Download A Viscoelastic Deadly Fluid in Carnivorous Pitcher Plants

Background. The carnivorous plants of the genus Nepenthes, widely distributed in the Asian tropics, rely mostly on nutrients
derived from arthropods trapped in their pitcher-shaped leaves and digested by their enzymatic fluid. The genus exhibits
a great diversity of prey and pitcher forms and its mechanism of trapping has long intrigued scientists. The slippery inner
surfaces of the pitchers, which can be waxy or highly wettable, have so far been considered as the key trapping devices.
However, the occurrence of species lacking such epidermal specializations but still effective at trapping insects suggests the
possible implication of other mechanisms. Methodology/Principal Findings. Using a combination of insect bioassays, highspeed
video and rheological measurements, we show that the digestive fluid of Nepenthes rafflesiana is highly viscoelastic and
that this physical property is crucial for the retention of insects in its traps. Trapping efficiency is shown to remain strong even
when the fluid is highly diluted by water, as long as the elastic relaxation time of the fluid is higher than the typical time scale
of insect movements. Conclusions/Significance. This finding challenges the common classification of Nepenthes pitchers as
simple passive traps and is of great adaptive significance for these tropical plants, which are often submitted to high rainfalls
and variations in fluid concentration. The viscoelastic trap constitutes a cryptic but potentially widespread adaptation of
Nepenthes species and could be a homologous trait shared through common ancestry with the sundew (Drosera) flypaper
plants. Such large production of a highly viscoelastic biopolymer fluid in permanent pools is nevertheless unique in the plant
kingdom and suggests novel applications for pest control.