Journal Article

Adaptive significance and ontogenetic variability of the waxy zone in <i>Nepenthes rafflesiana</i>

Laurence Gaume and Bruno Di Giusto

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 104, issue 7, pages 1281-1291
Published in print December 2009 | ISSN: 0305-7364
Published online October 2009 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcp238
Adaptive significance and ontogenetic variability of the waxy zone in Nepenthes rafflesiana

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims

The slippery waxy zone in the upper part of pitchers has long been considered the key trapping structure of the Nepenthes carnivorous plants; however, the presence of wax is reported to be variable within and between species of this species-rich genus. This study raises the question of the adaptive significance of the waxy zone and investigates the basis for an ontogenetic cause of its variability and correlation with pitcher shape.

Methods

In Brunei (Borneo) the expression of the waxy zone throughout plant ontogeny was studied in two taxa of the Nepenthes rafflesiana complex, typica and elongata, which differ in pitcher shape and size. We also tested the adaptive significance of this zone by comparing the trapping efficiency and the number of prey captured of wax-bearing and wax-lacking plants.

Key Results

In elongata, the waxy zone is always well expanded and the elongated pitchers change little in form during plant development. Wax efficiently traps experimental ants but the number of captured prey in pitchers is low. In contrast, in typica, the waxy zone is reduced in successively produced pitchers until it is lost at the end of the plant's juvenile stage. The form of pitchers thus changes continuously throughout plant ontogeny, from elongated to ovoid. In typica, the number of captured prey is greater, but the role of wax in trapping is minor compared with that of the digestive liquid, and waxy plants do not show a higher insect retention and prey abundance as compared with non-waxy plants.

Conclusions

The waxy zone is not always a key trapping structure in Nepenthes and can be lost when supplanted by more efficient features. This study points out how pitcher structure is submitted to selection, and that evolutionary changes in developmental mechanisms could play a role in the morphological diversity of Nepenthes.

Keywords: Carnivorous plant; developmental evolution; digestive liquid; epicuticular wax; insect trapping; heteroblasty; heterochrony; leaf form; morphological diversity; Nepenthes rafflesiana; ontogenetic change; pitcher plant

Journal Article.  7901 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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