Voici les éléments 1 - 10 sur 132
  • Publication
    Accès libre
    Odor-based real-time detection and identification of pests and diseases attacking crop plants
    (2024-07-29) ; ;
    Terunobu Akiyama
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    ; ;
    Kosuke Minami
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    ;
    Genki Yoshikawa
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    ;
    Felipe Lopez-Hilfiker
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    ;
    Luca Cappellin
    ;
    Plants respond to attacks by herbivores and pathogens by releasing specific blends of volatile compounds and the resulting odor can be specific for the attacking species. We tested if these odors can be used to monitor the presence of pests and diseases in agriculture. Two methods were used, one employing piezoresistive membrane surface stress sensors and the other proton-transfer reaction mass spectrometry. Under laboratory conditions, both techniques readily distinguished between maize plants that were either undamaged, infested by caterpillars, or infected by a fungal pathogen. Under outdoor conditions, the spectrometer could be used to recognize plants with simulated caterpillar damage with about 80% accuracy. Further finetuning of these techniques should lead to the development of odor-sensing mobile devices capable of alerting farmers to the presence and exact location of pests and diseases in their fields.
  • Publication
    Restriction temporaire
    Influence of biotic and abiotic factors on microbe-induced chemical defences in the "Solanum" clade
    (Neuchâtel : Université de Neuchâtel, 2024) ;
    Plant-associated soil-dwelling microbes, including bacterial and fungi, can greatly facilitate plant mineral nutrition, increase plant tolerance to abiotic stresses such as drought and salinity, as well as induce resistance to biotic stresses like plant pathogens and herbivorous insects. Therefore, using Microbe in agro-ecosystems appears more and more as a promising opportunity to reduce the use of pesticides while improving crop resilience. However, this needs to be further studied. Specifically, the use of microbes to facilitate systemic acquired resistance in plants has been impaired by the observations of strong context dependency. In other word, the effect of microbe-induced resistance (MiR) against pest and pathogens is dependent of plant and microbe genetic make-up, as well as several abiotic components of the environment. Therefore, to better implement microbes in agriculture, we need to better understand induced-defences mechanisms and its dependencies. The PhD project was part of the European research project “Microbe-induced Resistance to Agricultural pests” (MiRA), which aimed to increase knowledge with a view to better use MiR for crop protection. The MiRA project studied MiR mechanisms and impacts on plant performance and biocontrol organisms to improve our ability to predict the effectiveness of MiR according to the growing conditions. In this context, my PhD project aimed at evaluating the environmental dependency of microbe-induced plant resistance. To address this aim, I investigated the effects of abiotic factors as well as the tomato and microbe genotypes on resistance against insect pests and fungal disease. The study focused on the Solanum section Lycopersicon clade, mainly the species Solanum lycopersicum (tomato), and some of its wild ancestors belonging to different biogeographic origins. Concerning resistance-inducing microbes, some strains including arbuscular mycorrhizal fungi (AMF) and plant-growth promoting rhizobacteria (PGPR) were tested. The final aim of the whole project was to improve knowledge for a better efficiency and stability of plant-associated soil microbial products in order to promote a more ecologically-sound crop protection. In the first chapter, I performed a greenhouse experiment for measuring the effect of different AMF inocula (Funneliformis mosseae, Rhizophagus irregularis, or both) on tomato plants (Solanum lycopersicum cv. ‘Moneymaker’) growth and defences against an insect herbivore under two conditions: a normal watering regime or drought conditions. I measured the functional, physiological and chemical traits of the plants. I found that AMF presence generally decreased plant growth, but increased chemical defences and resistance against generalist caterpillars. Such growth‐defence trade‐off was nonetheless dependent on the identity of the mycorrhizal inoculum and on soil water content. Under drought, inoculated tomato plants lowered their investment to defence and uninoculated plants lowered their growth. In the second chapter, I tested the effect of different microbial inocula (AMF and PGPR) on the growth and defence of a domesticated tomato species, the standard commercial cultivar Solanum lycopersicum cv. ‘Moneymaker’, and three wild relative tomato species. I measured functional growth traits and insect herbivory as well as targeted and untargeted chemical traits of the plants. My results showed that domesticated and wild tomato are both affected by the microbial inoculation. I found that PGPR tend to increase, while AMF tend to decrease plant growth, similarly across species. Moreover, using targeted and untargeted metabolomics, I found that soil microbes deeply change the chemistry of the plants, both above- and belowground, in a species-specific manner. In this study, the response of the herbivore insect was more altered by the presence of AMF than the species of tomato. In the third chapter, I experienced the effect of the PGPR Pseudomonas protegens on the growth, chemical defences, and pathogen resistance of a domesticated tomato species, the standard commercial cultivar Solanum lycopersicum