title: How to catch more prey with less effective traps: explaining the evolution of temporarily inactive traps in carnivorous pitcher plants.
abstract: Carnivorous Nepenthes pitcher plants capture arthropods with specialized slippery surfaces. The key trapping surface, the pitcher rim (peristome), is highly slippery when wetted by rain, nectar or condensation, but not when dry. As natural selection should favour adaptations that maximize prey intake, the evolution of temporarily inactive traps seems paradoxical. Here, we show that intermittent trap deactivation promotes 'batch captures' of ants. Prey surveys revealed that N. rafflesiana pitchers sporadically capture large numbers of ants from the same species. Continuous experimental wetting of the peristome increased the number of non-recruiting prey, but decreased the number of captured ants and shifted their trapping mode from batch to individual capture events. Ant recruitment was also lower to continuously wetted pitchers. Our experimental data fit a simple model that predicts that intermittent, wetness-based trap activation should allow safe access for 'scout' ants under dry conditions, thereby promoting recruitment and ultimately higher prey numbers. The peristome trapping mechanism may therefore represent an adaptation for capturing ants. The relatively rare batch capture events may particularly benefit larger plants with many pitchers. This explains why young plants of many Nepenthes species additionally employ wetness-independent, waxy trapping surfaces.
authors.affiliation: School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK Department of Biology, Universiti Brunei Darussalam, Tungku Link, Gadong 1410, Brunei Darussalam ulrike.bauer@bristol.ac.uk.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Bauer
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
authors.forename: Walter
authors.initials: W
authors.lastname: Federle
authors.affiliation: Department of Animal Ecology and Tropical Biology, University of Würzburg, Am Hubland, Würzburg 97074, Germany.
authors.forename: Hannes
authors.initials: H
authors.lastname: Seidel
authors.affiliation: Department of Biology, Universiti Brunei Darussalam, Tungku Link, Gadong 1410, Brunei Darussalam.
authors.forename: T Ulmar
authors.initials: TU
authors.lastname: Grafe
authors.affiliation: School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Christos C
authors.initials: CC
authors.lastname: Ioannou
mesh_terms: D000818:Animals; D001000:Ants / Q000502:physiology*; D005075:Biological Evolution; D060435:Carnivory; D020387:Food Chain; D019684:Magnoliopsida / Q000502:physiology*
keywords: Nepenthes; carnivorous plants; collective foraging; peristome ‘aquaplaning’; plant–insect interactions; prey capture