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Röder, Gregory
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Röder, Gregory
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gregory.roeder@unine.ch
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Voici les éléments 1 - 10 sur 21
- PublicationAccès libreEffect of herbivore load on VOC-mediated plant communication in potato(2023)
; ; - PublicationAccès libreExperimental Growth Conditions affect Direct and Indirect Defences in two Cotton Species(2023)
; ; ; ; ; ; Cotton has been used as a model plant to study direct and indirect plant defence against herbivorous insects. However, the plant growing conditions could have an important effect on the outcome of such plant defence studies. We examined how common experimental growth conditions influence constitutive and inducible defences in two species of cotton, Gossypium hirsutum and G. herbaceum. We induced plants by applying caterpillar regurgitant to mechanical wounds to compare the induction levels between plants of both species grown in greenhouse or phytotron conditions. For this we measured defence metabolites (gossypol and heliocides) and performance of Spodoptera frugiperda caterpillars on different leaves, the emission of plant volatiles, and their attractiveness to parasitic wasps. Induction increased the levels of defence metabolites, which in turn decreased the performance of S. frugiperda larvae. Constitutive and induced defence levels were the highest in plants grown in the phytotron (compared to greenhouse plants), G. hirsutum and young leaves. Defence induction was more pronounced in plants grown in the phytotron and in young leaves. Also, the differences between growing conditions were more evident for metabolites in the youngest leaves, indicating an interaction with plant ontogeny. The composition of emitted volatiles was different between plants from the two growth conditions, with greenhouse-grown plants showing more variation than phytotron-grown plants. Also, G. hirsutum released higher amounts of volatiles and attracted more parasitic wasps than G. herbaceum. Overall, these results highlight the importance of experimental abiotic factors in plant defence induction and ontogeny of defences. We therefore suggest careful consideration in selecting the appropriate experimental growing conditions for studies on plant defences. - PublicationAccès libreEarly land plants: Plentiful but neglected resources for herbivores ?Il existe entre les organismes vivants de nombreux types d’interactions. Parmi ceux‐ci, figure l’herbivorie qui est la plupart du temps un cas d’antagonisme, au même titre que les relations proieprédateur. Il s’agit d’un phénomène qui est assez bien étudié pour certains groupes de plantes comme les angiospermes (plantes à fleurs), dont le niveau d’évolution est considéré comme le plus élevé, d’où leur nom de « plantes supérieures ». À contrario, d’autres types de plantes sont moins étudiées de manière générale, et en particulier au sujet de l’herbivorie. C’est le cas des mousses, qui sont les premières espèces végétales à avoir colonisé l’habitat terrestre. Celles‐ci ont par conséquent dû développer diverses stratégies lors de leur sortie de l’environnement aquatique, comme une résistance aux rayons UV ainsi qu’à la dessiccation. Les fougères sont également sous‐étudiées alors qu’elles sont quant à elles, les premières à présenter un système vasculaire, nécessaire à une croissance supérieure à une dizaine de centimètres à laquelle sont contraintes les mousses. Les plantes sont constamment soumises à différents stress dans leurs milieux. Ceux‐ci peuvent être abiotiques (i.e. dus à des facteurs environnementaux non vivants tels que la température, l’humidité, la nature du sol, etc.) ou biotiques (i.e. dus à des organismes vivants tels que des pathogènes, des herbivores, d’autres plantes en compétition, etc.). Dans ce travail, une attention particulière est portée sur l’herbivorie. Dans ce cas précis, les végétaux doivent adopter une stratégie pour survivre et plusieurs possibilités s’offrent à eux comme de tolérer les attaques ou de se défendre. L’option de défense se décline en plusieurs facettes, comme de contenir peu de nutriments ou d’arborer des structures physiques comme des épines ou des trichomes. Une autre possibilité est de contenir des molécules chimiques toxiques, pouvant être volatiles ou non. Ces défenses peuvent être combinées et sont également parfois inductibles suite à un stress particulier, phénomène qui est régulé par des phytohormones au sein de la plante. Dans ce travail de thèse, différents types de défenses sont étudiés chez les plantes primitives que sont les mousses et les fougères. Dans un premier chapitre, les recherches se sont focalisées sur le volet nutritif des plantes terrestres primitives. Ainsi, le contenu en nutriments de 15 mousses et fougères a été analysé en termes de protéines, acides aminés et sucres. En parallèle, des feuilles ont été données à manger à deux types d’herbivores : des escargots (Cochlicella baraba) et des chenilles (Spodoptera exigua). Ces deux espèces phytophages généralistes ne se sont pas bien portées ni développées sur les traitements proposés, à l’exception de la diète artificielle et du maïs, utilisés