cv. ‘Heinz’, hybrids of S. lycopersicum hybrid, and eight wild relatives tomato species. I measured functional growth traits and fungal symptoms as well as targeted and untargeted chemical traits of the plants. My results showed that both the domesticated and wild tomato species can change their phenotype when inoculated with P. protegens. We found that the PGPR tended to enhance fungal resistance, more so for the domesticated species. Moreover, we found clear effects of the PGPR applied on the root on leaf chemistry, but variable across tomato lines. In the fourth chapter, I gathered a review article and a set of original research works done in collaboration with colleagues along the Microbe-induced Resistance to Agricultural pest (MiRA) European project. In the published review article, we proposed an approach that explicitly incorporates context-dependent factors into Induced-systemic resistance research in order to improve the predictability of ISR induction. We also discussed the need to raise awareness for mobilizing interdisciplinary efforts among researchers and stakeholders involved in the development of microbial inoculum. Then, I briefly presented collaborative studies that help to progress in elucidating the role of diverse biotic and abiotic factors in microbe-induced defences. More than to inventory whether beneficial microbes help tomato plants to resist against pests, the project aimed to study how the surrounding environment and the identity of the biotic partners can influence the relationship between the plant and its belowground beneficial organisms, and how this affects its interactions with aboveground threat. My findings show which AMF strains may best perform under stressing drought conditions and that the use of a species-combined inoculum may improve efficiency in variable climatic conditions. All analyses demonstrate that both glycoalkaloid content and broader metabolome of the plant is modified by the either AMF or PGPR inoculum. Another upshot of the thesis is that certain PGPR may have a faster effect on plant growth than AMF and be less costly to plant development but also less efficient on insect pest control. One more outcome of the thesis is to show that domestication of tomato modified plant reaction to beneficial microbes but did not prevent modern cultivars to get profit from the symbiosis relationship. The results of this thesis bring new functional and metabolomic knowledge that can be used to fine-tune the use of beneficial microbes in agriculture and to serve as basis for further research.
  • Publication
    Accès libre
    The relative contribution of the five pedogenesis factors to soil formation and soil organic matter incorporation across environmental gradients
    (Neuchâtel : Université de Neuchâtel, 2024) ; ;
    Le changement climatique devrait remettre en question la persistance future du carbone organique du sol (SOC) dans les écosystèmes terrestres. Compte tenu de la complexité de l'évolution du carbone organique du sol, les interactions plante-sol, les conditions climatiques et les facteurs biotiques sont essentiels pour comprendre le fonctionnement des écosystèmes et la formation des sols. Au cours des dernières décennies, le changement climatique induit par l'homme, la destruction des habitats et les perturbations écologiques ont entraîné des changements significatifs dans la dynamique socio-environnementales, ce qui s'est traduit par une modification des propriétés des sols et de la dynamique des écosytèmes. Ces changements devraient avoir un impact majeur sur les services que les sols rendent à l'homme, menaçant la persistance de nombreuses espèces et, par conséquent, la santé globale des écosystèmes. L'étude des changements du SOC dans un monde en mutation est cruciale pour la compréhension des systèmes environnementaux contemporains. Dans cette thèse, j'ai d'abord cherché à comprendre comment les changements d'environnement entraînent des changements de SOC dans les sols au fil des décennies, en examinant les sols du point de vue d'un gradient environnemental, des rives des lacs aux prairies alpines. Deuxièmement, j'ai étudié comment les conditions environnementales changeantes - en utilisant les gradients d'altitude - conduisent la dynamique de décomposition de la matière organique dans le contexte du changement climatique. La dynamique de décomposition n'est pas seulement influencée par le réchauffement climatique; on s'attend égalmeent à ce qu'elle change en fonction de l'altitude, à mesure que le couvert végétal se modifie et migre vers le haut pour suivre les températures optimales sous l'effet du réchauffement. J'utilise donc l'altitude avec des pentes orientées vers le nord et le sud dans les Alpes suisses pour simuler des scénarios climatiques futurs. L'étude des sols à travers le temps et le gradient environnemental pour prédire le changement de SOC est présentée dans les thèmes 1 et 2. L'étude de la dynamique de décomposition en utilisant les gradients d'altitude pour les variations climatiques ainsi que les pentes orientées nord-sud et les sachets de thé est présentée dans les thèmes 3 et 4. En outre, pour approfondir l'étude de l'effet de la pytochimie des organes végétaux sur la dynamique de décomposition, j'ai utilisé des sacs de litière faits à la main et remplis de matériel végétal local pour montrer comment la phytochimie des feuilles et des racines influence la décomposition de la litère dans le cadre d'une expérience de transplantation de litière (thème 3). Enfin, pour examiner le dernier facteur de formation du sol, mais non le moindre, j'ai également étudié la diversité des microarthropodes le long des gradients d'altitude afin de mieux expliquer les indicateurs écologiques locaux de la biodiversité du sol (thème 4).
