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Back Bags Filters. Back Paper Bags Dust Bins. Back Uncategorized Pullman-Holt. Back Attachments. Triggering of sensitive hairs e. Dionaea possesses approximately 20 mm long aerial traps which typically close within — ms [ 3 , 4 ], whereas Aldrovanda develops 2—4 mm long underwater traps which shut within approximately 20— ms [ 5 , 6 ].
It also incorporates the motor zone responsible for turgor change-based motion and numerous trigger hairs. Vegetative morphology of A. Scale bars, a — c 1 cm. Scale bars, e , f 1 mm. Dionaea trap shutting relies on a combination of a turgor change-based slow movement, and a second, fast release of stored elastic energy by a sudden geometric change of its trap lobes snap-buckling. The trap lobes of Aldrovanda, however, do not change curvature during trap closure electronic supplementary material, video S1. Upon triggering, the turgor of inner-lobe epidermal cells located close to the midrib motor zone rapidly decreases due to potassium fluxes [ 7 ].
According to Cameron et al. Although the two species apparently employ different motion principles, hypotheses regarding snap-trap evolution have focused only on the influence of prey size on trap sizes using qualitative models [ 8 , 9 ] but not on other selective factors such as movement mechanics and possible adaptations to the different habitats. There exist no detailed kinematic and functional-morphological analyses of the Aldrovanda trap until now. The kinematic amplification mechanism [ 6 ] is based only on a single trap recording from which also the hypothesis that the midrib might be pretensioned was derived and which also lacks corroborating analyses of the midrib bending and trap closure interrelation, functional—morphological investigations on real traps, as well as a model on potential prestress.
Hence, the actuation principle is unclear because Aldrovanda can be found at the transition between plant movements empowered by elastic instabilities and hydraulics [ 10 ]. We performed detailed biomechanical and functional-morphological analyses in combination with mechanical models and finite-element FE simulations and discuss our findings regarding snap-trap evolution. Plant material of two Aldrovanda vesiculosa ecotypes was provided by L. The cameras were synchronized using the software Motion Studio v.
To trigger the traps electrically, the set-up by Ashida [ 5 ] was adapted. The electrodes were placed into an aquarium volume approx. Dissected, open traps with the midribs facing the cathode, cf. All traps were of the same age mature whorl 7 seen from the plant apex, different individuals cf. Used traps were around 3—4 mm long.
Recording was performed using the aforementioned equipment.
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The high-speed recordings were processed using Fiji v. Durations for each trial were checked for normal distribution with Shapiro—Wilk's test. In order to quantify the midrib deformation from lateral view, from each trial single frames from five randomly chosen high-speed recordings were manually aligned using Photoshop CS5 v. The connection between the basal and apical insertion points of the lobes to the midrib was taken as baseline. The ratios between trap lobe length at the vertex points of Y 1— Y 5 and midrib length were calculated and the resulting ratios taken to normalize the displacement of Y 1— Y 5 for each trap.
By this, the proportion of the Y -displacement in relation to the midrib could be evaluated. The displacement of each of the defined positions relative to the midrib length was measured. Shortening of the midrib in the X -direction during the bending could not be discriminated from the error of measurement and was subsequently excluded from analyses.
Fresh plants were fixed in FAA fixation and entire whorls embedded in Technovit resin. Razorblade cuttings were applied to different regions of closed traps lying in a droplet of water. Hydromechanical effects from the surrounding water were neglected.
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Consequently, in the theoretical limit of a quasi-static actuation, there are no inertia effects or damping in Aldrovanda and were as such neglected in the FE models. A short parameter study regarding the stiffness ratio was conducted for model 3 electronic supplementary material, text S1 and figure S1. For qualitative analysis of deformation behaviour and stress distribution, only the stiffness ratio between the different regions is crucial.
As the material model is simple and the related parameters are not accurately known, it neglects the complexity of the biological tissue. For this reason, no quantitative values for stresses could be evaluated, but the given values allow for a good first-order estimation. For the description of the geometry, different element types were used. Linear components were modelled with shear deformable Timoshenko beam elements, which allow for normal forces as well as bending and shear.
They were discretized by two-node linear elements BEAM Owing to the small thickness of the lobes, shell assumptions apply for two-dimensional regions.
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To first analyse single effects of the trap motion and afterwards a combination of all observed effects, three models with increasing geometrical and mechanical complexity were constructed electronic supplementary material, figure S2. Model 1 served to simulate the basic kinematic behaviour of the trap when the midrib is bent. It is an approximation of the geometry with linear beam elements, where the sum of the cross-sectional areas is equivalent to the actual cross-sectional area of the lobe.
As the focus is on the deformation and bending of the midrib, the displacement constraints are those of a single-span beam. In order to investigate coupling between bending of the midrib and closure of the trap, two different load cases were applied: a distributed vertical load on the midrib 0.
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For a more detailed investigation of the prestress distribution throughout the central region in the closed trap, the real geometry was better approximated by including more elements BEAM The refined geometry is able to represent the lobe curvature more accurately electronic supplementary material, figure S2.
As an experimental investigation of the prestress state in the highly sensitive open trap is not possible, a simulation was performed to deduce this prestress situation from the derived state of the closed trap. More precisely, the open state is deduced via a backward simulation starting from the closed state.
The application of loads compressive stress on midrib caused trap opening. A subsequent unloading would follow the same deformation process backwards for a quasi-static simulation in the given limits of simple elastostatic modelling, as the stable quasi-static process has a convex potential. To avoid rigid body motions, model 2 was constrained like a cantilever beam where all degrees of freedom, three translations and three rotations, were fixed at one side of the midrib, representing the connection to the petiole.
Model 3 was used for i a verification of the prestress effects analysed by model 2, as well as for ii investigation of movement due to turgor change in the motor zone and iii for a combination of the aforementioned two load cases. In order to correctly model the mechanical behaviour of the lobe as a two-dimensional thin-walled structure, shell finite elements were used for the representation of the lobes. The midrib and the lobe margins are modelled by beam elements.
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As in model 2, the displacement constraints represent those of a cantilever beam and the closed state corresponds to the relaxed state. To simulate the effects of turgor decrease in the motor zone, three different load cases were applied. An increase in the temperature represents an increase in turgor, whereas a temperature decrease has the opposite effect.