Ants provide nutritional and defensive benefits to the carnivorous plant Sarracenia minor

Ants can have important, but sometimes unexpected, effects on the plants they associate with. For carnivorous plants, associating with ants may provide defensive benefits in addition to nutritional ones. We examined the effects of increased ant visitation and exclusion of insect prey from pitchers of the hooded pitcher plant Sarracenia minor, which has been hypothesized to be an ant specialist. Visitation by ants was increased by placing PVC pipes in the ground immediately adjacent to 16 of 32 pitcher plants, which created nesting/refuge sites. Insects were excluded from all pitchers of 16 of the plants by occluding the pitchers with cotton. Treatments were applied in a 2 × 2 factorial design in order to isolate the hypothesized defensive benefits from nutritional ones. We recorded visitation by ants, the mean number of ants captured, foliar nitrogen content, plant growth and size, and levels of herbivory by the pitcher plant mining moth Exyra semicrocea. Changes in ant visitation and prey capture significantly affected nitrogen content, plant height, and the number of pitchers per plant. Increased ant visitation independent of prey capture reduced herbivory and pitcher mortality, and increased the number of pitchers per plant. Results from this study show that the hooded pitcher plant derives a double benefit from attracting potential prey that are also capable of providing defense against herbivory.     

Effect of light environment on intra-specific variation in herbivory in the carnivorous plant Pinguicula moranensis (Lentibulariaceae)

Identifying the factors that affect a plant’s probability of being found and damaged by herbivores has been a central topic in the study of herbivory. Although herbivory could have important negative consequences on carnivorous plants, their interaction with herbivores remains largely unexplored. We evaluated the effect of spatial variation in light environment (sunny, shade and full-shade sites) on the pattern of leaf herbivory and florivory of the carnivorous plant Pinguicula moranensis. Plants’ overall probability of leaf damage was high (74.24%). Mean herbivory was four times higher in the sunny and shade sites than the observed in the full-shade site. Nearly 8% of plants suffered damage to reproductive structures, although the probability of florivory was similar among sites. Discussion addressed the inter-site variation in mean herbivory considering the effect of light exposure and the impact that herbivory could have on fitness components of this carnivorous plant.     

Evolving Darwin's 'most wonderful' plant: ecological steps to a snap-trap

Among carnivorous plants, Darwin was particularly fascinated by the speed and sensitivity of snap-traps in Dionaea and Aldrovanda . Recent molecular work confirms Darwin's conjecture that these monotypic taxa are sister to Drosera , meaning that snap-traps evolved from a 'flypaper' trap. Transitions include tentacles being modified into trigger hairs and marginal 'teeth', the loss of sticky tentacles, depressed digestive glands, and rapid leaf movement. Pre-adaptations are known for all these traits in Drosera yet snap-traps only evolved once. We hypothesize that selection to catch and retain large insects favored the evolution of elongate leaves and snap-tentacles in Drosera and snap-traps. Although sticky traps efficiently capture small prey, they allow larger prey to escape and may lose nutrients. Dionaea 's snap-trap efficiently captures and processes larger prey providing higher, but variable, rewards. We develop a size-selective model and parametrize it with field data to demonstrate how selection to capture larger prey strongly favors snap-traps. As prey become larger, they also become rarer and gain the power to rip leaves, causing returns to larger snap-traps to plateau. We propose testing these hypotheses with specific field data and Darwin-like experiments. The complexity of snap-traps, competition with pitfall traps, and their association with ephemeral habitats all help to explain why this curious adaptation only evolved once.     