comme contrôles. Cependant, il a été démontré par ce biais que ces végétaux ont des niveaux nutritifs suffisamment élevés pour permettre le développement des organismes phytophages, mais que les compositions en acides aminés et en sucres différents qualitativement. Dans un second chapitre, ce sont les défenses et facteurs physiques qui ont été abordés. Cette fois encore, des bioessais avec des chenilles ont été effectués, mais à l’aide de diète artificielle agrémentée de poudre de plantes primitives. Les insectes utilisés pour cette expérience se sont bien développés sur les diètes contenant du tissu provenant d’une des espèces de mousse, de fougère aquatique ou des plantes à fleurs utilisées comme contrôle. Les performances ont par contre été à nouveau mauvaises sur les espèces de fougères terrestres. Par ailleurs, les éventuelles structures défensives telles que des trichomes ont été investiguées et seule l’espèce de fougère aquatique incluse dans l’étude en présentait à des fins de flottaison. Des analyses du contenu en silice ont été également effectuées et il est assez variable au sein d’une même espèce étudiée et il n’a pas été possible de détecter une différence significative entre les différentes plantes. De plus, aucune corrélation entre le contenu en cet élément n’a pu être établie. La concentration en eau complète les données de cette partie et cette fois, il a été possible de différencier de manière statistiquement significative les espèces de fougères terrestres présentant un contenu en eau inférieur au reste des végétaux employés. Cela suggère cependant que ces défenses physiques ne sont pas impliquées dans la stratégie des plantes inférieures pour lutter contre les herbivores. La suite logique exploitée dans un troisième volet sont les défenses chimiques. Pour cette partie, seules deux espèces de ptéridophytes ont été utilisées, à savoir un lycopode et une fougère. Pour mener à bien les investigations de ce volet, des extractions de composés chimiques ont été réalisées à l’aide de différents solvants tels que de l’eau combinée à 0,1% d’acide formique, du méthanol et du dichlorométhane. Les extraits ainsi obtenus ont été séchés et mélangés à de la diète artificielle afin de nourrir des chenilles polyphages. Celles‐ci ont éprouvé des difficultés à gagner du poids et à se développer sur deux des extraits effectués sur la fougère. Celui réalisé avec un solvant aqueux a été fractionné et ces parties à nouveau ajoutées à de la diète artificielle pour être également proposée à des larves de mites. L’une des fractions s’est avérée plus toxique que les autres et contenait des phloroglucinols, une classe de molécules connue pour être impliquée dans la défense de plantes comme l’eucalyptus. Il a donc été conclu que ces molécules jouent probablement le même rôle pour l’espèce de fougère étudiée ici. Dans un quatrième chapitre de ce travail, ce sont les phytohormones et les composés organiques volatils (COVs) émis par une espèce de fougère qui ont été investigués. Ces composés ont été mesurés après l’attaque de pucerons spécialisés (Idiopterus nephrelepidis) ou de chenilles (S. exigua), ou encore suit à des dégâts mécaniques. Il n’a pas été possible de détecter une réponse hormonale des plantes, ni de détecter de changement au niveau des COVs émis suite à l’agression par les insectes piqueurssuceurs. En revanche, il a été démontré que cette espèce de fougère change d’odeur lorsqu’elle est consommée par la chenille ou soumise à des blessures seules, ces deux cas étant discernables entre eux. Ce mécanisme n’est donc pas limité aux plantes à fleurs et pourrait être utile aux ptéridophytes pour, par exemple, attirer des auxiliaires comme des parasitoïdes, les aidant à lutter contre les assaillants. Dans l’ensemble, les résultats de ce travail de doctorat démontrent que la problématique de l’herbivorie chez les plantes inférieure est complexe et mérite l’attention de la recherche, tout en soulignant l’importance de l’étude de ces groupes de plantes dans une perspective évolutionnaire. De plus, ces plantes sont dites primitives, mais nous observons les représentants actuels qui font face aux mêmes contraintes que les plantes dites supérieures et ont dû s’adapter tout autant qu’elles à leur environnement. ABSTRACT There are many types of interactions between living organisms. Among these, we can find the herbivory interaction. This is most of the time a case of antagonism, as are prey‐predator relationships. This is a phenomenon that is fairly well studied for certain groups of plants such as angiosperms (flowering plants). These plants are considered to be at the highest level of evolution and are referred as "higher plants". On the other hand, other types of plants are less studied in general, and in particular on the subject of herbivory. This is the case for the bryophytes, which are the first plant species to have colonized the terrestrial habitat. They had to develop various strategies during their ground colonization, such as resistance to UV radiation and desiccation. Ferns are also under‐studied, but they are the first group in evolution presenting a vascular system, necessary for a growth superior to about ten centimeters to which mosses are constrained. Plants are constantly subjected to