Feeding on prey increases photosynthetic efficiency in the carnivorous sundew Drosera capensis

Backround and Aims

It has been suggested that the rate of net photosynthesis (A_N) of carnivorous plants increases in response to prey capture and nutrient uptake; however, data confirming the benefit from carnivory in terms of increased A_N are scarce and unclear. The principal aim of our study was to investigate the photosynthetic benefit from prey capture in the carnivorous sundew Drosera capensis.

Methods

Prey attraction experiments were performed, with measurements and visualization of enzyme activities, elemental analysis and pigment quantification together with simultaneous measurements of gas exchange and chlorophyll a fluorescence in D. capensis in response to feeding with fruit flies (Drosophila melanogaster).

Key Results

Red coloration of tentacles did not act as a signal to attract fruit flies onto the traps. Phosphatase, phophodiesterase and protease activities were induced 24 h after prey capture. These activities are consistent with the depletion of phosphorus and nitrogen from digested prey and a significant increase in their content in leaf tissue after 10 weeks. Mechanical stimulation of tentacle glands alone was not sufficient to induce proteolytic activity. Activities of β-D-glucosidases and N-acetyl-β-D-glucosaminidases in the tentacle mucilage were not detected. The uptake of phosphorus from prey was more efficient than that of nitrogen and caused the foliar N:P ratio to decrease; the contents of other elements (K, Ca, Mg) decreased slightly in fed plants. Increased foliar N and P contents resulted in a significant increase in the aboveground plant biomass, the number of leaves and chlorophyll content as well as A_N, maximum quantum yield (F_v/F_m) and effective photochemical quantum yield of photosystem II (Φ_PSII).

Conclusions

According to the stoichiometric relationships among different nutrients, the growth of unfed D. capensis plants was P-limited. This P-limitation was markedly alleviated by feeding on fruit flies and resulted in improved plant nutrient status and photosynthetic performance. This study supports the original cost/benefit model proposed by T. Givnish almost 30 years ago and underlines the importance of plant carnivory for increasing phosphorus, and thereby photosynthesis.     

Plant pressure sensitive adhesives: similar chemical properties in distantly related plant lineages

Main conclusion

A mixture of resins based on aliphatic esters and carboxylic acids occurs in distantly related genera Peperomia and Roridula , serving different functions as adhesion in seed dispersal and prey capture. According to mechanical characteristics, adhesive secretions on both leaves of the carnivorous flypaper Roridula gorgonias and epizoochorous fruits of Peperomia polystachya were expected to be similar. The chemical analysis of these adhesives turned out to be challenging because of the limited available mass for analysis. Size exclusion chromatography and Fourier transform infrared spectroscopy were suitable methods for the identification of a mixture of compounds, most appropriately containing natural resins based on aliphatic esters and carboxylic acids. The IR spectra of the Peperomia and Roridula adhesive resemble each other; they correspond to that of a synthetic ethylene–vinyl acetate copolymer, but slightly differ from that of natural tree resins. Thus, the pressure sensitive adhesive properties of the plant adhesives are chemically proved. Such adhesives seem to appear independently in distantly related plant lineages, habitats, life forms, as well as plant organs, and serve different functions such as prey capture in Roridula and fruit dispersal in Peperomia. However, more detailed chemical analyses still remain challenging because of the small available volume of plant adhesive.

     

A new plant-animal mutualism involving a plant with sticky leaves and a resident hemipteran insect

We report on a new plant-animal mutualism in which the plant Roridula gorgonias, first suspected by Darwin (1875) to be carnivorous, is, at least in part, indirectly carnivorous. This plant has sticky leaves which trap many insects but it has no digestive enzymes. Instead, trapped invertebrates are rapidly consumed by a hemipteran Pameridea roridulae, only found on this plant. However, evidence from ¹⁵N experiments suggests that R. gorgonias does derive significant amounts of nitrogen from trapped prey, apparently via exudations of P. roridulae.     

Trap closure and prey retention in Venus flytrap (Dionaea muscipula) temporarily reduces photosynthesis and stimulates respiration

Background and Aims

The carnivorous plant Venus flytrap (Dionaea muscipula) produces a rosette of leaves: each leaf is divided into a lower part called the lamina and an upper part, the trap, with sensory trigger hairs on the adaxial surface. The trap catches prey by very rapid closure, within a fraction of a second of the trigger hairs being touched twice. Generation of action potentials plays an important role in closure. Because electrical signals are involved in reduction of the photosynthetic rate in different plant species, we hypothesized that trap closure and subsequent movement of prey in the trap will result in transient downregulation of photosynthesis, thus representing the energetic costs of carnivory associated with an active trapping mechanism, which has not been previously described.

