Papers by Bruno Di Giusto
Plants with simple architecture and strong constraints on their growth may offer critical insight... more Plants with simple architecture and strong constraints on their growth may offer critical insights into how growth strategies affect the tolerance of plants to herbivory. Although Dioscorea praehensilis, a wild yam of African forests, is perennial, both aerial apparatus and tuber are annually renewed. Each year, the tuber produces a single stem that climbs from the ground to the forest canopy. This stem bears no leaves and no branches until it reaches optimal light conditions. Once in the canopy, the plant's production fuels the filling of a new tuber before the plant dies back to the ground. We hypothesized that if deprived of ant defense, the leafless growth phase is a vulnerable part of the cycle, during which a small amount of herbivory entails a high cost in terms of loss of opportunity. We compared the growth of stems bearing ants or not as well as of intact stems and stems subjected to simulated or natural herbivory. Ants reduce herbivory; herbivory delays arrival to the canopy and shortens the season of production. Artificially prolonging the stem growth to the canopy increased plant mortality in the following year and, in surviving plants, reduced the stem diameter and likely the underground reserves produced. Tuber size is a key variable in plant performance as it affects both the size of the aerial apparatus and the duration of its single season of production. Aerial apparatus and tuber are thus locked into a cycle of reciprocal annual renewal. Costs due to loss of opportunity may play a major role in plant tolerance to herbivory, especially when architectural constraints interact with ecological conditions to shape the plant's growth strategy.
Sexual specialization in phenology in dioecious Ficus benguetensis and its consequences for the mutualism
Botanical Studies, 2015
ABSTRACT
Functional Surfaces in Biology, 2009
Annals of Botany, 2007
Aims Species of the Nepenthaceae family are under-represented in studies of leaf traits and the c... more Aims Species of the Nepenthaceae family are under-represented in studies of leaf traits and the consequent view of mineral nutrition and limitation in carnivorous plants. This study is aimed to complement existing data on leaf traits of carnivorous plants. † Methods Physico-chemical properties, including construction costs (CC), of the assimilatory organs (leaf and pitcher) of a guild of lowland Nepenthes species inhabiting heath and/or peat swamp forests of Brunei, Northern Borneo were determined. † Key Results Stoichiometry analyses indicate that Nepenthes species are nitrogen limited. Most traits vary appreciably across species, but greater variations exist between the assimilatory organs. Organ mass per unit area, dry matter tissue concentration (density), nitrogen (N), phosphorus (P), carbon, heat of combustion (H c ) and CC values were higher in the leaf relative to the pitcher, while organ thickness, potassium (K) and ash showed the opposite trend. Cross-species correlations indicate that joint rather than individual consideration of the leaf and the pitcher give better predictive relationships between variables, signalling tight coupling and functional interdependence of the two assimilatory organs. Across species, mass-based CC did not vary with N or P, but increases significantly with tissue density, carbon and H c , and decreases with K and ash contents. Area-based CC gave the same trends (though weaker in strength) in addition to a significant positive correlation with tissue mass per unit area. † Conclusions The lower CC value for the pitcher is in agreement with the concept of low marginal cost for carnivory relative to conventional autotrophy. The poor explanatory power of N, P or N : P ratio with CC suggests that factors other than production of expensive photosynthetic machinery (which calls for a high N input), including concentrations of lignin, wax/lipids or osmoregulatory ions like K þ , may give a better explanation of the CC variation across Nepenthes species.
Carnivorous pitcher plants capture prey with modified leaves (pitchers), using diverse mechanisms... more 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.