different stresses in their environments. These can be abiotic (i.e. due to non‐living environmental factors such as temperature, humidity, soil type, etc.) or biotic (i.e. due to living organisms such as pathogens, herbivores, other plants in competition, etc.). In this work, a particular focus is made on herbivory. In this interaction, plants must adopt a strategy to survive to herbivores’ consumption and several possibilities are offered to them. Indeed, they can tolerate the attacks or defend themselves. This last option is declined in several facets, like having a low nutrients content or like exhibit physical structures as spines or trichomes. Another possibility is to contain toxic chemical compounds, which can be volatile or not. These defenses can be combined and are also sometimes inducible by a particular stress. This phenomenon is regulated by phytohormones in the plant. In this thesis, different types of defenses are studied in primitive plants such as mosses and ferns. Thus, in a first chapter, the nutrient content of 15 mosses and ferns was analyzed in terms of proteins, amino acids and sugars. In parallel, leaves were fed to two types of herbivores: snails (Cochlicella baraba) and caterpillars (Spodoptera exigua). These two generalist phytophagous species do not survive nor develop sustainably to their reproductive adult stage on the proposed treatments, except for the artificial diet and maize, used as controls. However, it was shown that these plants have a high enough nutrient level to allow development, but that the compositions in amino acids and sugars differ qualitatively. In a second chapter, defenses and physical factors were addressed. Bioassays with caterpillars were also carried out in this part. The treatment proposed to the herbivores were artificial diet mixed with powder made from 15 different primitive plants and two flower plants or no plant used as control. We obtained results showing that the insects grew well on diets containing tissue from one of the bryophyte species, from the aquatic fern, or from one of the flowering plants used as a control. In addition, possible structures such as trichomes were investigated. The aquatic fern species included in the study was the only species that shown these structures, but uses them for flotation purposes, rather than as defensive weapon. Water and silica content analyses complete the data collected in this chapter. Silica concentration is quite variable, intra‐ and interspecifically speaking. It was not possible to detect a significant difference between different plants. Moreover, no correlation between the content of this element could be established. On the other hand, it was possible to differentiate in a statistically significant way the species of ground ferns with a lower water content than the rest of the plants used. This suggests, however, that these physical defenses are not involved in the lower plants' strategy to combat herbivores. The next chapter was dedicated to the chemical defenses. For this part, only two species of pteridophytes were used, namely a lycopod and a fern. To carry out the investigations of chemical defenses, extractions were carried out using different solvents, such as water combined with 0.1% formic acid, methanol, and dichloromethane. The extracts obtained were dried and mixed with artificial diet. Those supplemented diets were then used to feed polyphagous caterpillars. These insects had difficulty gaining weight and developing on two of the extracts made with the fern species. In a second step, fractions were made from the worst extract, the aqueous one. The fractions were again added to artificial diet and offered to the caterpillars. One of the fractions was found to be more toxic than the others, and contained phloroglucinols. This is a class of compounds known to be involved in the defense of plants like eucalyptus. It was therefore concluded that these molecules might play the same role for the fern species studied here. In the fourth chapter of this thesis, phytohormones and volatile organic compounds (VOCs) emitted by a fern species after attacks by specialized aphids (Idiopterus nephrelepidis) or caterpillars (S. exigua), or mechanical damage were investigated. It was not possible to detect a hormonal response of the plants. Change in the VOCs emitted as a result of the aggression by the aphids were, as well, not detectable. On the other hand, it was shown that this fern species changes its odor when consumed by caterpillars or when subjected to wounds alone, both cases being discernible. This mechanism is therefore not limited to flowering plants and could be useful for pteridophytes. We can hypothesize that they would attract beneficials such as parasitoids, helping them to overcome herbivores’ attacks. Overall, the results of this PhD demonstrate that the study of herbivory in lower plants is complex and deserves research attention, while highlighting the importance of studying these plant groups from an evolutionary perspective. Moreover, these plants are called “primitive”, but their present‐day representatives encounter the same constraints as the so‐called higher plants. The early land plants are as successful and adapted to their environment as the flowering plants.