Methods

Traps were enclosed in a gas exchange cuvette and the trigger hairs irritated with thin wire, thus simulating insect capture and retention. Respiration rate was measured in darkness (R_D). In the light, net photosynthetic rate (A_N), stomatal conductance (g_s) and intercellular CO₂ concentration (c_i) were measured, combined with chlorophyll fluorescence imaging. Responses were monitored in the lamina and trap separately.

Key Results

Irritation of trigger hairs resulted in decreased A_N and increased R_D, not only immediately after trap closure but also during the subsequent period when prey retention was simulated in the closed trap. Stomatal conductance remained stable, indicating no stomatal limitation of A_N, so c_i increased. At the same time, the effective quantum yield of photosystem II (Φ_PSII) decreased transiently. The response was confined mainly to the digestive zone of the trap and was not observed in the lamina. Stopping mechanical irritation resulted in recovery of A_N, R_D and Φ_PSII.

Conclusions

We put forward the first experimental evidence for energetic demands and carbon costs during insect trapping and retention in carnivorous plants, providing a new insight into the cost/benefit model of carnivory.     

Murderous plants: Victorian Gothic,Darwin and modern insights into vegetable carnivory

Darwin's interest in carnivorous plants was in keeping with the Victorian fascination with Gothic horrors, and his experiments on them were many and varied, ranging from what appears to be idle curiosity (e.g. what will happen if I place a human hair on a Drosera leaf?) to detailed investigations of mechanisms. Mechanisms for capture and digestion of prey vary greatly among the six (or more) lineages of flowering plants that have well‐developed carnivory, and some are much more active than others. Passive carnivory is common in some groups, and one, Roridula (Roridulaceae) from southern Africa, is so passively carnivorous that it requires the presence of an insect intermediate to derive any benefit from prey trapped on its leaves. Other groups not generally considered to be carnivores, such as Stylidium (Stylidiaceae), some species of Potentilla (Rosaceae), Proboscidea (Martyniaceae) and Geranium (Geraniaceae), that have been demonstrated to both produce digestive enzymes on their epidermal surfaces and be capable of absorbing the products, are putatively just as ‘carnivorous’ as Roridula. There is no clear way to discriminate between cases of passive and active carnivory and between non‐carnivorous and carnivorous plants – all intermediates exist. Here, we document the various angiosperm clades in which carnivory has evolved and the degree to which these plants have become ‘complete carnivores’. We also discuss the problems with definition of the terms used to describe carnivorous plants. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161 , 329–356.     

Ecophysiological observations on Drosophyllum lusitanicum

The carnivorous plant Drosophyllum lusitanicum inhabits heathland and ruderal sites in Portugal, Spain and Morocco. In the literature, various theories have been discussed concerning the ability of Drosophyllum to survive the annual dry period in summer. In August 2004, we examined: (1) the microclimate, (2) soil parameters and (3) the physiological conditions of the plants on two sites in Portugal and Spain. First, during the day, plants are exposed to very high air and soil temperatures and very low air humidity. The climatic extremes are not significantly softened by the population, only the wind speed is drastically decreased. During the night, on the other hand, very high air humidity and dew formation could be observed. The harsh climate is accompanied by stressful soil conditions. Second, the soil is completely dry, poor in fine earth, calcium and nutrients and more or less acid. Third, in spite of these climatic and edaphic extremes, all plants were green, produced trapping mucilage and caught numerous animals. Far from being affected by these conditions, Drosophyllum showed even better growth and reproduction on more extreme sites. We analysed the root system and found living fine roots missing. The osmotic value of the plants is rather low and water storage organs are absent. Therefore we conclude that in summer Drosophyllum is nourished by the dew at night.     

It takes two to tango but three is a tangle: mutualists and cheaters on the carnivorous plant <Emphasis Type="Italic">Roridula</Emphasis>

Roridula dentata is associated with hemipterans, which facilitate nitrogen assimmilation from insects. R. dentata is also associated with spiders and their role in digestion is unknown. We quantify approximately how much nitrogen Roridula assimilates from insects through "indirect digestion." Using '¹⁵N we then determine whether nitrogen absorption from hemipteran insects differs with varying spider densities. In this way, we are able to determine their nutritional role. At low spider densities, indirect digestion of prey accounts for approximately 70% of plant nitrogen. These values are comparable to methods of direct prey digestion found in other carnivorous plants. However spiders decrease the numbers of hemipteran individuals inhabiting Roridula plants and also decrease efficiency of indirect prey digestion by up to 30%. We deduce that spiders are cheaters as they exploit plant rewards without offering any rewards in return. However, indirect carnivory is still efficient enough when hemipteran densities are at their lowest, ensuring that the mutualism does not break down.     

