Response of a carnivorous plant to simulated herbivory

Studies addressing the impact of herbivory in carnivorous plants are scarce, despite loss of tissue being expected to be costly, as leaves are involved in both energy and nutrient acquisition. We evaluated the effect of simulated herbivory in a population of the carnivorous plant Pinguicula moranensis. We predicted an overall negative impact of herbivory by reducing growth, flowering probability and survivorship. Specifically, we expected that the increase in the negative effect should be related to the amount of leaf area removed. We performed simulated herbivory in plants growing in situ (2015) and ex situ (greenhouse, 2016) using a paper punch (herbivory ranging from 0 to 50%). In the ex-situ experiment, we also tested the effect of availability of resources by implementing a prey addition trial where half of the plants were supplemented with prey (one fruit fly per week). In both experiments, our hypothesis was not supported, as growth, flowering probability and survivorship were not influenced by herbivory treatments. Plants subjected to prey addition did not show higher performance than plants deprived of prey, contradicting our prediction that availability of resources could ameliorate the effect of herbivory. Overall, the lack of differences in performance between undamaged (control) and damaged plants indicate an unexpected short-term ability of P. moranensis to tolerate herbivory, even at high levels of damage.

Prey exclusion combined with simulated fire increases subsequent prey-capture potential in the pale pitcher plant, Sarracenia alata

PREMISE

The association of carnivory (an adaptation to nutrient-poor soils) with fire has been described as a paradox, given increases in nutrient availability that often accompany fire. The nutrients that increase in availability following fire, however, may not be the same as those provided by prey and may not reduce nutrient limitation if accompanied by even greater increases in light.

METHODS

Using a factorial experiment in the field, we examined how simulated fire (clipping plus nitrogen-free fertilizer addition) and prey-derived nutrient availability (prey exclusion) interacted to influence carnivorous potential in Sarracenia alata and belowground competition with its neighbors (manipulated via trenching). We hypothesized that simulated fire combined with prey exclusion would (1) increase the potential for prey capture relative to shade avoidance, hereafter, relative prey-capture potential (RPCP), and/or (2) increase belowground competition with neighboring plants.

RESULTS

Sarracenia alata increased RPCP in response to the combination of simulated fire and prey exclusion, despite increases in phosphorus and other nutrients associated with the simulated fire treatment, suggesting that prey capture potential increases in response to increased nitrogen limitation resulting from increases in light and/or phosphorus after fire. We found no evidence of belowground competition.

CONCLUSIONS

The potential importance of carnivory in Sarracenia alata increases following fire. This result helps to explain the paradoxical association of carnivorous plants with fire by demonstrating the potential for prey-derived nutrient limitation to increase rather than decrease in response to increases in light and nutrients other than nitrogen following fire.

Picky carnivorous plants? Investigating preferences for preys' trophic levels - a stable isotope natural abundance approach with two terrestrial and two aquatic Lentibulariaceae tested in Central Europe

BACKGROUND AND AIMS

Stable isotope two-source linear mixing models are frequently used to calculate the nutrient-uptake efficiency of carnivorous plants from pooled prey. This study aimed to separate prey into three trophic levels as pooled prey limits statements about the contribution of a specific trophic level to the nutrition of carnivorous plants. Phytoplankton were used as an autotrophic reference for aquatic plants as the lack of suitable reference plants impedes calculation of their efficiency.

METHODS

Terrestrial (Pinguicula) and aquatic (Utricularia) carnivorous plants alongside autotrophic reference plants and potential prey from six sites in Germany and Austria were analysed for their stable isotope natural abundances (δ15N, δ13C). A two-source linear mixing model was applied to calculate the nutrient-uptake efficiency of carnivorous plants from pooled prey. Prey preferences were determined using a Bayesian inference isotope mixing model.