  • Publication
    Accès libre
    Solar radiation explains litter degradation along alpine elevation gradients better than other climatic or edaphic parameters
    Organic matter (OM) decomposition has been shown to vary across ecosystems, suggesting that variation in local ecological conditions influences this process. A better understanding of the ecological factors driving OM decomposition rates will allow to better predict the effect of ecosystem changes on the carbon cycle. While temperature and humidity have been put forward as the main drivers of OM decomposition, the concomitant role of other ecosystem properties, such as soil physicochemical properties, and local microbial communities, remains to be investigated within large-scale ecological gradients. To address this gap, we measured the decomposition of a standardized OM source – green tea and rooibos tea – across 24 sites spread within a full factorial design including elevation and exposition, and across two distinct bioclimatic regions in the Swiss Alps. By analyzing OM decomposition via 19 climatic, edaphic or soil microbial activity-related variables, which strongly varied across sites, we identified solar radiation as the primary source of variation of both green and rooibos teabags decomposition rate. This study thus highlights that while most variables, such as temperature or humidity, as well as soil microbial activity, do impact decomposition process, in combination with the measured pedo-climatic niche, solar radiation, very likely by means of indirect effects, best captures variation in OM degradation. For instance, high solar radiation might favor photodegradation, in turn speeding up the decomposition activity of the local microbial communities. Future work should thus disentangle the synergistic effects of the unique local microbial community and solar radiation on OM decomposition across different habitats.
  • Publication
    Accès libre
    Soil properties and plant species can predict population size and potential introduction sites of the endangered orchid Cypripedium calceolus
    Background and Aims To counteract the ongoing worldwide biodiversity loss, conservation actions are required to re-establish populations of threatened species. Two key factors predominantly involved in finding the most suitable habitats for endangered plant species are the surrounding plant community composition and the physicochemical parameters of the soil rooting zone. However, such factors are likely to be context- and species-dependent, so it remains unclear to what extent they influence the performance of target species. Methods We studied large and small Swiss populations of the endangered orchid Cypripedium calceolus. We measured functional traits related to C. calceolus plant and population performance (clonal patch area, plant height, number, of leaf, stems, flowers and fruits), realized vegetation surveys, soil profile analyses, and tested for relationships between plant traits and the surrounding vegetation structure or soil physicochemical parameters. Results Large populations contained bigger patches with more stems and leaves, and produced more flower per individual than small populations. Neither vegetation alliances nor soil classes per se could predict C. calceolus functional traits and population size. However, functional traits explaining population performance and size were related to specific soil parameters (soil organic matter content, pH and phosphorus), in addition to a combination of presence-absence of plant indicator species, relating to ecotones between forests and clearings. Conclusion We show that even for species that can grow across a wide range of vegetation groups both indicator species and specific soil parameters can be used to assess the most favourable sites to implement (re)-introduction actions.