Relations interspécifiques igname-fourmis-chrysomèle
L'igname et les fourmis: effets de la défense biotique et de l'herbivorie sur la croissance d'une liane tropicale à tubercule souterrain
Journal of …, Jan 1, 2010
1. Nepenthes rafflesiana is a carnivorous vine from Borneo characterized by an ontogenetic pitche... more 1. Nepenthes rafflesiana is a carnivorous vine from Borneo characterized by an ontogenetic pitcher dimorphism with aerial (upper) and ground (lower) pitchers of different morphologies. Previous studies have shown that fragrant upper pitchers of climbing parts of the plant are more effective in trapping flying insects than non-fragrant lower pitchers, which are essentially restricted to an ant diet. We tested the hypotheses that odours are effective cues for prey attraction in this carnivorous plant and that upper pitchers biochemically mimic flowers in their olfactory cues. 2. The visitor diversity and the scent composition of each pitcher type were determined for different sites and periods during field studies in Borneo. Olfactometer bioassays were conducted using fruit flies and ants as models for flying flower-visitors and non-flying visitors, respectively. 3. Fifty-four volatile compounds were identified and the analysis of their relative quantities in the blends showed significant differences between pitcher types. The blends of lower pitchers contained some aliphatics and terpenoids but were poor in benzenoids. Upper pitchers differed from lower ones in that they attracted a greater quantity and diversity of insects, including a guild of flower-visitors absent from the visitor spectrum of lower pitchers. Upper pitchers also emitted a greater quantity of odours and a larger spectrum of volatiles, including some terpenoids and benzenoids that often characterize the sweet scents classically found in flower blends. Choice bioassays showed that, in absence of any visual cue, the scents of the nectariferous pitcher rim (peristome) were particularly attractive to ants and flies, and those of upper pitchers were more attractive to flies than those of lower pitchers. 4. Synthesis. This study demonstrates the use of scent by Nepenthes carnivorous plants to mediate prey attraction. The climbing part of the plant produces pitcher-modified leaves that mimic flower olfactory cues and suggest an evolutionary convergent strategy with that of generalist pollination systems.
The trophic structure of tropical ant-plant-herbivore interactions: community consequences and coevolutionary dynamics
Biotic interactions in …, Jan 1, 2005
... nities. This part draws heavily from important recent work by Davidson and colleagues (Davids... more ... nities. This part draws heavily from important recent work by Davidson and colleagues (Davidson 1997; Davidson et al. ... Page 411. TROPHIC STRUCTURE OF ANT-PLANT-HERBIVORE INTERACTIONS 391 2001; Davidson et al. 2003 ...
Journal of Ecology, Jan 1, 2010
1. Nepenthes rafflesiana is a carnivorous vine from Borneo characterized by an ontogenetic pitche... more 1. Nepenthes rafflesiana is a carnivorous vine from Borneo characterized by an ontogenetic pitcher dimorphism with aerial (upper) and ground (lower) pitchers of different morphologies. Previous studies have shown that fragrant upper pitchers of climbing parts of the plant are more effective in trapping flying insects than non-fragrant lower pitchers, which are essentially restricted to an ant diet. We tested the hypotheses that odours are effective cues for prey attraction in this carnivorous plant and that upper pitchers biochemically mimic flowers in their olfactory cues.2. The visitor diversity and the scent composition of each pitcher type were determined for different sites and periods during field studies in Borneo. Olfactometer bioassays were conducted using fruit flies and ants as models for flying flower-visitors and non-flying visitors, respectively.3. Fifty-four volatile compounds were identified and the analysis of their relative quantities in the blends showed significant differences between pitcher types. The blends of lower pitchers contained some aliphatics and terpenoids but were poor in benzenoids. Upper pitchers differed from lower ones in that they attracted a greater quantity and diversity of insects, including a guild of flower-visitors absent from the visitor spectrum of lower pitchers. Upper pitchers also emitted a greater quantity of odours and a larger spectrum of volatiles, including some terpenoids and benzenoids that often characterize the sweet scents classically found in flower blends. Choice bioassays showed that, in absence of any visual cue, the scents of the nectariferous pitcher rim (peristome) were particularly attractive to ants and flies, and those of upper pitchers were more attractive to flies than those of lower pitchers.4. Synthesis. This study demonstrates the use of scent by Nepenthes carnivorous plants to mediate prey attraction. The climbing part of the plant produces pitcher-modified leaves that mimic flower olfactory cues and suggest an evolutionary convergent strategy with that of generalist pollination systems.
Annals of Botany, Jan 1, 2009
Aims The slippery waxy zone in the upper part of pitchers has long been considered the key trappi... more 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.
Annals of Botany, Jan 1, 2007
Aims Species of the Nepenthaceae family are under-represented in studies of leaf traits and the c... more Aims Species of the Nepenthaceae family are under-represented in studies of leaf traits and the consequent view of mineral nutrition and limitation in carnivorous plants. This study is aimed to complement existing data on leaf traits of carnivorous plants. † Methods Physico-chemical properties, including construction costs (CC), of the assimilatory organs (leaf and pitcher) of a guild of lowland Nepenthes species inhabiting heath and/or peat swamp forests of Brunei, Northern Borneo were determined. † Key Results Stoichiometry analyses indicate that Nepenthes species are nitrogen limited. Most traits vary appreciably across species, but greater variations exist between the assimilatory organs. Organ mass per unit area, dry matter tissue concentration (density), nitrogen (N), phosphorus (P), carbon, heat of combustion (H c ) and CC values were higher in the leaf relative to the pitcher, while organ thickness, potassium (K) and ash showed the opposite trend. Cross-species correlations indicate that joint rather than individual consideration of the leaf and the pitcher give better predictive relationships between variables, signalling tight coupling and functional interdependence of the two assimilatory organs. Across species, mass-based CC did not vary with N or P, but increases significantly with tissue density, carbon and H c , and decreases with K and ash contents. Area-based CC gave the same trends (though weaker in strength) in addition to a significant positive correlation with tissue mass per unit area. † Conclusions The lower CC value for the pitcher is in agreement with the concept of low marginal cost for carnivory relative to conventional autotrophy. The poor explanatory power of N, P or N : P ratio with CC suggests that factors other than production of expensive photosynthetic machinery (which calls for a high N input), including concentrations of lignin, wax/lipids or osmoregulatory ions like K þ , may give a better explanation of the CC variation across Nepenthes species.