Mineral cost of carnivory in aquatic carnivorous plants

Tissue N, P, K, Ca, and Mg content was estimated in traps and photosynthetic and carnivorous shoots in five aquatic carnivorous plant species from an outdoor culture: Aldrovanda vesiculosa, Utricularia vulgaris, U. reflexa, U. intermedia, and U. stygia, for the determination of the mineral cost of carnivory. In three species with monomorphic shoots (A. vesiculosa, U. vulgaris, U. reflexa), tissue P and K content in traps was significantly higher than that in their photosynthetic shoots, whereas N content was about the same. In U. stygia and U. intermedia with dimorphic shoots, tissue N and P content was markedly the highest in photosynthetic shoots followed by traps, while it was lowest in carnivorous shoots. In all five species, trap K content was significantly (2–4 times) higher than that in photosynthetic and carnivorous shoots. In all species, the values of the mineral cost of carnivory – the proportion of mineral nutrient amount contained in traps or carnivorous shoots to that in the total plant biomass – were within 19–61% for N, 33–76% P, 51–78% K, 26–70% Ca, and 34% for Mg. A new concept of the ecological cost-benefit relationships of plant carnivory, based on the mineral benefit of prey capture and mineral costs associated with trap production, is introduced for aquatic carnivorous plants. The evolution of this plant group is considered to show the optimization of these mineral cost-benefit relationships.     

The Smart Aerial Release Machine,a Universal System for Applying the Sterile Insect Technique

Background

Beyond insecticides, alternative methods to control insect pests for agriculture and vectors of diseases are needed. Management strategies involving the mass-release of living control agents have been developed, including genetic control with sterile insects and biological control with parasitoids, for which aerial release of insects is often required. Aerial release in genetic control programmes often involves the use of chilled sterile insects, which can improve dispersal, survival and competitiveness of sterile males. Currently available means of aerially releasing chilled fruit flies are however insufficiently precise to ensure homogeneous distribution at low release rates and no device is available for tsetse.

Methodology/Principal Findings

Here we present the smart aerial release machine, a new design by the Mubarqui Company, based on the use of vibrating conveyors. The machine is controlled through Bluetooth by a tablet with Android Operating System including a completely automatic guidance and navigation system (MaxNav software). The tablet is also connected to an online relational database facilitating the preparation of flight schedules and automatic storage of flight reports. The new machine was compared with a conveyor release machine in Mexico using two fruit flies species (Anastrepha ludens and Ceratitis capitata) and we obtained better dispersal homogeneity (% of positive traps, p<0.001) for both species and better recapture rates for Anastrepha ludens (p<0.001), especially at low release densities (<1500 per ha). We also demonstrated that the machine can replace paper boxes for aerial release of tsetse in Senegal.

Conclusions/Significance

This technology limits damages to insects and allows a large range of release rates from 10 flies/km² for tsetse flies up to 600 000 flies/km² for fruit flies. The potential of this machine to release other species like mosquitoes is discussed. Plans and operating of the machine are provided to allow its use worldwide.     

Holocentric chromosomes may be an apomorphy of Droseraceae

Holocentric chromosomes have evolved in various plant and animal taxa, which suggests they may confer a selective advantage in certain conditions, yet their adaptive potential has scarcely been studied. One of the reasons may reside in our insufficient knowledge of the phylogenetic distribution of holocentric chromosomes across eukaryotic phylogeny. In the present study, we focused on Droseraceae, a carnivorous plant family with an unknown chromosomal structure in monotypic genera Dionaea and Aldrovanda, and a closely related monotypic family Drosophyllaceae. We used flow cytometry to detect holocentric chromosomes by measuring changes in the ratio of the number of G2 nuclei to the number of G1 nuclei in response to gamma irradiation and determined chromosomal structures in Aldrovanda vesiculosa, Dionaea muscipula, Drosera tokaiensis, and Drosera ultramafica from Droseraceae and Drosophyllum lusitanicum from Drosophyllaceae. We confirmed monocentric chromosomes in D. lusitanicum and detected holocentric chromosomes in all four Droseraceae. Our novel finding of holocentric chromosomes in monotypic genera Aldrovanda and Dionaea suggests that all Droseraceae may be holocentric, but to confirm that further research is needed due to previously reported conflicting results in Drosera rotundifolia.     