Defense and carnivory: Dual role of bracts inPassiflora foetida

Members of the genusPassiflora are reported to have evolved modifications which kill insects; they have however never been tested for carnivorous syndrome. The flowers ofPassiflora foetida consists of highly reticulate bracts which cover and grow along with the buds and fruits. Removal of bracts from developing bud and fruit resulted in higher predatory damage compared to those where the bracts were intact. These bracts also possess a large number of minute glands which ooze sticky secretion. A variety of tiny insects were found trapped by the secretion of the bracts. The secretion of these glands show high proteases and acid phosphatase activity, two common digestive enzymes found in traps of true carnivorous plants. A high quantity of aminoacids were released from freshly freeze killed ants when incubated in buffer extract of bracts-[¹⁴C] phenylalanine smeared on the glandular surface of bracts was recovered from ovules suggesting potential for absorption of aminoacids. These results suggest a novel role for bracts where primary function is to minimize predatory damage to developing flowers and fruits. The bracts serve as insect traps and also possess the mechanism to digest the trapped insects to obtain free aminoacids.     

Sticky plant captures prey for symbiotic bug: is this digestive mutualism?

Many plants capture and kill insects but, until relatively recently, only carnivorous plants with digestive enzymes were known to gain directly from the nutrients of those insects. Recent studies show that some carnivorous plants lack digestive enzymes and have evolved digestive mutualisms with symbiotic insects that digest their prey for them. Rhododendron macrosepalum, a plant with sticky leaves that captures insects, has an association with symbiotic Mirid bugs that consume the insects captured. Here, we determine what the nature of the relationship is between Mirid and plant. We find that R. macrosepalum has no digestive enzymes of its own but that it does not seem to have the ability to absorb hemipteran faeces through its leaf cuticle. Naturally occurring levels of ¹⁵N and ¹⁴N were used to determine that R. macrosepalum gains no nitrogen through its association with the Mirid bugs and that it obtains all of its nitrogen from the soil. The Mirids, on the other hand, seem to obtain nitrogen from insects captured by the plant, as well as from plant tissues. The relationship between plant and Mirid is not a digestive mutualism but more likely an antagonistic relationship. This study adds to our understanding of how digestive mutualisms evolve and shows that insect capture alone, or in combination with a symbiotic insect relationship does not necessarily make a plant ‘carnivorous’.     

Energetics and the evolution of carnivorous plants--Darwin's 'most wonderful plants in the world'

Carnivory has evolved independently at least six times in fiveangiosperm orders. In spite of these independent origins, thereis a remarkable morphological convergence of carnivorous planttraps and physiological convergence of mechanisms for digestingand assimilating prey. These convergent traits have made carnivorousplants model systems for addressing questions in plant moleculargenetics, physiology, and evolutionary ecology. New data showthat carnivorous plant genera with morphologically complex trapshave higher relative rates of gene substitutions than do thosewith simple sticky traps. This observation suggests two alternativemechanisms for the evolution and diversification of carnivorousplant lineages. The ‘energetics hypothesis’ positsrapid morphological evolution resulting from a few changes inregulatory genes responsible for meeting the high energeticdemands of active traps. The ‘predictable prey capturehypothesis’ further posits that complex traps yield morepredictable and frequent prey captures. To evaluate these hypotheses,available data on the tempo and mode of carnivorous plant evolutionwere reviewed; patterns of prey capture by carnivorous plantswere analysed; and the energetic costs and benefits of botanicalcarnivory were re-evaluated. Collectively, the data are moresupportive of the energetics hypothesis than the predictableprey capture hypothesis. The energetics hypothesis is consistentwith a phenomenological cost–benefit model for the evolutionof botanical carnivory, and also accounts for data suggestingthat carnivorous plants have leaf construction costs and scalingrelationships among leaf traits that are substantially differentfrom those of non-carnivorous plants. Key words: Carnivorous plants, competition, construction costs, cost–benefit model, Darwin, energetics, niche overlap, phylogeny, prey capture, universal spectrum of leaf traits Received 6 May 2008; Revised 5 June 2008 Accepted 16 June 2008     