Journal of Biosciences, Jan 1, 2008
Mechanisms that improve prey richness in carnivorous plants may involve three crucial phases of t... more Mechanisms that improve prey richness in carnivorous plants may involve three crucial phases of trapping: attraction, capture and retention. Nepenthes rafflesiana var. typica is an insectivorous pitcher plant that is widespread in northern Borneo. It exhibits ontogenetic pitcher dimorphism with the upper pitchers trapping more flying prey than the lower pitchers. While this difference in prey composition has been ascribed to differences in attraction, the contribution of capture and retention has been overlooked. This study focused on distinguishing between the prey trapping mechanisms, and assessing their relative contribution to prey diversity. Arthropod richness and diversity of both visitors and prey in the two types of pitchers were analysed to quantify the relative contribution of attraction to prey trapping. Rate of insect visits to the different pitcher parts and the presence or absence of a sweet fragrance was recorded to clarify the origin and mechanism of attraction. The mechanism of retention was studied by insect bioassays and measurements of fluid viscosity. Nepenthes rafflesiana was found to trap a broader prey spectrum than that previously described for any Nepenthes species, with the upper pitchers attracting and trapping a greater quantity and diversity of prey items than the lower pitchers. Capture efficiency was low compared with attraction or retention efficiency. Fragrance of the peristome, or nectar rim, accounted mainly for the observed non-specific, better prey attraction by the upper pitchers, while the retentive properties of the viscous fluid in these upper pitchers arguably explains the species richness of their flying prey. The pitchers of N. rafflesiana are therefore more than simple pitfall traps and the digestive fluid plays an important yet unsuspected role in the ecological success of the species.
Benefits to plants in facultative ant protection mutualisms are highly variable. This allows exam... more Benefits to plants in facultative ant protection mutualisms are highly variable. This allows examination of the sources of this variation and the mechanisms by which ants protect plants. We studied opportunistic interactions between ants and an extrafloral nectary-bearing vine, Dioscorea praehensilis, during 3 different years. Variation in plant protection among years was striking. Several factors affected the effectiveness of the biotic defence. Stems recently emerged from the underground tuber were self-supporting, contacting no other plants and encountering few
foraging ants. Stems then became lianescent, and contact with supporting plants greatly increased ant recruitment.
Both species and number of ant workers influenced the effect of ants on the major herbivore, the chrysomelid beetle Lilioceris latipennis. Protective actions included limitation of oviposition (reduction in the number of eggs laid on the plant) and predation, leading to increased larval mortality.
The probability of successful predation was strongly dependent on larval size. If temporarily low ant-patrolling activity allows larvae to grow beyond a critical size, their mechanical (thick integument) or chemical (plant-derived compounds in a fecal shield) defences become more effective against ants. Secondary metabolites derived from the host plant thus appear to be important for the anti-predator mechanisms of this beetle, being necessary for its survival and reproduction on a host plant that actively recruits ants as a biotic defence against herbivores.
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Papers by Bruno Di Giusto
foraging ants. Stems then became lianescent, and contact with supporting plants greatly increased ant recruitment.
Both species and number of ant workers influenced the effect of ants on the major herbivore, the chrysomelid beetle Lilioceris latipennis. Protective actions included limitation of oviposition (reduction in the number of eggs laid on the plant) and predation, leading to increased larval mortality.
The probability of successful predation was strongly dependent on larval size. If temporarily low ant-patrolling activity allows larvae to grow beyond a critical size, their mechanical (thick integument) or chemical (plant-derived compounds in a fecal shield) defences become more effective against ants. Secondary metabolites derived from the host plant thus appear to be important for the anti-predator mechanisms of this beetle, being necessary for its survival and reproduction on a host plant that actively recruits ants as a biotic defence against herbivores.