| Popis: |
Nepenthes pitchers are highly specialised insect traps. Adaptations for trapping include a viscoelastic fluid (uncommon), slippery wax crystals (common) and downward-pointing cells on the inner pitcher wall (ubiquitous), as well as the pitcher rim (peristome, present in almost all species) which is only slippery when wet. ‘Knock-out’ manipulations of individual trap components showed that in the elongate form of N. rafflesiana, the waxy inner pitcher wall was most important whereas the (wax-free) typical form relied mainly on the peristome. Thus they pursued different trapping strategies. In both varieties, the pitcher fluid was highly efficient at retaining prey, regardless of viscoelasticity. The ‘peristome aquaplaning’ mechanism implies that trapping success depends on environmental factors. Combined measurements of capture efficiency, meteorological data and peristome surface wetness showed that capture efficiency varied dramatically and was determined by rain, condensation, and peristome nectary secretion. Prey capture, trapping efficiency, nectar secretion and odour of N. rafflesiana (typical form) also increased significantly over the first two weeks after pitcher opening, while fluid pH and viscoelasticity decreased. The data showed that trapping is a dynamic, age-dependent process and support the importance of ‘peristome aquaplanning’ but not of the fluid’s viscoelasticity for prey capture. Pitcher characteristics vary considerably between Nepenthes species. I recorded morphological parameters from 58 species and mapped them onto published phylogenetic trees. Interspecific variation of trap characteristics indicates the presence of distinct trapping strategies that might have evolved in response to different ecological and environmental factors. |
