24 research outputs found
Odours in plant-insect interactions beyond communication. Application to the Ficus-pollinator-parasite model and consequences for the understanding of coevolutionary processes
Les odeurs Ă©mises par les plantes sont souvent interprĂ©tĂ©es dans le cadre de leur interaction avec les insectes pollinisateurs, herbivores et ennemis naturels, en tant que signaux de communication dont la fonction est l'attraction ou la rĂ©pulsion de ces insectes. Pourtant, la communication a une dĂ©finition prĂ©cise en biologie Ă©volutive, et le terme « signal » ne doit s'appliquer qu'Ă des traits de l'Ă©metteur qui ont Ă©tĂ© sĂ©lectionnĂ©s dans le cadre de l'interaction avec le rĂ©cepteur par voie sensorielle. De plus, certaines Ă©tudes dĂ©montrent que les ComposĂ©s organiques volatils (COV) Ă©mis par les feuilles participent Ă la dĂ©fense des plantes contre divers stress abiotiques (notamment stress oxydant et thermique) et biotiques (pathogĂšnes, induction des dĂ©fenses). L'idĂ©e de cette thĂšse, c'est d'essayer de faire rentrer l'ensemble de ces contextes et fonctions potentielles dans un cadre commun. En utilisant comme modĂšle les figuiers, leurs pollinisateur et parasites spĂ©cialistes, j'ai choisi comme approche de comparer les variations des odeurs de figue Ă celles de odeurs de feuille, au cours du dĂ©veloppement des figues et au cours d'une journĂ©e. Dans les deux cas, les feuilles constituent un tĂ©moin permettant de dĂ©terminer si les variations observĂ©es peuvent ĂȘtre adaptatives vis-Ă -vis de l'interaction avec les insectes, mais aussi de considĂ©rer explicitement les fonctions potentielles des odeurs Ă©mises en dehors de la rĂ©ceptivitĂ©. Ainsi, les fonctions de protection contre les stress habituellement attribuĂ©es aux odeurs de feuilles sont Ă©galement pertinentes pour les odeurs de figues. A partir de lĂ , le constat que le concept de communication n'est pas pertinent pour dĂ©crire le rĂŽle des odeurs dans les interactions figuier-parasite permet de dĂ©velopper une rĂ©flexion sur la maniĂšre dont les phytophages et leurs ennemis naturels sont susceptibles d'influer sur l'Ă©volution des odeurs Ă©mises par les plantes. Enfin, dans le cas de la communication olfactive figuier-pollinisateur, l'Ă©tude du cas de Ficus septica, chez qui deux pollinisateurs Ă©cologiquement diffĂ©renciĂ©s coexistent, permet d'imaginer un mĂ©canisme potentiel de co-spĂ©ciation Ă©cologique dans lequel la divergence des modalitĂ©s de communication olfactive participerait Ă la mise en place de l'isolement reproducteur.The scents emitted by plants are often interpreted in the light of their interaction with pollinators, phytophagous insects and their natural ennemies, as communication signals whose function is to attract or repel those insects. However, according to the adaptive definition of communication, a trait can be called âsignalâ only if it has been selected for the sensory interaction with a receptor. In addition, it has been shown that the volatile organic compounds (VOC) emitted by leaves participate to the defense of the plant against abiotic (especially oxidative/heat stress) and biotic stresses (pathogens, induction of defenses). The idea underlying this thesis it to put all all the contexts of emission and functions together within a common framework. Using the fig-pollinator-parasite model, the approach I choose was to compare the variation of fig scent with that of leaf scent, along their development and daily. In both cases, leaf scent is a control trait that allows to determine if the variations observed in figs are possibly adaptive regarding the interaction with insects, and to explicitely consider the potential functions of the scents emitted out of receptivity. Stress-protective functions that are evidenced in leaf scents are thus also relevant in figs. Then, the fact that communication is not relevant to describe the role of scents in the fig-parasite interaction led me to develop a reflection on the way phytophagous insects and their natural enemies could influence the evolution of plant scents. Finally, in the case of fig-pollinator communication, studying the case of Ficus septica, that is associated to two co-occuring ecologically differenciated pollinators, allows to imagine a potential co-speciation mechanism, where the divergence of communication mode would contribute to the establishment of reproductive isolation
Host plant species differentiation in a polyphagous oth: olfaction is enough
International audiencePolyphagous herbivorous insects need to discriminate suitable from unsuitable host plants in complex plant communities. While studies on the olfactory system of monophagous herbivores have revealed close adaptations to their host plant's characteristic volatiles, such adaptive fine-tuning is not possible when a large diversity of plants is suitable. Instead, the available literature on polyphagous herbivore preferences suggests a higher level of plasticity, and a bias towards previously experienced plant species. It is therefore necessary to take into account the diversity of plant odors that polyphagous herbivores encounter in the wild in order to unravel the olfactory basis of their host plant choice behaviour. In this study we show that a polyphagous moth, Spodoptera littoralis, has the sensory ability to distinguish five host plant species using olfaction alone, this being a prerequisite to the ability to make a choice. We have used gas chromatography mass spectrometry (GC-MS) and gas chromatography electroantennographic detection (GC-EAD) in order to describe host plant odor profiles as perceived by S. littoralis. We find that each plant emits specific combinations and proportions of GC-EAD active volatiles, leading to statistically distinct profiles. In addition, at least four of these plants show GC-EAD active compound proportions that are conserved across individual plants, a characteristic that enables insects to act upon previous olfactory experiences during host plant choice. By identifying the volatiles involved in olfactory differentiation of alternative host plants by Spodoptera littoralis, we set the groundwork for deeper investigations of how olfactory perceptions translate into behaviour in polyphagous herbivores
