Utricularia Trap - Door Opening Mechanism
Door Opening Observations of the trap operation utilizing high-speed videos have provided a new insight into the door opening mechanism. This replaces the long-held notion that the downward push of a trigger lever mechanically pulls the door edge out of the pavement depression, thus creating a small opening for water to enter. This precipitates more water flow, finally forcing the door to flap open completely. To make the idea more plausible, the trigger levers grow on the lower portion of the door just around what appears to be a secondary hinge. This makes it possible to unlatch the tight lock with a minimum of stress, the old theory speculates.
The new idea embraces "buckling" as the key mechanism for door opening. Buckling is a well-studied physical phenomenon and is thoroughly analyzed mathematically. Buckling is characterized by a sudden change of structural states under an increasing load in bladderworts, a flip of the trap door curvature upon triggering, from convex to concave, as seen from the outside of the trap.
When the trap is set, the door is bulging outward. This surface curvature allows the door to withstand a strong outside pressure while a delicate structural equilibrium is maintained. If a trigger lever is touched, the surface area at the base of the lever is disturbed. This slightest perturbation of the door surface under a near-critical pressure causes the door to buckle. The buckling starts where the trigger lever grows and propagates swiftly to a larger area, reversing the curvature of the entire door surface. As the buckling reaches the free edge of the door, the change of the angle of the door edge toward the pavement depression virtually unlocks the door.
Giving in to the
enormous pressure from outside, the door opens in a matter of 1/1000
The sudden inrush of water forces the door to be held in the open
Water continues to flow into the trap, carrying the prey with it.
The elastic energy of the trap walls now released and the trap fully
inflated with no outside pressure,
the door swiftly snaps back to the closed position, unbuckled.
"Carnivorous Plants in the Wilderness")
Calyx lobes : Pinguicula(5)->Genlisea(5)->Polypompholyx(4)->Utricularia(2)
Some speculates that a rolled Pinguicula leaf going down into a moist substrate...
1. Pinguicula -->> rolled leaf growing into moist substrate led to ...
2. Genlisea --- cross section of Genlisea trap is very much reminiscent of Utric trap.... almost identical
3. Primordial trap --- no functional door / maybe mild inward water flow / lobster-pot trap / if door lightly closed, spontaneous triggering captures prey....
4. Polypompholyx trap
5. Terrestrial Utric trap --- generally very small door angle against the threshold.... animal can push itself into the trap --- no trigger lever?
6. Aquatic Utric trap ----- more advanced door triggering mechanism
Evolution: Here are my current thinking and conjecture about Utricularia traps... ---> under construction 2017-April-02
Trigger hairs are not needed for trap triggering.... they are just ornaments, and very important ones at that... /aquatic/terrestrial/U.purpurea (illustr)
Cross section photo by Kiyoshi Shimizu (1966) - Utric winter bud --- primordial trap
Theory of recapitulation ... winter bud shows a very primitive trap -
prototype of terrestrial species of today
Trap is epiascidiate ...like Sarracenia (bladder trap interior = adaxial
- Double-layer .... inevitable consequence since the trap is derived from a leaf (abaxial + adexial epidermis)
- The tip of the trap door corresponds to the leaf tip...
Terrestrial trap - similar to "primitive trap" structure (aquatic traps are more derived)
a) If the door has a small gap ... a mild water flow like Genlisea (less derived than Utricularia). A water animal followed the water flow... or there might not have been any flow at all in a most primordial trap... just a static pouch.
b) If the door is lightly closed --- water animal can push the door and enter (lobster-pot) -OR- spontaneous triggering every so often!!!
- Water is expelled from near the threshold --- into a narrow corridor leading to the door (or along the length of the door). The area serves as a storage for a mouthful of water needed for the next trap firing.... The same water recycled - important consideration for traps not submersed in water... .
Utricularia traps (aquatic) pop when pulled from water......... This is because the air is sucked into the previously set trap. This is a clear proof that the interior of the trap was lower than 1 atm (the atmospheric pressure). In the water, the pressure becomes higher, and at the depth of 10 meter (34 feet) it becomes 2 atm. But bladderworts are floating near the water surface, so it is close to 1 atm (a tiny bit higher than 1 atm, but not lower). So the popping of the trap is not due to higher pressure of the air, but rather due to the disturbance to the trap door when the trap is lifted from the water....
Door Mechanism of Aquatic Trap
Upon triggering, the trap door opens completely in less than one millisecond (1/1000 sec). Probably another millisecond is needed to fully inflate the bladder. And then, with no more external pressure, the door swiftly returns to its closed position in a few milliseconds. So, overall, the entire suction operation of a bladderwort trap takes only 1/100 to 1/200 second to complete.
Buckling at the thinnest area of the door.... the secondary hinge
Illustrations .... simulate the trap door with a sphere .... cut into half .... then half of that.... See from diff angles
The water pumping (out of the trap interior) is continuous. After triggering, it takes only 15-30 minutes to expel the water so that the trap is fully reset and ready again to fire.
After several hours of non-activity (no external stimulation), a trap seems to fire spontaneously, repeating this resetting process.
Copyright (c) 2017 Makoto Honda. All Rights Reserved.