Trichomes as sensors: Detecting activity on the leaf surface

The dramatic movements of some carnivorous plants species are triggered by sensory structures derived from trichomes. While unusual plant species such as the Venus fly trap and sundews may be expected to have elaborate sensors to capture their insect prey, more modest plant species might not be expected to have similar sensory capabilities. Our recent work, however, has revealed that glandular trichomes on tomato (Solanum lycopersicum) appear to have a function similar to trigger hairs of carnivorous species, acting as “early warning” sensors. Using a combination of behavioral, molecular, and biochemical techniques, we determined that caterpillars, moths and mechanical disruption upregulate signaling molecules and defensive genes found in glandular trichomes. Importantly, we discovered that plants whose trichomes have been broken respond more vigorously when their defenses were induced. Taken together, our results suggest that glandular trichomes can act as sensors that detect activity on the leaf surface, and ready plants for herbivore attack.Key words: glandular trichome, induced responses, jasmonic acid, plant-insect interactions, sensor, Solanum lycopersicum, tomatoCertain plant species are renowned for their ability to respond to contact. The Venus fly trap (Dionaea muscipula) and sundew (Drosera) species come to mind quickly as obviously thigmotropic species. When an insect lands on these carnivorous plant species, dramatic movements ensue once the prey is detected. Some Drosera species respond to contact by bending their “tentacles” toward their trapped prey to further ensnare the victim and begin the process of digestion. These dramatic plant species have captured the attention of many scientists, including Darwin, who remarked on the “extraordinary sensitiveness of [their] glands to slight pressure” and surmised that the tentacles of sundew plants “existed primordially as glandular hairs.”¹ As is often the case, Darwin appears to have been quite right. Indeed, morphological and molecular work supports the notion that sundew tentacles and the trigger hairs of the Venus fly trap are homologous sensory structures likely derived from trichomes.^2,3Given Darwin’s appreciation of these trichome-derived sensory organs, he perhaps would not have been surprised by mounting evidence that suggests that trichomes may play even a broader sensory role for plants. We have recently found evidence that glandular trichomes can act as early detection sensors for some plant species.⁴ These trichomes can be disrupted by the footsteps of walking moths and caterpillars (and other forms of light touching), and this apparently minor plant damage leads to a state of defensive readiness that allows plants to respond to herbivory more quickly than undamaged plants. While this level of trichome-mediated detection does not result in the conspicuous responses of some carnivorous plant species, it still results in significant physiological changes that prepare plants for attack.In our recent effort, we worked with tomato (Solanum lycopersicum), using a combination of behavioral, molecular, and biochemical techniques to understand the role of trichomes in detecting activity on the leaf surface.⁴ Defense signaling has been well studied in tomato and there exists a variety of mutants whose defensive responses have been compromised. Moreover, it has been known that tomatoes have a variety of trichome types, including two types of glandular trichomes that burst upon contact with insects, releasing their cellular contents and physically impeding insects (Fig. 1).