Effects of Multi-Component Backgrounds of Volatile Plant Compounds on Moth Pheromone Perception
International audienceThe volatile plant compounds (VPC) alter pheromone perception by insects but mixture effects inside insect olfactory landscapes are poorly understood. We measured the activity of receptor neurons tuned to Z7-12Ac (Z7-ORN), a pheromone component, in the antenna and central neurons in male Agrotis ipsilon while exposed to simple or composite backgrounds of a panel of VPCs representative of the odorant variety encountered by a moth. Maps of activities were built using calcium imaging to visualize which areas in antennal lobes (AL) were affected by VPCs. We compared the VPC activity and their impact as backgrounds at antenna and AL levels, individually or in blends. At periphery, VPCs showed differences in their capacity to elicit Z7-ORN firing response that cannot be explained by differences in stimulus intensities because we adjusted concentrations according to vapor pressures. The AL neuronal network, which reformats the ORN input, did not improve pheromone salience. We postulate that the AL network evolved to increase sensitivity and to encode for fast changes of pheromone at some cost for signal extraction. Comparing blends to single compounds indicated that a blend shows the activity of its most active component. VPC salience seems to be more important than background complexity
Effects of an odor background on moth pheromone communication: constituent identity matters more than blend complexity
Olfaction allows insects to communicate with pheromones even in complex olfactory landscapes. It is generally admitted that, due to the binding selectivity of the receptors, general odorants should weakly interfere with pheromone detection. However, laboratory studies show that volatile plant compounds (VPCs) modulate responses to the pheromone in male moths. We used extracellular electrophysiology and calcium imaging to measure the responses to the pheromone of receptor and central neurons in males Agrotis ipsilon while exposed to simple or composite backgrounds of VPCs. Maps of activities were built using calcium-imaging to visualize which areas in antennal lobes (ALs) were affected by VPCs. To mimic a natural olfactory landscape short pheromone puffs were delivered over VPC backgrounds. We chose a panel of VPCs with different chemical structures and physicochemical properties representative of the odorant variety encountered by a moth. We evaluated the intrinsic activity of each VPC and compared the impact of VPC backgrounds at antenna and antennal lobe levels. Then, we prepared binary, ternary and quaternary combinations to determine whether blend activity could be deduced from that of its components. Our data confirm that a VPC background interfere with the moth pheromone system in a dose-dependent manner. Interference with the neuronal coding of pheromone signal starts at the periphery. VPCs showed differences in their capacity to elicit Phe-ORN firing response that cannot be explained by differences in stimulus intensities because we adjusted the source concentrations to vapor pressures. Thus, these differences must be attributed to the selectivity of ORs or any other olfactory proteins. The neuronal network in the ALs, which reformats the ORN-input, did not improve pheromone salience. We postulate that the AL network might have evolved to increase sensitivity and encode for fast changes over a wide range of concentrations, possibly at some cost for selectivity. Comparing three- or four-component blends to binary blends or single compound indicated that a blend showed the activity of its most active compound. Thus, although the diversity of a background might increase the probability of including a VPC interacting with the pheromone system, chemical diversity does not seem to be a prominent factor per se. Global warming is significantly affecting plant metabolism so that the emissions of VPCs and resulting odorscapes are modified. Increase in atmospheric mixing rates of VPCs will change olfactory landscapes which, as confirmed in our study, might impact pheromone communication
Insect Odorscapes: From Plant Volatiles to Natural Olfactory Scenes
full-text will be published soonInternational audienceOlfaction is an essential sensory modality for insects and their olfactory environment is mostly made up of plant-emitted volatiles. The terrestrial vegetation produces an amazing diversity of volatile compounds, which are then transported, mixed, and degraded in the atmosphere. Each insect species expresses a set of olfactory receptors that bind part of the volatile compounds present in its habitat. Insect odorscapes are thus defined as species-specific olfactory spaces, dependent on the local habitat, and dynamic in time. Manipulations of pest-insect odorscapes are a promising approach to answer the strong demand for pesticide-free plant-protection strategies. Moreover, understanding their olfactory environment becomes a major concern in the context of global change and environmental stresses to insect populations. A considerable amount of information is available on the identity of volatiles mediating biotic interactions that involve insects. However, in the large body of research devoted to understanding how insects use olfaction to locate resources, an