KEY RESULTS

Phytophagous prey represented the main contribution to the nutrition of Pinguicula (approx. 55 %), while higher trophic levels contributed a smaller amount (diverse approx. 27 %, zoophagous approx. 17 %). As well as around 48 % nitrogen, a small proportion of carbon (approx. 9 %) from prey was recovered in the tissue of plants. Aquatic Utricularia australis received 29 % and U. minor 21 % nitrogen from zooplankton when applying phytoplankton as the autotrophic reference.

CONCLUSIONS

The separation of prey animals into trophic levels revealed a major nutritional contribution of lower trophic level prey (phytophagous) for temperate Pinguicula species. Naturally, prey of higher trophic levels (diverse, zoophagous) are rarer, resulting in a smaller chance of being captured. Phytoplankton represents an adequate autotrophic reference for aquatic systems to estimate the contribution of zooplankton-derived nitrogen to the tissue of carnivorous plants. The autonomous firing of Utricularia bladders results in the additional capture of phytoplankton, calling for new aquatic references to determine the nutritional importance of phytoplankton for aquatic carnivorous plants.

Regeneration of a keystone semiarid shrub over its range in Spain: habitat degradation overrides the positive effects of plant-animal mutualisms

Global change drivers are currently affecting semiarid ecosystems. Because these ecosystems differ from others in biotic and abiotic filters, cues for plant regeneration and management derived from elsewhere may not be applicable to semiarid ecosystems. We sought to determine the extent to which regional variation in regeneration prospects of a long-lived semiarid keystone shrub depends on anthropogenic habitat degradation, plant-animal interactions and climate determinants. We investigated the regeneration ability (via population size structure, juvenile density and juvenile/adult ratio), fruit set and seed dispersal of Ziziphus lotus in 25 localities spanning the range of its threatened habitats in Spain. We dissected the relative contribution of different regeneration determinants using multiple regression and structural equation modelling. Population regeneration was extremely poor, and size structures were biased towards large classes and low juvenile densities and juvenile/adult ratios. Poor regeneration was often coincident with seed dispersal collapse. However, the positive effect of seed dispersal on population regeneration disappeared after considering its relationship with habitat degradation. Protected areas did have juveniles. Together, these data suggest that habitat degradation directly impacts juvenile establishment. Our results provide insights into habitat and species management at the regional level. Z. lotus populations are currently driven by persistence-based dynamics through the longevity of the species. Nonetheless, collapsed seed dispersal, poor regeneration and the removal of adults from their habitats forecast extinction of Z. lotus in many remnants. The extreme longevity of Z. lotus provides opportunities for recovery of its populations and habitats through effective enforcement of regulations.

Environmental differences between sites control the diet and nutrition of the carnivorous plant Drosera rotundifolia

BACKGROUND AND AIMS

Carnivorous plants are sensitive to small changes in resource availability, but few previous studies have examined how differences in nutrient and prey availability affect investment in and the benefit of carnivory. We studied the impact of site-level differences in resource availability on ecophysiological traits of carnivory for Drosera rotundifolia L.

METHODS

We measured prey availability, investment in carnivory (leaf stickiness), prey capture and diet of plants growing in two bogs with differences in N deposition and plant available N: Cors Fochno (0.62 g m-2 yr.-1, 353 μg l-1), Whixall Moss (1.37 g m-2 yr.-1, 1505 μg l-1). The total N amount per plant and the contributions of prey/root N to the plants' N budget were calculated using a single isotope natural abundance method.

RESULTS

Plants at Whixall Moss invested less in carnivory, were less likely to capture prey, and were less reliant on prey-derived N (25.5% compared with 49.4%). Actual prey capture did not differ between sites. Diet composition differed - Cors Fochno plants captured 62% greater proportions of Diptera.

CONCLUSIONS

Our results show site-level differences in plant diet and nutrition consistent with differences in resource availability. Similarity in actual prey capture may be explained by differences in leaf stickiness and prey abundance.