Chromosome size and DNA values in sundews (Droseraceae)

Relative DNA content has been determined Feulgen cytophotometrically and autoradiographically for roottip nuclei of Drosophyllum lusitanicum L., (2n=12), Drosera rotundifolia L. (2x=20), D. intermedia Hayne (2x=20), D. linearis Goldie (2x= 20), D. binata Labill. (3x=32), D. capensis L. (4x= 40), D. spathulata Labill. (8x=80), all Droseraceae. Relative DNA values per diploid genome for Drosophyllum and diploid, triploid, and higher polyploid Drosera were approximately as 16421. These values are terms of a geometric series and are compatible with a multistranded (polyneme) interpretation of chromosome structure.     

GLANDULAR LEAF STRUCTURE OF TRIPHYOPHYLLUM PELTATUM (DIONCOPHYLLACEAE): A “FLY-PAPER” INSECT TRAPPER

Certain leaves of Triphyophyllum peltatum (Hutch. & Dalz.) Airy Shaw (Dioncophyllaceae) have an extended, erect midrib covered with stalked and sessile glands exhibiting insect-trapping ability. The stalked glands secrete a sticky, acid mucilage to which numerous insects in various stages of decay were observed adhering. The morphology and anatomy of the glandular leaves were investigated with light and scanning electron microscopy. The midrib and the lamina in the lowermost part of the leaf bear stomata. Those of the midrib are transitional between actinocytic and cyclocytic in type. Parenchyma cells in mature and immature portions of the midrib and in the glands contain numerous crystals and amyloplasts. The anatomy of the stalked and sessile glands is remarkably similar to that of Drosophyllum lusitanicum (L.) Link. (Droseraceae). A distinct cuticle covers the gland head, but no pores are visible. Three distinct layers underlie the cuticle: a definite epidermal layer with irregularly thickened cell walls, and two layers of more loosely arranged cells. A fourth layer, endodermoid in nature with radially thickened cell walls, connects the head and stalk of the stalked glands and the head and midrib parenchyma of the sessile glands. Vascular elements (including helical and scalariform tracheary elements) reach the endodermoid layer. According to recent studies, Triphyophyllum and Drosophyllum have different phylogenetic origins; the morphological and anatomical similarities in the insect-trapping glandular leaves show more support for their convergent evolution rather than for an alliance of the Dioncophyllaceae with the Droseraceae.     

Wolbachia infection decreased the resistance of Drosophila to lead

Background

The heavy metal lead has been shown to be associated with a genotoxic risk. Drosophila melanogaster is a model organism commonly utilized in genetic toxicology testing. The endosymbionts — Wolbachia are now very common in both wild populations and laboratory stocks of Drosophila. Wolbachia may induce resistance to pathogenic viruses, filarial nematodes and Plasmodium in fruit fly and mosquito hosts. However the effect of Wolbachia infection on the resistance of their hosts to heavy metal is unknown.

Methodology/Principal Findings

Manipulating the lead content in the diet of Drosophila melanogaster, we found that lead consumption had no different effects on developmental time between Wolbachia-infected (Dmel wMel) and –uninfected (Dmel T) flies. While in Pb-contaminated medium, significantly reduced amount of pupae and adults of Dmel wMel were emerged, and Dmel wMel adults had significantly shorter longevity than that of Dmel T flies. Lead infusion in diet resulted in significantly decreased superoxide dismutase (SOD) activity in Dmel T flies (P<0.05), but not in Dmel wMel flies. Correspondingly, lead cultures induced a 10.8 fold increase in malonaldehyde (MDA) contents in Dmel T larvae (P<0.05). While in Dmel wMel larvae, it resulted in only a 1.3 fold increase. By quantitative RT-PCR, we showed that lead infused medium caused significantly increased expression level of relish and CecA2 genes in Dmel T flies (P<0.01). Lead cultures did not change dramatically the expression of these genes in Dmel wMel flies.

Conclusions/Significance

These results suggest that Wolbachia infection decreased the resistance of Drosophila to lead likely by limiting the production of peroxides resulted from lead, thus being unable to activate the immunological pathway in the host to prevent them from lead damage. This represents a novel Wolbachia–host interaction and provides information that researchers working on Drosophila toxicology should take in consideration the presence of Wolbachia in the stocks they are analyzing.     

