The biomechanics of fast prey capture in aquatic bladderworts

Abstract

Carnivorous plants match their animal prey for speed of movements and hence offer fascinating insights into the evolution of fast movements in plants. Here, we describe the mechanics of prey capture in aquatic bladderworts Utricularia stellaris, which prey on swimming insect larvae or nematodes to supplement their nitrogen intake. The closed Utricularia bladder develops lowerthan-ambient internal pressures by pumping out water from the bladder and thus setting up an elastic instability in bladder walls. When the external sensory trigger hairs on their trapdoor are mechanically stimulated by moving prey, the trapdoor opens within 300 -700 ms, causing strong inward flows that trap their prey. The opening time of the bladder trapdoor is faster than any recorded motion in carnivorous plants. Thus, Utricularia have evolved a unique biomechanical system to gain an advantage over their animal prey.

At the conjunction of biology, chemistry and physics: the fast movements ofDionaea, Aldrovanda, UtriculariaandStylidium

“…The pressure inside the door was decreased slowly with respect to the pressure outside. For a Young's modulus E close to 3 MPa, we observed that the door deforms very little up to a pressure difference of about 16 kPa, in agreement with experimental results (Sydenham and Findlay 1973;Sibaoka 1985a, 1985b), while for larger pressure differences, the panel buckles, slides on the threshold and finally swings wide open Singh et al 2011). Figure 3(g) shows the first indentation that appears in the panel, while Figure 3(h) shows the panel opening wide.…”

“…Highspeed videos show that opening of the door is exceedingly fast. For example, Figures 3(c)-3(e) indicate that it takes less than 1 ms for the panel of an Utricularia australis trap to switch from the closed to the open configuration Vincent et al, 2011) -and yet the traps of U. australis certainly do not belong to the fastest ones of the Utricularia species (see also Singh et al (2011)). Closer examination of Figure 3(d) suggests that the swinging of the panel is preceded by localized curvature inversion and that the door therefore acts as a flexible valve that buckles under the effect of pressure forces rather than as a panel articulated on hinges.…”

Biomechanical analysis of prey capture in the carnivorous Southern bladderwort (Utricularia australis)

“…Future attempts could either try to record the underpressure values inside the bladders simultaneously to the prey capture experiments (cf. refs 5, 6, 12 and 23), or attempt to evaluate suction dynamics by analyzing spontaneous firings, i.e. firings at trap states of critical underpressure without prey touching the trigger hairs.…”

Bacteria can exploit a flagellar buckling instability to change direction

“…At the organismal level, flexibility enhances structural performance, for example by enabling animal bones and plant branches to absorb mechanical energy 10 . Flexibility also underpins a host of dynamic life functions, including locomotion, reproduction and predation, by enabling the storage and swift release of elastic energy, a mechanism used by jumping froghoppers to escape predators 11 , by plants to catapult seeds for dispersal 12 , and by aquatic invertebrates to suck in prey 13 . An extreme consequence of flexibility is the occurrence of mechanical instabilities, such as buckling and fluttering, which in engineered systems are synonymous with failure 14 , but in natural systems can serve functional purpose.…”