The Olfactory Neuroecology of Herbivory, Hostplant Selection and Plant-Pollinator Interactions

Plants experience often opposing energetic demands and selective pressures-for instance, where plants need to attract an insect that is both the pollinator and herbivore, or alternately, where plants attract prey (due to limited resources) and pollinators. Together, these selective pressures can modify the volatile signals available to the plant's mutualistic and antagonistic partners. Nevertheless, it remains an open question how changes in the information content of volatile signals modify behavioral responses in mutualists and antagonists, and what the underlying neural bases of these behaviors are. This review focuses on two systems to explore the impact of herbivory and resource availability on plant-pollinator interactions: hawkmoth-pollinated hostplants (where herbivory is common), and carnivorous bee-pollinated pitcher plants (where the plants differentially attract bee pollinators and other insect prey). We focus on (1) the volatile signals emitted from these plants because these volatiles operate as long-distance signals to attract, or deter, insect partners, (2) how this information is processed in the hawkmoth olfactory system, and (3) how volatile information changes spatiotemporally. In both the plants and their respective insect partner(s), volatile signaling, reception and behavior are dynamic and plastic, providing flexibility an ever-changing environment.

The cobra's tongue: Rethinking the function of the "fishtail appendage" on the pitcher plant Darlingtonia californica

PREMISE OF STUDY

Carnivorous pitcher plants employ a variety of putative adaptations for prey attraction and capture. One example is the peculiar forked "fishtail appendage", a foliar structure widely presumed to function as a prey attractant on adult leaves of Darlingtonia californica (Sarraceniaceae). This study tests the prediction that the presence of the appendage facilitates prey capture and can be considered an example of an adaptation to the carnivorous syndrome.

METHODS

In a field experiment following a cohort of Darlingtonia leaves over their growing season, before the pitcher traps opened, the fishtail appendages from half of the leaves were removed. Additionally, all appendages were removed from every plant at two small, isolated populations. After 54 and 104 d, prey items were collected to determine whether differences in prey composition and biomass existed between experimental and unmanipulated control leaves.

KEY RESULTS

Removal of the fishtail appendage did not reduce pitcher leaves' prey biomass nor alter their prey composition at either the level of individual leaves or entire populations. Fishtail appendages on plants growing in shaded habitats contained significantly greater chlorophyll concentrations than those on plants growing in full sun.

CONCLUSIONS

These results call into question the longstanding assumption that the fishtail appendage on Darlingtonia is an adaptation critical for the attraction and capture of prey. I suggest alternative evolutionary explanations for the role of the fishtail structure and repropose a hypothesis on the mutualistic nature of pitcher plant-arthropod trophic interactions.

A novel insight into the cost-benefit model for the evolution of botanical carnivory

BACKGROUND

The cost-benefit model for the evolution of botanical carnivory provides a conceptual framework for interpreting a wide range of comparative and experimental studies on carnivorous plants. This model assumes that the modified leaves called traps represent a significant cost for the plant, and this cost is outweighed by the benefits from increased nutrient uptake from prey, in terms of enhancing the rate of photosynthesis per unit leaf mass or area (AN) in the microsites inhabited by carnivorous plants.

SCOPE

This review summarizes results from the classical interpretation of the cost-benefit model for evolution of botanical carnivory and highlights the costs and benefits of active trapping mechanisms, including water pumping, electrical signalling and accumulation of jasmonates. Novel alternative sequestration strategies (utilization of leaf litter and faeces) in carnivorous plants are also discussed in the context of the cost-benefit model.

CONCLUSIONS

Traps of carnivorous plants have lower AN than leaves, and the leaves have higher AN after feeding. Prey digestion, water pumping and electrical signalling represent a significant carbon cost (as an increased rate of respiration, RD) for carnivorous plants. On the other hand, jasmonate accumulation during the digestive period and reprogramming of gene expression from growth and photosynthesis to prey digestion optimizes enzyme production in comparison with constitutive secretion. This inducibility may have evolved as a cost-saving strategy beneficial for carnivorous plants. The similarities between plant defence mechanisms and botanical carnivory are highlighted.