^5,6Open in a separate windowFigure 1Surface of a tomato leaf showing (A) intact rounded heads of glandular trichomes (black arrows) and (B) trichomes disrupted with a gloved hand (absence of rounded heads except for a few in the upper left corner [black arrows]). Images were captured at 36x magnification and were taken from different parts of the same leaf.To determine if plant defense pathways were induced by insect contact, we allowed three species of caterpillar (Manduca sexta, Heliothis virescens and Helicoverpa zea) and one species of moth (H. zea) to crawl over tomato leaves for ten minutes. As a positive control, we also lightly rubbed leaves with a gloved hand or a metal rod. Within time frames ranging from three to twenty-four hours all treatments, insect and otherwise, significantly induced defensive genes as measured by qRT-PCR. Using a combination of RT-PCR and in situ hybridization, we confirmed that JA-signaling and defensive genes are expressed in trichomes. A GC-MS-based technique then confirmed that JA was present in trichomes of undamaged plants and DAB staining, in combination with catalase treatment, provided evidence that hydrogren peroxide and JA are key signals mediating defensegene induction. These conclusions were further reinforced by experiments with def1 mutants, a line of tomato impaired in JA signaling, and accession LA3610, a tomato variety with reduced numbers of trichomes. Lastly, we conducted a factorial experiment both disrupting trichomes and treating tomato plants with methyl jasmonate (MeJA), which induces plant defenses and increases densities of trichomes.⁷ Results of this final experiment indicated that plants that received both treatments (i.e., MeJA and disruption) had greater defensive gene induction than plants that were only treated with MeJA or plants whose trichomes remained intact, suggesting that increases in trichomes may contribute to greater sensitivity to touch-induced responses.Taken together, our results are highly suggestive that trichomes can act as “early warning” detectors for plants. Moths seeking to lay eggs on tomato are likely to break trichomes as they explore leaves, upregulating plant defenses in anticipation of egg hatch and feeding by neonate caterpillars. Similarly, herbivores colonizing a new host plant and breaking trichomes on their way across a leaf also appear to “tip the plant off” to impending attack. Considering the drastic response of carnivorous plants to touch, perhaps it should not be surprising that trichomes can function more broadly as sensors. In an evolutionary context, it seems logical that trichomes took on this role. For many plant species, “hairy” varieties receive less herbivory,⁸ so within a population there could have been a fitness advantage in having more trichomes. Once established, this hairy phenotype could then have been refined via mutation and selection for trichome varieties that had functions adaptive for the plant, perhaps driving the evolution of glandular trichomes and their role as sensors.Granted, the generalized nature of our results would appear to indicate that plants could be “primed” by nearly any arthropod species that crosses one of their leaves. This would, of course, include natural enemies, which are capable of decreasing herbivore pressure and improving plant fitness.^9,10 However, it has been hypothesized that priming evolved due to high fitness costs associated with defensive induction following threats of only minor severity.¹¹ Priming provides an advantage by settling plants into an intermediate “ready” state that allows them to deploy strong defense responses more quickly and the fitness cost associated with being “primed” are lower than full defensive induction.¹² Presumably, fitness costs following priming due to natural enemyinduced trichome disruption would also be less than the cost incurred from a bout of unanticipated herbivory and, over the life of the plant, it would be worth the effort to prepare for attack even if the perceived risk is from a natural enemy and not a foe.Our results build on previously reported priming mechanisms that prepare plants for attack.^13,14 And they reveal an additional level of sophistication in the sensory capabilities of plants, which have already been shown to be able to detect nearby threats of herbivory and increase their defenses in response.^15,16 It seems that trichomes may have played a much wider role in shaping the nature of plant-animal interaction than previously recognized and we look forward to further work elaborating their function.     

