Patterns of nectar secretion in five Nepenthes species from Brunei Darussalam, Northwest Borneo, and implications for ant-plant relationships.
ABSTRACT The distribution of nectaries and the temporal and spatial pattern of nectar secretion are compared for five Bornean lowland species of Nepenthes (N. a¬lbomarginata, N. b¬icalcarata, N. gracilis, N. mirabilis var. echinostoma, N. rafflesiana) based on results from field studies conducted in Brunei Darussalam, Northwest Borneo. Leaf development together with temporal and spatial pattern of nectar secretion is also given for cultivated Nepenthes bicalcarata, a myrmecophytic species that, in terms of nectar produc¬tion, appears to be exceptional within the genus.
The number of ants trapped in frequently visited pitchers of N. b¬icalcarata and N. mirabilis var. echinostoma was counted over a set period. The percentage of trapped individuals was remarkably small. It ranged from 0.75 to 1.59% of present ants in N. bicalcarata and from 0.34 to 0.42% in N. mirabilis.
The function of extrafloral nectaries in Nepenthes with special reference to N. bicalcarata as well as implications for ant-plant relationships are discussed.
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ABSTRACT: Carnivorous pitcher plants capture prey with modified leaves (pitchers), using diverse mechanisms such as 'insect aquaplaning' on the wet pitcher rim, slippery wax crystals on the inner pitcher wall, and viscoelastic retentive fluids. Here we describe a new trapping mechanism for Nepenthes gracilis which has evolved a unique, semi-slippery wax crystal surface on the underside of the pitcher lid and utilises the impact of rain drops to 'flick' insects into the trap. Depending on the experimental conditions (simulated 'rain', wet after 'rain', or dry), insects were captured mainly by the lid, the peristome, or the inner pitcher wall, respectively. The application of an anti-slip coating to the lower lid surface reduced prey capture in the field. Compared to sympatric N. rafflesiana, N. gracilis pitchers secreted more nectar under the lid and less on the peristome, thereby directing prey mainly towards the lid. The direct contribution to prey capture represents a novel function of the pitcher lid.PLoS ONE 01/2012; 7(6):e38951. · 3.53 Impact Factor
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ABSTRACT: Summary1. Based upon similarity in visual or olfactory appearances, recent studies concluded that mimicry of plants or plant parts occurs in distinct systems, in carnivorous plants that mimic flowers to increase capture success, in thorny plants to defend themselves against predators and in parasitized ants to increase parasite dispersal.2. Taking the example of the carnivorous plant Nepenthes rafflesiana emitting volatiles that insects find attractive, and that also occur in flowers, we argue here that two alternative explanations are more plausible than mimicry: exploitation of perceptual bias and convergence.3. Exploitation of perceptual bias requires only the well-established phenomenon of generalization of rewarding (or unrewarding) experiences; and does not require mimicry’s more specialized conditions of sufficient similarity of the mimic to a specific model, as well as consistency in the overlaps of their phenology and distribution, to cause misidentification by animals.4. Like most flowers, the pitchers of N. rafflesiana offer a nectar reward to visiting insects. Evolution acting on both flowers and pitchers may have converged on the use of similar volatiles entirely independently, simply because these volatiles are effective at attracting nectar-seekers.5. We conclude that not only are there currently no demonstrations of mimicry of a flower’s scent among carnivorous plants, there is also no evidence that mimicry (in any sensory modality) plays any part in carnivory by plants.6. Synthesis. Researchers should guard against prematurely accepting intuitively appealing explanations of mimicry that may hinder the search for the true mechanisms underlying the evolution of some fascinating insect–plant interactions.Journal of Ecology 05/2011; 99(4):899 - 904. · 5.43 Impact Factor
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ABSTRACT: Many plants combat herbivore and pathogen attack indirectly by attracting predators of their herbivores. Here we describe a novel type of insect-plant interaction where a carnivorous plant uses such an indirect defence to prevent nutrient loss to kleptoparasites. The ant Camponotus schmitzi is an obligate inhabitant of the carnivorous pitcher plant Nepenthes bicalcarata in Borneo. It has recently been suggested that this ant-plant interaction is a nutritional mutualism, but the detailed mechanisms and the origin of the ant-derived nutrient supply have remained unexplained. We confirm that N. bicalcarata host plant leaves naturally have an elevated (15)N/(14)N stable isotope abundance ratio (δ(15)N) when colonised by C. schmitzi. This indicates that a higher proportion of the plants' nitrogen is insect-derived when C. schmitzi ants are present (ca. 100%, vs. 77% in uncolonised plants) and that more nitrogen is available to them. We demonstrated direct flux of nutrients from the ants to the host plant in a (15)N pulse-chase experiment. As C. schmitzi ants only feed on nectar and pitcher contents of their host, the elevated foliar δ(15)N cannot be explained by classic ant-feeding (myrmecotrophy) but must originate from a higher efficiency of the pitcher traps. We discovered that C. schmitzi ants not only increase the pitchers' capture efficiency by keeping the pitchers' trapping surfaces clean, but they also reduce nutrient loss from the pitchers by predating dipteran pitcher inhabitants (infauna). Consequently, nutrients the pitchers would have otherwise lost via emerging flies become available as ant colony waste. The plants' prey is therefore conserved by the ants. The interaction between C. schmitzi, N. bicalcarata and dipteran pitcher infauna represents a new type of mutualism where animals mitigate the damage by nutrient thieves to a plant.PLoS ONE 01/2013; 8(5):e63556. · 3.53 Impact Factor