Figure 4.

Inversion of trapdoor curvature in U. inflata. (a–c) Buckling of the median door axis, visualized by light sheet fluorescence microscopy. (a) Initially the trapdoor is convex towards the outside of the trap. The force exerted on the door surface owing to water pressure difference Δp between the interior of the trap and the outer medium is balanced by the friction force Π, exerted by the threshold (th) on the trapdoor (do). (b) Following excitation, the trapdoor becomes gradually concave on its outer side, starting at the trigger hair insertion point. The free edge of the trapdoor is pulled away from the threshold contact area by water pressure. (c) Consequently, the door opens wide. (d)–(f) Dynamic simulation of the trapdoor. Parts (d) and (e) correspond to (a) and (b), respectively, while (f) shows the door only half-way from complete inversion. The scale bar is 500 µm.