Three carnivorous plant species (Drosera spp.) in European Russia: peaceful coexistence?

In spite of the recent improvements in the understanding of carnivorous plants’ biology, some questions have remained unanswered. In this study, the segregation of food niches (i.e. specialization on different categories of prey) for three sympatric carnivorous temperate Drosera species with different shapes of trapping leaves is tested. Potentially available prey was also taken into account, by using artificial traps. Almost all the prey trapped by the three Drosera species and by passive traps belonged to four insect orders: Diptera, Hymenoptera, Coleoptera, Homoptera, as well as Araneae. Diptera specimens were the main prey for all the species. This study demonstrates that arthropods caught by the three temperate sympatric sundew species (D. rotundifolia, D. obovata and D. anglica), belong to the same orders. The proportions of prey from different orders, caught by different sundew species did not differ significantly. The result does not necessarily imply the absence of interspecific competition for prey: arthropods were identified only to order, and competition may have resulted in specialization on prey taxa of lower rank.     

Explaining differential herbivory in sun and shade: the case of Aristotelia chilensis saplings

Differential herbivory in contrasting environments is commonly explained by differences in plant traits. When several plant traits are considered, separate correlation analyses between herbivory and candidate traits are typically conducted. This makes it difficult to discern which trait best explain the herbivory patterns, or to avoid spurious inferences due to correlated characters. Aristotelia chilensis saplings sustain greater herbivory in shaded environments than in open habitats. We measured alkaloids, phenolics, trichomes, leaf thickness and water content in the same plants sampled for herbivory. We conducted a multiple regression analysis to estimate the relationship between herbivory and each plant trait accounting for the effect of correlated traits, thus identifying which trait(s) better explain(s) the differential herbivory on A. chilensis. We also estimated insect abundance in both light environments. Palatability bioassays tested whether leaf consumption by the main herbivore on A. chilensis was consistent with field herbivory patterns. Overall insect abundance was similar in open and shaded environments. While saplings in open environments had thicker leaves, lower leaf water content, and higher concentration of alkaloids and phenolics, no difference in trichome density was detected. The multiple regression analysis showed that leaf thickness was the only trait significantly associated with herbivory. Thicker leaves received less damage by herbivores. Sawfly larvae consumed more leaf tissue when fed on shade leaves. This result is consistent with field herbivory and, together with results of insect abundance, renders unlikely that the differential herbivory in A. chilensis was due to greater herbivory pressure in open habitats.     

Pollinator‐prey conflict in carnivorous plants

Most carnivorous plants utilize insects in two ways: the flowers attract insects as pollen vectors for sexual reproduction, and the leaves trap insects for nutrients. Feeding on insects has been explained as an adaptation to nutrient‐poor soil, and carnivorous plants have been shown to benefit from insect capture through increased growth, earlier flowering and increased seed production. Most carnivorous plant species seem to benefit from insect pollination, although many species autonomously self‐pollinate and some propagate vegetatively. However, assuming that outcross pollen is advantageous and is a more important determinant of reproductive success than the nutrients gained from prey, there should be a selective pressure on carnivorous plants not to feed on their potential pollen vectors. Therefore, it has been suggested that carnivorous plants are subject to a conflict, often called the pollinator‐prey conflict (PPC). The conflict results from a trade‐off of the benefits from feeding on potentially pollinating insects versus the need to use them as pollen vectors for sexual reproduction. In this review we analyze the conditions under which a PPC may occur, review the evidence for the existence of PPCs in carnivorous plants, and explore the mechanisms that may be in place to prevent or alleviate a PPC. With respect to the latter, we discuss how plant signals such as olfactory and visual cues may play a role in separating the functions of pollinator attraction and prey capture.     

Fluorescent prey traps in carnivorous plants

Carnivorous plants acquire most of their nutrients by capturing ants, insects and other arthropods through their leaf‐evolved biological traps. So far, the best‐known attractants in carnivorous prey traps are nectar, colour and olfactory cues. Here, fresh prey traps of 14 Nepenthes, five Sarracenia, five Drosera, two Pinguicula species/hybrids, Dionaea muscipula and Utricularia stellaris were scanned at UV 366 nm. Fluorescence emissions of major isolates of fresh Nepenthes khasiana pitcher peristomes were recorded at an excitation wavelength of 366 nm. N. khasiana field pitcher peristomes were masked by its slippery zone extract, and prey capture rates were compared with control pitchers. We found the existence of distinct blue fluorescence emissions at the capture spots of Nepenthes, Sarracenia and Dionaea prey traps at UV 366 nm. These alluring blue emissions gradually developed with the growth of the prey traps and diminished towards their death. On excitation at 366 nm, N. khasiana peristome 3:1 CHCl₃–MeOH extract and its two major blue bands showed strong fluorescence emissions at 430–480 nm. Masking of blue emissions on peristomes drastically reduced prey capture in N. khasiana pitchers. We propose these molecular emissions as a critical factor attracting arthropods and other visitors to these carnivorous traps. Drosera, Pinguicula and Utricularia prey traps showed only red chlorophyll emissions at 366 nm.     