Effective prey attraction in the rare Drosophyllum lusitanicum, a flypaper-trap carnivorous plant

PREMISE OF THE STUDY

Carnivorous plants have unusually modified leaves to trap insects as an adaptation to low-nutrient environments. Disparate mechanisms have been suggested as luring traits to attract prey insects into their deadly leaves, ranging from very elaborate to none at all. Drosophyllum lusitanicum is a rare carnivorous plant with a common flypaper-trap mechanism. Here we tested whether Drosophyllum plants lure prey insects into their leaves or they act just as passive traps.

METHODS

We compared prey capture between live, potted plants and Drosophyllum-shaped artificial mimics coated with odorless glue. Since this species is insect-pollinated, we also explored the possible existence of a pollinator-prey conflict by quantifying the similarity between the pollination and prey guilds in a natural population. All experiments were done in southern Spain.

KEY RESULTS

The sticky leaves of Drosophyllum captured significantly more prey than mimics, particularly small dipterans. Prey attraction, likely exerted by scent or visual cues, seems to be unrelated to pollinator attraction by flowers, as inferred from the low similarity between pollinator and prey insect faunas found in this species.

CONCLUSIONS

Our results illustrate the effectiveness of this carnivorous species at attracting insects to their flypaper-trap leaves.

Capture of algae promotes growth and propagation in aquatic Utricularia

BACKGROUND AND AIMS

Some carnivorous plants trap not only small animals but also algae and pollen grains. However, it remains unclear if these trapped particles are useless bycatch or whether they provide nutrients for the plant. The present study examines this question in Utricularia, which forms the largest and most widely spread genus of carnivorous plants, and which captures prey by means of sophisticated suction traps.

METHODS

Utricularia plants of three different species (U. australis, U. vulgaris and U. minor) were collected in eight different water bodies including peat bogs, lakes and artificial ponds in three regions of Austria. The prey spectrum of each population was analysed qualitatively and quantitatively, and correlated with data on growth and propagation, C/N ratio and δ(15)N.

KEY RESULTS

More than 50 % of the prey of the Utricularia populations investigated consisted of algae and pollen, and U. vulgaris in particular was found to capture large amounts of gymnosperm pollen. The capture of algae and pollen grains was strongly correlated with most growth parameters, including weight, length, budding and elongation of internodes. The C/N ratio, however, was less well correlated. Other prey, such as moss leaflets, fungal hyphae and mineral particles, were negatively correlated with most growth parameters. δ(15)N was positively correlated with prey capture, but in situations where algae were the main prey objects it was found that the standard formula for calculation of prey-derived N was no longer applicable.

CONCLUSIONS

The mass capture of immotile particles confirms the ecological importance of autonomous firing of the traps. Although the C/N ratio was little influenced by algae, they clearly provide other nutrients, possibly including phosphorus and trace elements. By contrast, mosses, fungi and mineral particles appear to be useless bycatch. Correlations with chemical parameters indicate that Utricularia benefits from nutrient-rich waters by uptake of inorganic nutrients from the water, by the production of more traps per unit of shoot length, and by the capture of more prey particles per trap, as nutrient-rich waters harbour more prey organisms.

Quite a few reasons for calling carnivores 'the most wonderful plants in the world'

BACKGROUND

A plant is considered carnivorous if it receives any noticeable benefit from catching small animals. The morphological and physiological adaptations to carnivorous existence is most complex in plants, thanks to which carnivorous plants have been cited by Darwin as 'the most wonderful plants in the world'. When considering the range of these adaptations, one realizes that the carnivory is a result of a multitude of different features.

SCOPE

This review discusses a selection of relevant articles, culled from a wide array of research topics on plant carnivory, and focuses in particular on physiological processes associated with active trapping and digestion of prey. Carnivory offers the plants special advantages in habitats where nutrient supply is scarce. Counterbalancing costs are the investments in synthesis and the maintenance of trapping organs and hydrolysing enzymes. With the progress in genetic, molecular and microscopic techniques, we are well on the way to a full appreciation of various aspects of plant carnivory.

