Evidence for alternative trapping strategies in two forms of the pitcher plant, Nepenthes rafflesiana

Abstract

Nepenthes pitchers are specialized leaves that function as insect traps. Several pitcher components may contribute to trapping, including the pitcher fluid, slippery wax crystals and downward-pointing epidermal cells on the inner pitcher wall, and the wetness-dependent pitcher rim (peristome), but the relative importance of these traits is unclear. Mechanisms of prey capture and retention in the field were investigated by quantifying the effect of ‘knock-out’ manipulations of individual pitcher structures, and by testing the ability of pitcher fluids and water to retain insects. Two forms of Nepenthes rafflesiana Jack (‘elongate’ and ‘typical’) with contrasting combinations of pitcher traits were compared. Wax crystals on the inner pitcher wall were found to be the most important trapping structure in the elongate form, whereas the typical form relied primarily on the peristome. The pitcher fluids of both forms, differing markedly in the degree of viscoelasticity, retained significantly more ants than water. The present results show that pitcher plants utilize several mechanisms for prey capture and retention, varying in efficiency and relative importance between forms. It is proposed that these differences represent alternative prey capture strategies that may provide a mechanism to reduce competition and facilitate species co-existence in nutrient-limited habitats.

<I>Nepenthes baramensis</I> (<I>Nepenthaceae</I>) – a new species from north-western Borneo

“…Nepenthes rafflesiana displays considerable morphological variation (Cheek & Jebb 2001, Clarke 2001, Phillipps et al 2008 and in Borneo, a sub-specific taxon that produces, narrow, elongated pitchers has been recorded on a number of occasions (Clarke 1997, Phillipps et al 2008). There are several consistent morphological differences between this elongate taxon and 'typical' N. rafflesiana (Moran 1996, Gaume & Di Giusto 2009, Bauer et al 2011Fig. 1, 2; Table 1, 2), however, their functional significance has not been addressed in recent taxonomic revisions of the genus (Jebb & Cheek 1997, Cheek & Jebb 2001.…”

“…Moran (1996), Gaume & Di Giusto (2009) and Grafe et al (2011) referred to it as N. rafflesiana var. elongata Hort., whereas Bauer et al (2011) used the terms 'elongate form' and 'typical form' to distinguish between them. The name N. rafflesiana var.…”

Mechanism for rapid passive-dynamic prey capture in a pitcher plant

“…The experimental application of an antislip coating to the lower lid surface significantly reduced the prey capture success of N. gracilis pitchers in the field (35). The same treatment applied to the wax crystal-free N. rafflesiana lids had no effect on prey capture (29), suggesting that the wax crystals are crucial for the trap function of the N. gracilis lid.…”

“…It offers safe access to nectar when dry but turns into a deadly slide for insects when wet (26,27). Once trapped, prey is prevented from escaping by the often viscoelastic pitcher fluid (28,29) or by antiadhesive wax crystal surfaces on the inner pitcher wall (30)(31)(32). Fluid viscoelasticity and wax crystal surfaces are only present in a subset of Nepenthes species and are often mutually exclusive (33,34).…”

Reinstatement of Nepenthes hemsleyana (Nepenthaceae), an endemic pitcher plant from Borneo, with a discussion of associated Nepenthes taxa

“…As highlighted by , a number of authors have observed or experimentally demonstrated stable ecological, physiological and morphological differences between two subgroups within the taxon N. rafflesiana sensu Danser, comprising different UV reflectance patterns, scent production and capture rate (Moran 1996), the different ontogeny of pitcher morphology (Gaume & Di Giusto 2009), alternative insect trapping strategies (Bauer et al 2011), and a mutualistic interaction with bats exclusive for one subgroup , Schöner et al 2013. Although the two subgroups were clearly understood by all of the specialists, the nomenclature used has been informal and inconsistent, until Independent from all of the work above, N. rafflesiana var.…”