南美斑潜蝇为害对黄瓜体内4种防御酶活性的影响

植物对昆虫取食产生的防御反应,在昆虫与植物相互作用关系中起着重要的作用。为明确南美斑潜蝇Liriomyza huidobrensis(Blanchard)取食与植物防御之间的作用关系,本文分别测定了南美斑潜蝇幼虫持续为害1、3、5、7及9d后黄瓜叶片中苯丙氨酸解氨酶(PAL)、多酚氧化酶(PPO)、过氧化物酶(POD)及超氧化物歧化酶(SOD)活性的变化。结果表明：在南美斑潜蝇幼虫持续取食下,PAL、PPO、POD和SOD等4种酶活性显著上升;PAL、PPO和POD等3种酶活性随受害程度的加重而上升幅度加大,即重度受害>轻度受害>系统对照>健康对照,而SOD活性变化没有规律。在系统对照黄瓜叶片中,PAL、PPO、POD和SOD等4种酶活性最大值分别在第5、1、5和5d;在轻度受害黄瓜叶片中,PAL、PPO、POD和SOD等4种酶活性最大值分别在第5、9、5和9d;在重度受害黄瓜叶片中,PAL、PPO、POD和SOD等4种酶活性最大值分别在第7、7、5和5d。黄瓜叶片受害后,POD和PPO活性上升幅度较大,PAL和SOD活性上升幅度较小,说明POD和PPO对取食胁迫响应比PAL和SOD更灵敏。     

Red trap colour of the carnivorous plant Drosera rotundifolia does not serve a prey attraction or camouflage function

The traps of many carnivorous plants are red in colour. This has been widely hypothesized to serve a prey attraction function; colour has also been hypothesized to function as camouflage, preventing prey avoidance. We tested these two hypotheses in situ for the carnivorous plant Drosera rotundifolia. We conducted three separate studies: (i) prey attraction to artificial traps to isolate the influence of colour; (ii) prey attraction to artificial traps on artificial backgrounds to control the degree of contrast and (iii) observation of prey capture by D. rotundifolia to determine the effects of colour on prey capture. Prey were not attracted to green traps and were deterred from red traps. There was no evidence that camouflaged traps caught more prey. For D. rotundifolia, there was a relationship between trap colour and prey capture. However, trap colour may be confounded with other leaf traits. Thus, we conclude that for D. rotundifolia, red trap colour does not serve a prey attraction or camouflage function.     

Do carnivorous plants use volatiles for attracting prey insects?

1.  Scientists have been fascinated by carnivorous plants for centuries and they have thoroughly investigated how these plants can benefit from insect capture for example through increased growth, earlier flowering, and increased seed production. How prey is actually lured into the traps, however, is less well understood. Trapping prey may be achieved in a random way, for example by camouflaging the traps (hiding them in the surrounding vegetation), so that prey is trapped by accidental landing on the trap leaves or wind drift, or in the other extreme, trapping may involve mimicry of other attractive resources such as fruits or flowers by using specific visual or olfactory signals to attract a specific prey assemblage.
2.  We investigated for the first time volatiles of the trapping leaves of carnivorous plant species by dynamic headspace methods. We present data on the venus flytrap Dionaea muscipula , the sundew Drosera binata , and the North American pitcher plants Sarracenia flava , Sarracenia leucophylla , Sarracenia minor , and Sarracenia purpurea . A large number of compounds and relatively high emission rates were found in three of the North American pitcher plants ( S. flava , S. leucophylla , and S. minor ) with compounds typically found in flowers or fruits. This suggests together with other features (e.g. colour, nectar production) that these traps are possibly flower or fruit mimics. The leaves of S. purpurea , Dionaea muscipula , and Drosera binata emitted much weaker scents with lower numbers of components, consisting mainly of volatiles typically emitted from green leaves.
3.  We discuss whether or not the use of volatiles for attracting prey animals is linked with specific trapping mechanisms and whether carnivorous plants can be grouped into specialized 'olfactory syndromes'.     