  • Publication
    Accès libre
    Effect of herbivore load on VOC-mediated plant communication in potato
    (2023)
    Carla Vázquez-González
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    Violeta Quiroga
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    Lucía Martín-Cacheda
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    ; ;
    Luis Abdala-Roberts
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    Xoaquín Moreira
    Herbivore-damaged plants emit volatile organic compounds (VOCs) that can alert neighbours and boost their resistance. While VOC-mediated plant communication has been shown to be herbivore-specific, we know little about its contingency on variation in herbivore load. To address this knowledge gap, we tested herbivore load effects on VOC-mediated communication between potato plants (Solanum tuberosum) using the generalist herbivore Spodoptera exigua. First, we tested whether herbivore load (three levels: undamaged control, low, and high load) affected total VOC emissions and composition. Second, we matched emitter and receiver plants and subjected emitters to the same herbivore load treatments. Finally, we performed a bioassay with S. exigua on receivers to test for induced resistance due to VOC-mediated communication. We found that herbivory significantly increased total VOC emissions relative to control plants, and that such increase was greater under high herbivore load. In contrast, we found no detectable effect of herbivory, regardless of the load, on VOC composition. The communication experiment showed that VOCs released by herbivore-induced emitters boosted resistance in receivers (i.e., lower leaf damage than receivers exposed to VOCs released by control emitters), but the magnitude of such effect was similar for both levels of emitter herbivore load. These findings suggest that changes in VOCs due to variation in herbivore load do not modify the outcomes of plant communication.
  • Publication
    Accès libre
    Investigating black rhinoceros ("Diceros bicornis") ecology towards improved conservation and management practices
    Les écosystèmes de savane font face à des pressions croissantes exercées par le changement climatique, la dégradation des écosystèmes et le déclin continu de la biodiversité. En particulier, le déclin des mégafaunes charismatiques en danger telles que les grands herbivores a plusieurs conséquences pour de tels écosystèmes. Celles-ci incluent des impacts tels qu'une stabilité communautaire affaiblie, la modification de la dynamique des chaînes alimentaires et l'altération des cycles des nutriments. Souvent considérés comme des espèces clés, les grands herbivores exercent une influence considérable sur l'ensemble des communautés par le biais de la modification de l'habitat, du partage des ressources et de la compétition. Malgré leur importance écologique et leur statut menacé, les grands herbivores ont été relativement peu étudiés en raison des défis inhérents liés à leur étude, et se trouvent aujourd’hui uniquement dans des zones protégées. Le rhinocéros noir (Diceros bicornis L.) est l'une des espèces de grands herbivores les plus en dangers et a reçu une attention scientifique limitée. La stratégie de rétablissement du rhinocéros noir implique de réintroduire des individus des zones protégées en surplus dans leurs aires historiques, à mesure que les populations atteignent leur capacité de charge. Cela implique de favoriser la croissance des populations dans les aires actuelles et de sélectionner des habitats appropriés pour les translocations. Les défis résident non seulement dans l'identification des facteurs liés à la convenance de l'habitat et au taux de croissance maximisé, mais aussi dans l'intégration des conditions changeantes, telles que les changements dans la composition de la végétation dus au changement climatique et l'influence des herbivores sympatriques. La croissance des populations est étroitement liée non seulement aux conditions abiotiques et biotiques de l'environnement, mais aussi aux actions de gestion. Par conséquent, la recherche sur l'espèce est essentielle pour approfondir nos connaissances écologiques et déterminer si les actions de gestion ont l'effet souhaité en termes d'atteinte des objectifs de conservation. Cette thèse vise à accroître les connaissances univoques de l'écologie du rhinocéros noir, utiles à sa gestion et à celle de son environnement, grâce à une approche contemporaine intégrant des techniques de surveillance et des méthodologies modernes, et trois domaines importants : l'utilisation de l'espace, l'alimentation et les interactions. Ce travail est basé sur plusieurs populations de rhinocéros noirs situées dans des réserves à travers le KwaZulu-Natal, en Afrique du Sud, en particulier celle de Ithala Game Reserve. Dans le Chapitre I, j'étudie l’alimentation et la sélection de l'habitat du rhinocéros noir à travers plusieurs échelles spatiales. En sachant que la sélection de la nourriture est un élément important lié à la distribution spatiale des herbivores, je décris la sélection de la nourriture au moyen de transects d'observation directe sur les sentiers d'alimentation, puis la sélection de l'habitat en fonction des données de monitoring et de la productivité des écosystèmes (NDVI). Je compare la composition nutritionnelle