Slippery surfaces and sticky fluids of carnivorous pitcher plants: biomechanics and ecology
Supervisor: Walter Federle
Insect-plant interactions play an essential role for most ecosystems, but the detailed mechanisms underlying these relationships remain poorly characterized. Carnivorous plants have developed complex structural and functional modifications of plant organs to trap arthropods and extract nutrients, and some insects in turn have developed striking counter-adaptations to overcome the plants’ traps. The aim of this project is to clarify the function and evolutionary development of slippery superhydrophilic capture surfaces and specialized polysaccharide-based trapping fluids in Nepenthes pitcher plants, and to study mechanisms of insect counter-adaptations. The mechanisms evolved in these natural insect-traps may inspire novel synthetic surfaces and materials, as well as new methods for insect pest control.
Nepenthes pitcher plants possess leaves modified into slippery pitfall traps. Insect visitors loose grip on the microstructured, superhydrophilic peristome surface and fall into the pitcher fluid, which can immobilize insects via its polysaccharide-based viscoelastic properties1,2. How do microtopography and wettability of the peristome influence its capture efficiency? How do Nepenthes fluids vary in stickiness and composition, and how does this affect plants and associated arthropods? How do rheological properties vary over time and how can plants cope with fluid dilution by rain? How have trapping mechanisms evolved in the genus Nepenthes? How do specialized arthropods escape the plant’s trapping mechanisms?
Laboratory and field work in SE Asia (mainly Brunei) will be conducted on selected Nepenthes species. The student will 1) characterize the wetting properties of natural Nepenthes surfaces, replicas and synthetic model surfaces 2) quantify insect attachment forces and climbing performance on natural and model substrates under wet and dry conditions, 3) characterize polysaccharide concentration, ion concentration and pH in the field and laboratory, 4) quantify the fluid’s rheology (shear-thinning properties and extensional viscosity) using portable set-ups in the field3, 5) quantify the fluid’s efficiency of capturing insects, 6) study the effects of temperature, humidity and dilution by rain on fluid properties and function, as well as temporal patterns of fluid/polysaccharide secretion, 7) analyze interspecific variation of fluid, peristome and pitcher properties in the context
of available phylogenetic information, and 8) explore adaptations of selected specialist insects to avoid trapping or to move within the plant’s trapping fluids.
The student will be given training in field work and a variety of laboratory techniques including rheometry, high-speed motion analysis on insects, light and electron microscopy as well as phylogenetic methods. Academic training in related physical science topics, including rheology and polymer science, will be provided via existing taught modules.
The project will be supervised by Dr Walter Federle, together with Prof Ian Wilson, Dept of Chemical Engineering, and Dr Ulrike Bauer, University of Bristol. The work will suit a biologist with field work experience and quantitative skills for laboratory work.
Federle, W., Maschwitz, U., Fiala, B., Riederer, M. & Hölldobler, B. 1997. Slippery ant-plants and skilful climbers: Selection and protection of specific ant partners by epicuticular wax blooms in Macaranga (Euphorbiaceae). Oecologia 112, 217-224.
Federle, W. & Rheindt, F. 2005. Macaranga ant-plants hide food from intruders: correlation of food presentation and presence of wax barriers analysed using phylogenetically independent contrasts. Biol. J. Linn. Soc. 84, 177-193.
Feldhaar, H., Fiala, B., Gadau, J., Mohamed, M. & Maschwitz, U. 2003. Molecular phylogeny of Crematogaster subgenus Decacrema ants (Hymenoptera: Formicidae) and the colonization of Macaranga (Euphorbiaceae) trees. Mol. Phyl. Evol. 27, 441-452.