Glandular trichomes as an inflorescence defence mechanism against insect herbivores in Iberian columbines

Glandular trichomes play a defensive role against herbivores in the leaves of many plant species. However, their functional role in inflorescences has not been studied, even though theory suggests that tissues with a higher fitness value, such as inflorescences, should be better defended. Using manipulative experiments, we analysed the defensive role of glandular trichomes against herbivorous insects in the inflorescence of Iberian columbines (genus Aquilegia), and its inter-population and inter-taxa variation in relation to herbivore abundance and potential selective pressure. The experiments were conducted in eight populations belonging to four subspecies of two columbines (Aquilegia vulgaris and Aquilegia pyrenaica). For each population, we estimated the density of glandular trichomes in the inflorescences, the abundance of insects stuck in the inflorescences, the abundance of small herbivorous insects, the incidence of damage on flowers and fruits, and the fruit set. The density of glandular trichomes on the inflorescence of A. vulgaris and A. pyrenaica was higher in regions of higher herbivore abundance. We also found that when the plants lose the protection of glandular trichomes, small insects have better access to flowers and fruits, causing more damage and reducing plant fitness. This study concludes that glandular trichomes are part of an adaptive response against phytophagous insect herbivory. The observed variation in herbivore pressure between taxa, likely caused by habitat differentiation, might have played a role in trait differentiation through divergent selection. This result adds evidence to the differentiation of the Iberian columbines through habitat specialization.     

Molecular and functional evolution of class I chitinases for plant carnivory in the caryophyllales

Proteins produced by the large and diverse chitinase gene family are involved in the hydrolyzation of glycosidic bonds in chitin, a polymer of N-acetylglucosamines. In flowering plants, class I chitinases are important pathogenesis-related proteins, functioning in the determent of herbivory and pathogen attack by acting on insect exoskeletons and fungal cell walls. Within the carnivorous plants, two subclasses of class I chitinases have been identified to play a role in the digestion of prey. Members of these two subclasses, depending on the presence or absence of a C-terminal extension, can be secreted from specialized digestive glands found within the morphologically diverse traps that develop from carnivorous plant leaves. The degree of homology among carnivorous plant class I chitinases and the method by which these enzymes have been adapted for the carnivorous habit has yet to be elucidated. This study focuses on understanding the evolution of carnivory and chitinase genes in one of the major groups of plants that has evolved the carnivorous habit: the Caryophyllales. We recover novel class I chitinase homologs from species of genera Ancistrocladus, Dionaea, Drosera, Nepenthes, and Triphyophyllum, while also confirming the presence of two subclasses of class I chitinases based upon sequence homology and phylogenetic affinity to class I chitinases available from sequenced angiosperm genomes. We further detect residues under positive selection and reveal substitutions specific to carnivorous plant class I chitinases. These substitutions may confer functional differences as indicated by protein structure homology modeling.     

Quantification of insect nitrogen utilization by the venus fly trap Dionaea muscipula catching prey with highly variable isotope signatures.