Effect of a Standardised Dietary Restriction Protocol on Multiple Laboratory Strains of Drosophila melanogaster

Background

Outcomes of lifespan studies in model organisms are particularly susceptible to variations in technical procedures. This is especially true of dietary restriction, which is implemented in many different ways among laboratories.

Principal Findings

In this study, we have examined the effect of laboratory stock maintenance, genotype differences and microbial infection on the ability of dietary restriction (DR) to extend life in the fruit fly Drosophila melanogaster. None of these factors block the DR effect.

Conclusions

These data lend support to the idea that nutrient restriction genuinely extends lifespan in flies, and that any mechanistic discoveries made with this model are of potential relevance to the determinants of lifespan in other organisms.     

Foliar Mn accumulation in eastern Australian herbarium specimens: prospecting for ��new�� Mn hyperaccumulators and potential applications in taxonomy

Background and Aims

The analysis of herbarium specimens has previously been used to prospect for ‘new’ hyperaccumulators, while the use of foliar manganese (Mn) concentrations as a taxonomic tool has been suggested. On the basis of their geographic and taxonomic affiliations to known Mn hyperaccumulators, six eastern Australian genera from the Queensland Herbarium collection were sampled for leaf tissue analyses.

Methods

ICP-OES was used to measure Mn and other elemental concentrations in 47 species within the genera Austromyrtus, Lenwebbia, Gossia (Myrtaceae), Macadamia (Proteaceae), Maytenus and Denhamia (Celastraceae).

Key Results

The resulting data demonstrated (a) up to seven ‘new’ Mn hyperaccumulators, mostly tropical rainforest species; (b) that one of these ‘new’ Mn hyperaccumulators also had notably elevated foliar Ni concentrations; (c) evidence of an interrelationship between foliar Mn and Al uptake among the Macadamias; (d) considerable variability of Mn hyperaccumulation within Gossia; and (e) the possibility that Maytenus cunninghamii may include subspecies.

Conclusions

Gossia bamagensis, G. fragrantissima, G. sankowsiorum, G. gonoclada and Maytenus cunninghamii were identified as ‘new’ Mn hyperaccumulators, while Gossia lucida and G. shepherdii are possible ‘new’ Mn hyperaccumulators. Of the three Myrtaceae genera examined, Mn hyperaccumulation appears restricted to Gossia, supporting its recent taxonomic revision. In the context of this present investigation and existing information, a reassesment of the general definition of Mn hyperaccumulation may be warranted. Morphological variation of Maytenus cunninghamii at two extremities was consistent with variation in Mn accumulation, indicating two possible ‘new’ subspecies. Although caution should be exercised in interpreting the data, surveying herbarium specimens by chemical analysis has provided an effective means of assessing foliar Mn accumulation. These findings should be followed up by field studies.Key words: Gossia bamagensis, G. fragrantissima, G. sankowskiorum, G. gonoclada, G. lucida, G. shepherdii, Maytenus cunninghamii, Mn hyperaccumulator     

Insecticide susceptibility of Phlebotomus argentipes in visceral leishmaniasis endemic districts in India and Nepal

Objectives

To investigate the DDT and deltamethrin susceptibility of Phlebotomus argentipes, the vector of Leishmania donovani, responsible for visceral leishmaniasis (VL), in two countries (India and Nepal) with different histories of insecticide exposure.

Methods

Standard WHO testing procedures were applied using 4% DDT and 0.05% deltamethrin impregnated papers. The effect of the physiological status (fed and unfed) of females on the outcome of the bioassays was assessed and the optimal time of exposure for deltamethrin was evaluated on a colony population. Field populations from both countries were tested.

Results

Fed and unfed females responded in a similar way. For exposure time on field samples 60 min was adopted for both DDT and deltamethrin. In Bihar, knockdown and mortality with DDT was respectively 20 and 43%. In Nepal almost all sand flies were killed, except at the border with Bihar (mortality 62%). With 0.05% deltamethrin, between 96 and 100% of the sand flies were killed in both regions.

Conclusions

Based on literature and present data 4% DDT and 0.05% deltamethrin seem to be acceptable discriminating concentrations to separate resistant from susceptible populations. Resistance to DDT was confirmed in Bihar and in a border village of Nepal, but the sand flies were still susceptible in villages more inside Nepal where only synthetic pyrethroids are used for indoor spraying. The low effectiveness of indoor spraying with DDT in Bihar to control VL can be partially explained by this resistance hence other classes of insecticides should be tested. In both countries P. argentipes sand flies were susceptible to deltamethrin.