Smooth or with a Snap! Biomechanics of Trap Reopening in the Venus Flytrap (Dionaea muscipula)

Abstract

Fast snapping in the carnivorous Venus flytrap ( Dionaea muscipula ) involves trap lobe bending and abrupt curvature inversion (snap‐buckling), but how do these traps reopen? Here, the trap reopening mechanics in two different D. muscipula clones, producing normal‐sized (N traps, max. ≈3 cm in length) and large traps (L traps, max. ≈4.5 cm in length) are investigated. Time‐lapse experiments reveal that both N and L traps can reopen by smooth and continuous outward lobe bending, but only L traps can undergo smooth bending followed by a much faster snap‐through of the lobes. Additionally, L traps can reopen asynchronously, with one of the lobes moving before the other. This study challenges the current consensus on trap reopening, which describes it as a slow, smooth process driven by hydraulics and cell growth and/or expansion. Based on the results gained via three‐dimensional digital image correlation (3D‐DIC), morphological and mechanical investigations, the differences in trap reopening are proposed to stem from a combination of size and slenderness of individual traps. This study elucidates trap reopening processes in the (in)famous Dionaea snap traps – unique shape‐shifting structures of great interest for plant biomechanics, functional morphology, and applications in biomimetics, i.e., soft robotics.

Shapeshifting in the Venus flytrap (Dionaea muscipula): Morphological and biomechanical adaptations and the potential costs of a failed hunting cycle

“…Trap reopening after fast snap-closure without prey capture is the final stage of the short hunting cycle (Figure 1C). Traps usually reopen within 16-44 h, with smaller morphotypes reported to have shorter median reopening times than the larger ones (Volkov et al, 2011;Poppinga et al, 2016;Durak et al, 2022). Each trap can only reopen a finite amount of times (usually 3-12), before losing functionality (Bailey and McPherson, 2012).…”

“…However, previous attempts to assess changes in cell length during trap reopening cycle yielded inconclusive results (Fagerberg and Howe, 1996). Trap reopening can follow several scenarios, with both trap lobes bending outwards homogenously (Volkov et al, 2011;Poppinga et al, 2016) or asynchronously, with one lobe opening before the other, or with a distinct "rim-pop" at the beginning of the reopening sequence (Durak et al, 2022). The "rim-pop" was reported to occur right at the edge of both normal-sized and large traps alike during the initial reopening stage, and is most likely caused by the sticky nectar deposited around the rim of the trap (Mozingo et al, 1970;Juniper et al, 1989), or can result from the resistance arising from the marginal cilia ("teeth") sliding apart.…”

“…The "rim-pop" was reported to occur right at the edge of both normal-sized and large traps alike during the initial reopening stage, and is most likely caused by the sticky nectar deposited around the rim of the trap (Mozingo et al, 1970;Juniper et al, 1989), or can result from the resistance arising from the marginal cilia ("teeth") sliding apart. Whether the lobes open synchronously or not, the reopening process on the global scale can either commence in a smooth, homogenous fashion or with a snap-buckling step towards the end of the reopening sequence (Durak et al, 2022). Upon closer investigation of the reopening scenarios, Durak et al (2022) concluded that the observed behavior is highly dependent on the trap size and slenderness.…”

“…Whether the lobes open synchronously or not, the reopening process on the global scale can either commence in a smooth, homogenous fashion or with a snap-buckling step towards the end of the reopening sequence (Durak et al, 2022). Upon closer investigation of the reopening scenarios, Durak et al (2022) concluded that the observed behavior is highly dependent on the trap size and slenderness. In their study, they show that traps below 3 cm in length [normal-sized (N) traps] open exclusively via a smooth, homogenous reopening sequence in a synchronous outwards lobe bending motion.…”

“…In contrast, traps ≈ 3-4.3 cm [large (L) traps] can reopen not only in a synchronous or asynchronous manner, but 3.85% of the L traps were additionally able to incorporate a reverse snap-through step into the reopening sequence. Since the snap-through process was previously considered energetically costly and even impossible to perform due to the mechanics involved (Fagerberg and Howe, 1996;Poppinga et al, 2016), Durak et al (2022) set out to investigate the potential of the trap morphometrics playing a role in determining whether a trap is capable of going through the snap-through during reopening or not. As comparison of the distribution of the evolving strain patterns between N and L traps did not yield any significant differences, Durak et al (2022) looked into the overall slenderness of the traps within these two morphotype categories.…”