Dionaea is a highly specialized carnivorous plant species with a unique mechanism for insect capture. The leaf is converted into an osmotically driven trap that closes when an insect triggers sensory trichomes. This study investigates the significance of insect capture for growth of Dionaea at different successional stages after a fire, under conditions where the prey is highly variable in its isotope signature. The contribution of insect-derived nitrogen (N) was estimated using the natural abundance of 15N. In contrast to previous 15N studies on carnivorous plants, the problem emerges that delta15N values of prey insects ranged between -4.47 per thousand (grasshoppers) and +7.21 per thousand (ants), a range that exceeds the delta15N values of non carnivorous reference plants (-4.2 per thousand) and soils (+3 per thousand). Thus, the isotope-mixing model used by Shearer and Kohl to estimate the amount of insect-derived N is not applicable. In a novel approach, the relationships of delta15N values of different organs with delta15N of trapping leaves were used to estimate N partitioning within the plant. It is estimated that soon after fire approximately 75% of the nitrogen is obtained from insects, regardless of plant size or developmental stage. The estimates are verified by calculating the average isotope signatures of insects from an isotope mass balance and comparing this with the average measured delta15N values of insects. It appears that for Dionaea to survive and reach the flowering stage, seedlings must first reach the 6th-leaf rosette stage, in which trap surface area nearly doubles and facilitates the capture of large insects. Large amounts of nitrogen thus made available to plants may facilitate an enhanced growth rate and the progressive production of additional large traps. Dionaea reaches a maximum abundance after fire when growth of the competing vegetation is suppressed. About 10 years after fire, when grasses and shrubs recover, Dionaea becomes overtopped by other species. This would not only reduce carbon assimilation but also the probability of catching larger prey. The amount of insect-derived nitrogen decreases to 46%, and Dionaea becomes increasingly dependent on N-supply from the soil. Competition for both light and N may cause the near disappearance of Dionaea in older stages of the fire succession.     

Plant glandular trichomes mediate protective mutualism in a spider–plant system

1. Although several species of Peucetia (Oxyopidae) live strictly in association with plants bearing glandular trichomes worldwide, to date little is known about whether these associations are mutualistic. 2. In this study we manipulated the presence of Peucetia flava on the glandular plant Rhynchanthera dichotoma in the rainy and post‐rain season, to test the strength of its effects on leaf, bud, and flower damage and plant reproductive output. In addition, we ran independent field experiments to examine whether these sticky structures improve spider fidelity to plants. 3. Peucetia suppressed some species of foliar phytophages, but not others. Although spiders have reduced levels of leaf herbivory, this phenomenon was temporally conditional, i.e. occurred only in the post‐rain but not in the rainy season. Floral herbivory was also reduced in the presence of spiders, but these predators did not affect plant fitness components. 4. Plants that had their glandular trichomes removed retained fewer insects than those bearing such structures. Spiders remained longer on plants with glandular trichomes than on plants in which these structures had been removed. Isotopic analyses showed that spiders that fed on live and dead labelled flies adhered to the glandular hairs in similar proportions. 5. Spiders incurred no costs to the plants, but can potentially increase individual plant fitness by reducing damage to reproductive tissues. Temporal conditionality probably occurred because plant productivity exceeded herbivore consumption, thus dampening top‐down effects. Specialisation to live on glandular plants may have favoured scavenging behaviour in Peucetia, possibly an adaptation to periods of food scarcity.     

Tentacles of in vitro-grown round-leaf sundew (<Emphasis Type="Italic">Drosera rotundifolia</Emphasis>L.) show induction of chitinase activity upon mimicking the presence of prey

Induction of plant-derived chitinases in the leaves of a carnivorous plant was demonstrated using aseptically grown round-leaf sundew (Drosera rotundifolia L.). The presence of insect prey was mimicked by placing the chemical inducers gelatine, salicylic acid and crustacean chitin on leaves. In addition, mechanical stirring of tentacles was performed. Chitinase activity was markedly increased in leaf exudates upon application of notably chitin. Application of gelatine increased the proteolytic activity of leaf exudates, indicating that the reaction of sundew leaves depends on the molecular nature of the inducer applied. In situ hybridization of sundew leaves with a Drosera chitinase probe showed chitinase gene expression in different cell types of non-treated leaves, but not in the secretory cells of the glandular heads. Upon induction, chitinase mRNA was also present in the secretory cells of the sundew leaf. The combined results indicate that chitinase is likely to be involved in the decomposition of insect prey by carnivorous plants. This adds a novel role to the already broad function of chitinases in the plant kingdom and may contribute to our understanding of the molecular mechanisms behind the ecological success of carnivorous plants in nutritionally poor environments.