CONCLUSIONS

Sufficiently complex to be of scientific interest and finite enough to allow conclusive appraisal, carnivorous plants can be viewed as unique models for the examination of rapid organ movements, plant excitability, enzyme secretion, nutrient absorption, food-web relationships, phylogenetic and intergeneric relationships or structural and mineral investment in carnivory.

Genetic structure of the carnivorous plant Pinguicula moranensis (Lentibulariaceae) on the transvolcanic Mexican belt

Most species of Pinguicula present a montane distribution with populations located at high altitudes. In this context, we proposed that populations of Pinguicula species could be genetically differentiated even at a local scale. This study supported that prediction, as a RAPD-based analysis of molecular variance revealed a high degree of genetic structure (Φ (st) = 0.157, P = 0.001) and low gene flow (Nm = 1.0) among four central populations of Pinguicula moranensis in Mexico, with a maximum geographic separation of about 140 km. The four populations also exhibited high levels of genetic diversity (mean Nei's genetic diversity = 0.3716; % polymorphism = 95.45%). The evolutionary implications of the genetic structure found in P. moranensis for other species in the genus are discussed in the context of the naturally fragmented distribution and a set of life history traits shared by most Pinguicula species that could promote geographic isolation and limited gene flow.

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

Carnivory has evolved independently at least six times in five angiosperm orders. In spite of these independent origins, there is a remarkable morphological convergence of carnivorous plant traps and physiological convergence of mechanisms for digesting and assimilating prey. These convergent traits have made carnivorous plants model systems for addressing questions in plant molecular genetics, physiology, and evolutionary ecology. New data show that carnivorous plant genera with morphologically complex traps have higher relative rates of gene substitutions than do those with simple sticky traps. This observation suggests two alternative mechanisms for the evolution and diversification of carnivorous plant lineages. The 'energetics hypothesis' posits rapid morphological evolution resulting from a few changes in regulatory genes responsible for meeting the high energetic demands of active traps. The 'predictable prey capture hypothesis' further posits that complex traps yield more predictable and frequent prey captures. To evaluate these hypotheses, available data on the tempo and mode of carnivorous plant evolution were reviewed; patterns of prey capture by carnivorous plants were analysed; and the energetic costs and benefits of botanical carnivory were re-evaluated. Collectively, the data are more supportive of the energetics hypothesis than the predictable prey capture hypothesis. The energetics hypothesis is consistent with a phenomenological cost-benefit model for the evolution of botanical carnivory, and also accounts for data suggesting that carnivorous plants have leaf construction costs and scaling relationships among leaf traits that are substantially different from those of non-carnivorous plants.

Nutrient limitation and morphological plasticity of the carnivorous pitcher plant Sarracenia purpurea in contrasting wetland environments

* Plasticity of leaf nutrient content and morphology, and macronutrient limitation were examined in the northern pitcher plant, Sarracenia purpurea subsp. purpurea, in relation to soil nutrient availability in an open, neutral pH fen and a shady, acidic ombrotrophic bog, over 2 yr following reciprocal transplantation of S. purpurea between the wetlands. * In both wetlands, plants were limited by nitrogen (N) but not phosphorus (P) (N content < 2% DW(-1), N : P < 14) but photosynthetic quantum yields were high (F(V)/F(M) > 0.79). Despite carnivory, leaf N content correlated with dissolved N availability to plant roots (leaf N vs , r(2) = 0.344, P < 0.0001); carnivorous N acquisition did not apparently overcome N limitation. * Following transplantation, N content and leaf morphological traits changed in new leaves to become more similar to plants in the new environment, reflecting wetland nutrient availability. Changes in leaf morphology were faster when plants were transplanted from fen to bog than from bog to fen, possibly reflecting a more stressful environment in the bog. * Morphological plasticity observed in response to changes in nutrient supply to the roots in natural habitats complements previous observations of morphological changes with experimental nutrient addition to pitchers.

