with the changes in calcium concentrations inside the leaves where to test this they genetically modified Venus fly traps to emit green fluorescence when calcium ions were present in the leaf cells where when the first hair is touched a flood of green overtakes the leaf showing a big presence of calcium ions but as the seconds pass the concentration slowly starts to drop where but if a second hair is touched the calcium concentration again increases flooding the leaf with even more green where it’s only when a certain threshold is reached in the calcium concentration that the trap snaps shut where this threshold can only be reached if the two stimuli occur within 30 seconds demonstrating how calcium concentration functions as a temporal integrator converting stimulus frequency into threshold-based binary decisions.

The plant requires sustained wiggling within its jaws to fully seal and begin the deadly digesting process where this ensures it’s using its digestive resources only on hearty insect meals where but once a wriggling bug does cause the trap to fully seal it’s no longer a mouth but a stomach where you could indeed get the fly trap to close on the cheese initially but after a few hours it will reopen rejecting your generous gift demonstrating how sustained mechanical stimulation functions as a prey quality assessment preventing digestive investment in non-nutritive substrates.

Digestive juices flood into the closed trap where the pH drops dramatically and meat digesting enzymes similar to ones in our stomachs start to break down the trapped creature where the more the prey fights and wriggles the more digestive enzymes are released where if you’re a bug the more you struggle the faster you die where slowly over the course of a week or so the insect’s body is liquefied and the lining of the trap absorbs the nutrients demonstrating how struggle-responsive enzyme secretion optimizes digestion kinetics through positive feedback between prey movement and proteolytic output.

While the Venus fly trap does extract some energy from its food like we do what it’s really after when it kills prey is not the insect’s calorie content but rather it’s nitrogen where plants need nitrogen in order to successfully carry out photosynthesis as it’s a major component of chlorophyll where it’s also a major component of amino acids the building block of proteins and is needed for general growth and regeneration in the plant without nitrogen a plant will wither and die where the Venus fly trap gets between 50 and 75% of its nitrogen from chowing down on insects demonstrating how carnivory functions primarily as nitrogen supplementation rather than energy acquisition in nutrient-deficient habitats.

That 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 fly trap where a similar story is true for the other carnivorous plants where pitcher plants for example grow in marshy nutrient poor soil as does the sundew where it seems pretty clear then that carnivory evolved in plants to cope with nutrient scarce soils demonstrating how extreme edaphic stress selects for heterotrophic nitrogen acquisition as adaptive compensation for soil nutrient limitation.

Scientists examined the genomes of three related carnivorous plants the Venus fly trap the aquatic waterwheel plant and the sundew plant where all of these plants use motion to capture prey and shared a common ancestor about 70 million years ago where researchers realized that around this time 70 million years ago these plants’ common ancestor underwent a whole genome duplication generating a second copy of all of its DNA where this duplication enabled the plants to keep one copy of each gene with the original function where the second copy was thus freed up to be tinkered with where mutations could be tolerated demonstrating how whole genome duplication provides genetic raw material for evolutionary innovation through relaxed selection on redundant gene copies.

Plants typically produce enzymes that break down a polymer called chitin as a defense against fungi but with a duplicated genome carnivorous plants have repurposed the enzyme to digest insect exoskeletons which are also made of chitin where typical plants also use their root system to reach for and absorb nutrients underground where in carnivorous plants these genes are repurposed for their traps which are now the primary nutrient absorber where regular plants also produce sweet nectar to attract pollinators and now carnivorous plants repurpose these nectar genes to line the trap to attract their victims demonstrating how gene duplication enables functional cooption where ancestral defensive and reproductive genes acquire novel predatory roles.

Then as the plants evolved to become even better suited to their new niche specific gene families were expanded where gene families that create digestive enzymes for example became up-regulated where this allowed plants to fine-tune their different carnivorous strategies where then 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 where many genes that were not involved in carnivorous nutrition began to disappear demonstrating how adaptive evolution involves both gene family amplification for novel functions and reductive evolution through loss of ancestral traits.

For instance aquatic water wheel plants eventually lost their root system altogether where 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 where all carnivorous plants seem to have followed this genetic road map to get to where they are today demonstrating how specialization on carnivory enables genome reduction through loss of genes associated with ancestral nutrient acquisition strategies.

However surprisingly it was not a genetic event that happened just once in a single common ancestor belonging to all carnivorous plants where it’s a sequence of events that has happened several times completely independently from one another where carnivory in plants has evolved as many as six separate times where some carnivorous plants that even look nearly identical turn out to be nowhere close to each other on the evolutionary tree demonstrating how convergent evolution repeatedly produces similar solutions to nutrient limitation across distantly related plant lineages.

Both families of pitcher plants the tropical genus and the North American genus look almost exactly the same and catch prey in the same exact 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 demonstrating how similar selective pressures drive convergent evolution of functionally identical trap morphologies in phylogenetically distant lineages.

Most plants with leaves and roots contain the material necessary to become carnivorous meaning the path to carnivory is open to all plants where given the right circumstances in an environment with little nitrogen and with enough time some photosynthetic plants we know today can and likely will evolve into brand new types of predatory meat-eating plants where the shapes they take may be similar to the ones that exist now or new forms may come about altogether demonstrating how genetic preadaptation in all plants creates evolutionary potential for future carnivory given appropriate selective pressures.