et chimique des espèces végétales préférées et évitées par le biais de la métabolomique (LC-MS) et de l'analyse élémentaire (CHN). Je montre que la distribution spatiale des rhinocéros noirs était négativement associée à la productivité des écosystèmes, mais positivement associée à des types de végétation spécifiques contenant des espèces végétales hautement préférées et chimiquement distinctes. Les rhinocéros noirs occupent donc leur habitat à travers l'espace et le temps en se nourrissant sélectivement de plantes préférées. Dans le Chapitre II, parce que la compréhension des dynamiques interspécifiques des herbivores au sein des zones protégées est cruciale pour leur gestion efficace, le DNA-metabarcoding a été employé pour étudier le partage des ressources entre le rhinocéros noir et trois herbivores sympatriques abondants, l'éléphant, le koudou et l'impala. Bien que des catégories larges de stratégies d'alimentation puissent être utilisées pour expliquer la coexistence, des informations détaillées sur l'alimentation saisonnière sont nécessaires pour évaluer précisément le partage des ressources. Je décris la composition de l'alimentation saisonnière et le chevauchement, et je compare les stratégies d'alimentation entre les quatre herbivores. Je quantifie l'empiétement potentiel sur la niche alimentaire du rhinocéros noir dans Ithala Game Reserve. Je démontre que la composition de l'alimentation et le chevauchement variaient au fil des saisons, la rareté des ressources pendant la saison sèche générant une composition plus uniforme et une réduction du chevauchement des régimes alimentaires. Les mésoherbivores empiétaient davantage sur les rhinocéros noirs que ne le faisaient les éléphants. Dans un environnement plus propice aux brouteurs, les animaux à alimentation mixte, l'éléphant et l'impala, se sont maintenus principalement au broutage tout au long de l'année. Ce chapitre montre que les catégories larges de stratégies d'alimentation et de taille corporelle sont limitées dans leur utilisation dans les zones protégées et que les stratégies saisonnières sont essentielles pour gérer des populations de plus en plus menacées. Dans le Chapitre III, j'étudie les variables potentielles qui influencent la sélection de la nourriture chez le rhinocéros noir. Le comportement alimentaire est régi par des décisions à différentes échelles et façonné par la perception des propriétés morphologiques et physiologiques des plantes. Les signaux pré-ingestifs permettent de différencier et de choisir entre les éléments nutritifs. Ainsi, je compare les caractéristiques et les composés organiques volatils (VOCs, par GC-MS) des espèces végétales préférées et évitées déterminées par des transects de suivi d'alimentation, et j'examine leur importance relative dans la détermination de la préférence ou de l'évitement. Ce chapitre suggère que les signaux à la fois morphologiques et olfactifs sont importants pour la sélection de la nourriture par le rhinocéros noir. Des VOCs discriminants tels que le caryophyllène et l'acétate d'hexénol se sont révélés importants tout au long des saisons, mais les VOCs seuls ne sont pas aussi robustes pour expliquer le choix de la nourriture, notamment pendant la saison de croissance. Ce chapitre marque les premiers pas dans le déchiffrement des facteurs qui influent sur le choix du rhinocéros noir et dans les applications potentielles à la gestion de la conservation. Tenir compte de la capacité à utiliser l'odeur des plantes et des indices morphologiques bénéficieront les modèles liés au comportement alimentaire du rhinocéros noir ainsi qu'aux conséquences pour l'écosystème découlant de ses activités alimentaires. Dans le Chapitre IV, je mesure l'impact du décornage sur les aires de répartition du rhinocéros noir et l'efficacité du décornage en tant que dissuasion contre le braconnage. Etant donné que le braconnage pour les cornes est la plus grande menace pour le rhinocéros noir, en décornant de manière proactive l'ensemble des populations de rhinocéros, les praticiens visent à dissuader le braconnage et à prévenir la perte d'espèces. Cependant, de telles interventions de conservation peuvent avoir des effets cachés et sous-estimés sur le comportement et l'écologie des animaux. Ici, j'utilise des données de surveillance à long terme pour estimer les aires de répartition avant et après le décornage, ainsi que les tendances en matière de décornage et de mortalité. J'estime l'effet d'un tel outil sur les interactions sociales en fonction du chevauchement des aires de répartition. Bien que le décornage préventif dans ces réserves ait coïncidé avec une diminution nationale de la mortalité du rhinocéros noir due au braconnage et n'ait pas entraîné une augmentation de la mortalité naturelle, les rhinocéros noirs décornés ont réduit leur aire de répartition et étaient moins enclins à participer à des interactions sociales. Le décornage des rhinocéros noirs en tant que mesure anti-braconnage modifie leur écologie comportementale, bien que les effets potentiels au niveau de la population de ces changements restent à déterminer. En conclusion, cette thèse suggère que le rhinocéros noir est une espèce complexe qui fait preuve de plasticité comportementale en réponse aux conditions changeantes de l'écosystème et aux interventions de gestion. L'évaluation