integrative vision of the olfactory environment has rarely been reached. This article aims to better apprehend the nature of the insect odorscape and its importance to insect behavioral ecology by reviewing the literature specific to different disciplines from plant ecophysiology to insect neuroethology. First, we discuss the determinants of odorscape composition, from the production of volatiles by plants (section "Plant Metabolism and Volatile Emissions") to their filtering during detection by the olfactory system of insects (section "Insect Olfaction: How Volatile Plant Compounds Are Encoded and Integrated by the Olfactory System"). We then summarize the physical and chemical processes by which volatile chemicals distribute in space (section "Transportation of Volatile Plant Compounds and Spatial Aspects of the Odorscape") and time (section "Temporal Aspects: The Dynamics of the Odorscape") in the atmosphere. The following sections consider the ecological importance of background odors in odorscapes and how insects adapt to their olfactory environment. Habitat provides an odor background and a sensory context that modulate the responses of insects to pheromones and other olfactory signals (section "Ecological Importance of Odorscapes"). In addition, insects do not respond inflexibly to single elements in their odorscape but integrate several components of their environment (section "Plasticity and Adaptation to Complex and Variable Odorscapes"). We finally discuss existing methods of odorscape manipulation for sustainable pest insect control and potential future developments in the context of agroecology (section "Odorscapes in Plant Protection and Agroecology")
Daily Rhythm of Mutualistic Pollinator Activity and Scent Emission in <i>Ficus septica</i>: Ecological Differentiation between Co-Occurring Pollinators and Potential Consequences for Chemical Communication and Facilitation of Host Speciation
<div><p>The mutualistic interaction between <i>Ficus</i> and their pollinating agaonid wasps constitutes an extreme example of plant-insect co-diversification. Most <i>Ficus</i> species are locally associated with a single specific agaonid wasp species. Specificity is ensured by each fig species emitting a distinctive attractive scent. However, cases of widespread coexistence of two agaonid wasp species on the same <i>Ficus</i> species are documented. Here we document the coexistence of two agaonid wasp species in <i>Ficus septica</i>: one yellow-colored and one black-colored. Our results suggest that their coexistence is facilitated by divergent ecological traits. The black species is longer-lived (a few more hours) and is hence active until later in the afternoon. Some traits of the yellow species must compensate for this advantage for their coexistence to be stable. In addition, we show that the composition of the scent emitted by receptive figs changes between sunrise and noon. The two species may therefore be exposed to somewhat different ranges of receptive fig scent composition and may consequently diverge in the way they perceive and/or respond to scents. Whether such situations may lead to host plant speciation is an open question.</p></div
PERMANOVA analysis on the relative composition of scents emitted by <i>Ficus septica</i> and <i>Ficus nota</i> figs and leaves at sunrise and noon.
<p>PERMANOVA analysis on the relative composition of scents emitted by <i>Ficus septica</i> and <i>Ficus nota</i> figs and leaves at sunrise and noon.</p
Flower color polymorphism in Iris lutescens (Iridaceae): Biochemical analyses in light of plantâinsect interactions
International audienceWe describe a flower color polymorphism in Iris lutescens, a species widespread in the Northern part of the Mediterranean basin. We studied the biochemical basis of the difference between purple and yellow flowers, and explored the ecological and evolutionary consequences of such difference, in particular visual discrimination by insects, a potential link with scent emitted and the association between color and scent. Anthocyanins were found to be present in much greater concentrations in purple flowers than in yellow ones, but the anthocyanin composition did not differ between color morphs. Likewise, no quantitative difference in anthocyanin content was found between vegetative tissues of the two morphs. Floral anthocyanins were dominated by delphinidin 3-O-(p-coumaroylrutinoside)-5-O-glucoside (also called delphanin) and its aliphatic derivatives. Small amounts of delphinidin 3-O-(p-caffeoylrutinoside)-5-O-glucoside and its aliphatic derivatives were also characterized. Based on a description of bumblebeesâ (one of the main pollinators of I. lutescens) color perception, purple and yellow flowers of I. lutescens could be visually discriminated as blue and blue-green, respectively, and likely by a wide variety of other insects. The overall chemical composition of the scent produced was not significantly different between morphs, being dominated by terpenoids, mainly myrcene, (E)-ÎČ-ocimene and limonene. A slight color-scent correlation was nevertheless detected, consistent with the shared biosynthetic origin of both pigments and volatile compounds. Therefore in this species, the difference in the amounts of pigments responsible for flower color difference seems to be the major difference between the two morphs. Pollinators are probably the main selective agent driving the evolution of flower color polymorphism in I. lutescens, which represents a suitable species for investigating how such polymorphism is maintained
Daily variation of scent emission rates in <i>Ficus septica</i> and <i>Ficus nota</i>.
<p>Total scent emission rates from (A) figs (”g/fig*hour) and (B) leaves (”g/cm<sup>2</sup>*hour) of both species at sunrise and at noon.</p