Mechanics reveals the role of peristome geometry in prey capture in carnivorous pitcher plants (Nepenthes)
Carnivorous pitcher plants (Nepenthes) are a striking example of a natural pitfall trap. The traps slippery rim, or peristome, plays a critical role in insect capture via an aquaplaning mechanism that is well documented. Whilst the peristome has received significant research attention, the conspicuous variation in peristome geometry across the genus remains unexplored. We examined the mechanics of prey capture using Nepenthes pitcher plants with divergent peristome geometries. Inspired by living materials, we developed a mathematical model that links the peristomes three-dimensional geometries to the physics of prey capture under the laws of Newtonian mechanics. Linking form and function enables us to test hypotheses related to the function of features such as shape and ornamentation, orientation in a gravitational field, and the presence of teeth, while analysis of the energetic costs and gains of a given geometry provides a means of inferring potential evolutionary pathways. In a separate modeling approach, we show how prey size may correlate with peristome dimensions for optimal capture. Our modeling framework provides a physical platform to understand how divergence in peristome morphology may have evolved in the genus Nepenthes in response to shifts in prey diversity, availability, and size. Significance StatementPitcher plants (Nepenthes) produce an astonishing array of leaf-derived traps into which preys (typically insects) slide from a rim (the peristome). How prey capture varies across this varied genus is a mystery. We hypothesized that insects behave differently depending on peristome size and geometry. We examined the physics of prey capture under the laws of Newtonian mechanics to show that prey size and behavior correlate with peristome shape. We conclude that a diversity of peristomes in Nepenthes evolved in response to variation in prey capture.