Nutrient limitation and stoichiometry of carnivorous plants

The cost-benefit model for the evolution of carnivorous plants posits a trade-off between photosynthetic costs associated with carnivorous structures and photosynthetic benefits accrued through additional nutrient acquisition. The model predicts that carnivory is expected to evolve if its marginal benefits exceed its marginal costs. Further, the model predicts that when nutrients are scarce but neither light nor water is limiting, carnivorous plants should have an energetic advantage in competition with non-carnivorous plants. Since the publication of the cost-benefit model over 20 years ago, marginal photosynthetic costs of carnivory have been demonstrated but marginal photosynthetic benefits have not. A review of published data and results of ongoing research show that nitrogen, phosphorus, and potassium often (co-)limit growth of carnivorous plants and that photosynthetic nutrient use efficiency is 20 - 50 % of that of non-carnivorous plants. Assessments of stoichiometric relationships among limiting nutrients, scaling of leaf mass with photosynthesis and nutrient content, and photosynthetic nutrient use efficiency all suggest that carnivorous plants are at an energetic disadvantage relative to non-carnivorous plants in similar habitats. Overall, current data support some of the predictions of the cost-benefit model, fail to support others, and still others remain untested and merit future research. Rather than being an optimal solution to an adaptive problem, botanical carnivory may represent a set of limited responses constrained by both phylogenetic history and environmental stress.

The cost of carnivory for Darlingtonia californica (Sarraceniaceae): evidence from relationships among leaf traits

Scaling relationships among photosynthetic rate, foliar nutrient concentration, and leaf mass per unit area (LMA) have been observed for a broad range of plants. Leaf traits of the carnivorous pitcher plant Darlingtonia californica, endemic to southern Oregon and northern California, USA, differ substantially from the predictions of these general scaling relationships; net photosynthetic rates of Darlingtonia are much lower than predicted by general scaling relationships given observed foliar nitrogen (N) and phosphorus (P) concentrations and LMA. At five sites in the center of its range, leaf traits of Darlingtonia were strongly correlated with elevation and differed with soil calcium availability and bedrock type. The mean foliar N : P of 25.2 ± 15.4 of Darlingtonia suggested that these plants were P-limited, although N concentration in the substrate also was extremely low and prey capture was uncommon. Foliar N : P stoichiometry and the observed deviation of Darlingtonia leaf traits from predictions of general scaling relationships permit an initial assessment of the "cost of carnivory" in this species. Carnivory in plants is thought to have evolved in response to N limitation, but for Darlingtonia, carnivory is an evolutionary last resort when both N and P are severely limiting and photosynthesis is greatly reduced.

Resource availability affects investment in carnivory in Drosera rotundifolia

•  Carnivory in plants is restricted to nutrient-poor and open habitats presumably because of high benefits and/or low costs of carnivory in these conditions. Carnivory is costly because the plants need specific adaptations to capture prey. Drosera rotundifolia produces sticky substances on its leaf surface to catch prey. These substances are primarily carbon-based, and their production can be expected to be lower in shade. The benefit of carnivory is in terms of the increased nutritional gain which will be low when inorganic nutrients are available in the growth medium. We expected that investment in carnivory would be lower in shade and nutrient-rich conditions. •  A factorial experiment involving shading and the addition of inorganic nutrients confirmed these predictions in the carnivorous, perennial herb D. rotundifolia. •  Plants growing in shade or in media with nutrients added had less sticky leaves and had reduced their investment in carnivory. •  Interestingly, the observed changes in the stickiness of the leaves were in accord with the carbon/nutrient balance theory, whereas a carbon-based secondary compound, 7-methyljuglone, in the leaves did not respond to shading or nutrient addition.