Catapulting tentacles in a sticky carnivorous plant

Abstract

Among trapping mechanisms in carnivorous plants, those termed 'active' have especially fascinated scientists since Charles Darwin's early works because trap movements are involved. Fast snap-trapping and suction of prey are two of the most spectacular examples for how these plants actively catch animals, mainly arthropods, for a substantial nutrient supply. We show that Drosera glanduligera, a sundew from southern Australia, features a sophisticated catapult mechanism: Prey animals walking near the edge of the sundew trigger a touch-sensitive snap-tentacle, which swiftly catapults them onto adjacent sticky glue-tentacles; the insects are then slowly drawn within the concave trap leaf by sticky tentacles. This is the first detailed documentation and analysis of such catapult-flypaper traps in action and highlights a unique and surprisingly complex mechanical adaptation to carnivory.

Figure 1. Trap leaves of Drosera glanduligera.

(A) A naturally growing plant; note the peripheral, non-sticky snap-tentacles and the deeply concave trap leaves covered with glue-tentacles. (B) A cultivated plant; the snap-tentacles extend from the lamina margin. (C) A caught fruit fly; the prey is deeply drawn within the concave leaf blade.

Figure 2. Snap-tentacle morphology and anatomy.

(A) SEM micrographs of excised snap-tentacles. Left image: The bilateral symmetric tentacle is characterized by a gland raised above the terminal disc on the tentacle head. The gland does not produce mucilage. The hinge-zone is clearly visible. Right image: Fracture of adaxial epidermal cells in the hinge-zone (arrows) that presumably is due to local cell buckling caused by the compressive stresses acting on the adaxial side during the fast tentacle bending motion. (B) Transverse section of the hinge-zone, stained with toluidine. The abaxial epidermal cells are smaller than the adaxial epidermal cells. Both epidermis and parenchyma do not feature pronounced wall thickenings.

Figure 3. Snap-tentacle kinematics.

(A) Each step between 1 and 10 depicts a 5 ms time interval. (B) Speed (blue) and acceleration (red) of the tentacle head during the bending motion (for a higher resolved curve see Fig. S1); the numbers correspond to the numbers depicted in (A).