- PublicationAccès libreBioturbation by endogeic earthworms facilitates entomopathogenic nematode movement toward herbivore‑damaged maize roots(2020-12-4)
; ; ; ; Entomopathogenic nematodes (EPNs) have been extensively studied as potential biological control agents against root-feeding crop pests. Maize roots under rootworm attack have been shown to release volatile organic compounds, such as (E)-β-caryophyllene (Eβc) that guide EPNs toward the damaging larvae. As yet, it is unknown how belowground ecosystems engineers, such as earthworms, affect the biological control capacity of EPNs by altering the root Eβc-mediated tritrophic interactions. We here asked whether and how, the presence of endogeic earthworms affects the ability of EPNs to find root-feeding larvae of the beetle Diabrotica balteata. First, we performed a field mesocosm experiment with two diverse cropping systems, and revealed that the presence of earthworms increased the EPN infection potential of larvae near maize roots. Subsequently, using climatecontrolled, olfactometer-based bioassays, we confirmed that EPNs response to Eβc alone (released from dispensers) was two-fold higher in earthworm-worked soil than in earthworm-free soil. Together our results indicate that endogeic earthworms, through burrowing and casting activities, not only change soil properties in a way that improves soil fertility but may also enhance the biocontrol potential of EPNs against root feeding pests. For an ecologically-sound pest reduction in crop fields, we advocate agricultural practices that favour earthworm community structure and diversity. - PublicationAccès libreElevational gradients in constitutive and induced oak defences based on individual traits and their correlated expression patterns(2020-12-2)
; ; - PublicationAccès libreThe smell of hunger: Norway rats provision social partners based on odour cues of need(2020-3-24)
; Taborsky, MichaelWhen individuals exchange helpful acts reciprocally, increasing the benefit of the receiver can enhance its propensity to return a favour, as pay-offs are typically correlated in iterated interactions. Therefore, reciprocally cooperating animals should consider the relative benefit for the receiver when deciding to help a conspecific. Norway rats (Rattus norvegicus) exchange food reciprocally and thereby take into account both the cost of helping and the potential benefit to the receiver. By using a variant of the sequential iterated prisoner’s dilemma paradigm, we show that rats may determine the need of another individual by olfactory cues alone. In an experimental food-exchange task, test subjects were provided with odour cues from hungry or satiated conspecifics located in a different room. Our results show that wild-type Norway rats provide help to a stooge quicker when they receive odour cues from a hungry rather than from a satiated conspecific. Using chemical analysis by gas chromatography-mass spectrometry (GC-MS), we identify seven volatile organic compounds that differ in their abundance between hungry and satiated rats. Combined, this “smell of hunger” can apparently serve as a reliable cue of need in reciprocal cooperation, which supports the hypothesis of honest signalling. - PublicationRestriction temporaireThe combined use of an attractive and repellent sex pheromonal component by a gregarious parasitoid(2019-3-28)
; ; ; ; ; Gregarious parasitoids usually clump their cocoons together and the adults emerge in a synchronized fashion. This makes it easy for them to find mating partners and most copulations indeed take place at the natal patch. Yet, males should leave such sites when females are no longer receptive. As yet, this decision-making process and the possible involvement of pheromones were poorly understood. Here we report on a remarkable use of attractive and repellent pheromones of the well-studied gregarious parasitoid species Cotesia glomerata (L.) (Hymenoptera: Braconidae). Virgin C. glomerata females were found to release an attractive as well as a repellent compound, which in combination arrest males on the natal patch, but after mating the females stop the production of the attractant and the males are repelled. The repellent compound was identified as heptanal, which was also released by males, probably reducing male-male competition on the natal patch. We also confirmed that the sex ratio of the emerging wasps can vary considerably among patches, depending on the relative quality of hosts and the number of females that parasitize a host. The newly revealed use of attractive and repellent pheromone compounds by C. glomerata possibly helps maximize mating success under these variable conditions. - PublicationRestriction temporaireEnvironmental gradients and the evolution of tri‐trophic interactions(2018-11-28)
; ; Long‐standing theory predicts herbivores and predators should drive selection for increased plant defences, such as the specific production of volatile organic compounds for attracting predators near the site of damage. Along elevation gradients, a general pattern is that herbivores and predators are abundant at low elevation and progressively diminish at higher elevations. To determine whether plant adaptation along such a gradient influences top‐down control of herbivores, we manipulated soil predatory nematodes, root herbivore pressure and plant ecotypes in a reciprocal transplant experiment. Plant survival was significantly higher for low‐elevation plants, but only when in the presence of predatory nematodes. Using olfactometer bioassays, we showed correlated differential nematode attraction and plant ecotype‐specific variation in volatile production. This study not only provides an assessment of how elevation gradients modulate the strength of trophic cascades, but also demonstrates how habitat specialisation drives variation in the expression of indirect plant defences. - PublicationRestriction temporaireRoot-colonizing bacteria enhance the levels of (E)-β-caryophyllene produced by maize roots in response to rootworm feeding(2018-2-9)
; ; - PublicationAccès libreFormal comment to Soler et al.: Great spotted cuckoo nestlings have no antipredatory effect on magpie or carrion crow host nests in southern Spain(2017-9-18)
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