With a Flick of the Lid: A Novel Trapping Mechanism in <em>Nepenthes gracilis</em> Pitcher Plants

Carnivorous pitcher plants capture prey with modified leaves (pitchers), using diverse mechanisms such as ‘insect aquaplaning’ on the wet pitcher rim, slippery wax crystals on the inner pitcher wall, and viscoelastic retentive fluids. Here we describe a new trapping mechanism for Nepenthes gracilis which has evolved a unique, semi-slippery wax crystal surface on the underside of the pitcher lid and utilises the impact of rain drops to ‘flick’ insects into the trap. Depending on the experimental conditions (simulated ‘rain’, wet after ‘rain’, or dry), insects were captured mainly by the lid, the peristome, or the inner pitcher wall, respectively. The application of an anti-slip coating to the lower lid surface reduced prey capture in the field. Compared to sympatric N. rafflesiana, N. gracilis pitchers secreted more nectar under the lid and less on the peristome, thereby directing prey mainly towards the lid. The direct contribution to prey capture represents a novel function of the pitcher lid.食虫猪笼草（Carnivorous pitcher plant）通过特化叶片形成的捕虫笼（pitcher）捕获猎物，其具备多种捕虫机制，例如湿润笼口上的"昆虫滑水（insect aquaplaning）"效应、笼内壁的光滑蜡质晶体，以及具有黏弹性的滞留性体液。本文报道了细猪笼草（Nepenthes gracilis）的一种全新捕虫机制：该物种在捕虫笼笼盖的下表面演化出了独特的半光滑蜡质晶体表面，并借助雨滴的冲击力将昆虫"弹入"陷阱。根据实验设置的不同条件（模拟降雨、降雨后湿润状态或干燥状态），昆虫分别主要被笼盖、笼口周缘（peristome）以及笼内壁捕获。在野外实验中，向笼盖下表面涂抹防滑涂层后，猎物捕获量显著下降。与同域分布的莱佛士猪笼草（N. rafflesiana）相比，细猪笼草的捕虫笼在笼盖下分泌的蜜汁更多，而在笼口周缘的蜜汁分泌量更少，借此将猎物主要引导至笼盖区域。这一直接参与猎物捕获的功能，代表了捕虫笼笼盖的全新生理功能。