continue et l'adaptation des stratégies de gestion ainsi qu'une surveillance cohérente sont cruciales pour assurer des efforts de conservation efficaces. L'écologie comportementale, telle que l'utilisation de l'espace et des ressources, peut servir d'indicateurs précoces de conséquences cachées et faciliter la gestion adaptative des grands herbivores. Cette thèse approfondit notre compréhension d'un grand herbivore en danger critique d'extinction et souligne la nécessité de poursuivre la recherche. ABSTRACT Savanna systems are facing growing pressures exerted by climate change, ecosystem degradation and the ongoing decline in biodiversity. Particularly, the decline of endangered charismatic megafauna such as large herbivores, has several consequences for such ecosystems. These include impacts such as weakened community stability, modification of food-web dynamics and alteration of nutrient cycles. Often considered as keystone species, large herbivores, exercise considerable influence on whole communities through habitat modification, resource partitioning, and competition. Despite their significant ecological importance and their threatened status, large herbivores have been relatively under-researched due to the inherent challenges associated with studying them, and are now mostly restricted to protected areas. Black rhinoceros (Diceros bicornis L.) are among the most endangered large herbivore species on Earth and have received limited scientific attention. The strategy for the recovery of black rhino involves restocking historical ranges with surplus animals from protected areas, as populations reach carrying capacity. This implies promoting population growth in current ranges, and selecting suitable habitats for translocations. Challenges lie not only in identifying factors linked to habitat suitability and maximised growth rate but also in integrating changing conditions, such as shifts in vegetation composition due to climate change and the influence of sympatric herbivores. Population growth is intricately connected not only to environmental abiotic and biotic conditions but also to management actions. Hence research on the species is critical in furthering our ecological knowledge and to ascertain whether management actions are having their desired effect in terms of reaching conservation targets. This thesis aims at increasing unambiguous knowledge of black rhino ecology, practical to its management and that of its environment, through a contemporary approach with the integration of monitoring techniques and modern methodologies, and three important scopes: space use, foraging and interactions. This work is based on several black rhino populations situated in reserves across KwaZulu-Natal, South Africa, in particular that of Ithala Game Reserve. In Chapter I, I investigate black rhino forage and habitat selection across multiple spatial scales. Knowing that forage selection is an important component linked to herbivore spatial distribution, I describe forage selection by the means of direct-observation transects on feeding paths and subsequent habitat selection based on monitoring data and ecosystem productivity (NDVI). I compare the nutritional and chemical composition of preferred and avoided plant species through metabolomics (LC-MS) and elemental analysis (CHN). I show that black rhinos’ spatial distribution was negatively associated with ecosystem productivity, but positively associated with specific vegetation types that contain highly preferred, chemically distinct, plant species. Black rhinos thus occupy their habitat across space and time through selective foraging on preferred plants. In Chapter II, because understanding interspecific herbivore dynamics within protected areas is crucial for their effective management, using DNA metabarcoding, I investigate resource partitioning between black rhino and three abundant sympatric herbivores, elephant, kudu and impala. While broad categories of foraging strategies can be used to explain coexistence, fine-grained information on seasonal foraging is needed to precisely assess resource partitioning. I describe seasonal diet composition and overlap; and compare foraging strategies between the four herbivores. I quantify the potential encroachment on black rhino dietary niche in Ithala Game Reserve. I found that diet composition and overlap shifted seasonally, where resource scarcity during the dry season generated a more even composition and reduced overlap of diets. Mesoherbivores encroached more on black rhinos than elephants did. In an environment more suited to browsers, the mixed feeders, elephant and impala, maintained nearly solely browsing through the year. This chapter shows that long-standing broad categories of foraging strategies and body size are limited in their use in protected areas and that seasonal strategies are central to managing increasingly threatened populations. In Chapter III, I investigate potential variables driving black rhino forage selection. Foraging behaviour is governed by decisions at various scales and shaped by the perception of morphological and physiological properties of plants. Pre-ingestive cues allow differentiating and choosing between food items. I thus compare the traits and volatile organic compounds (VOCs, through GC-MS) of preferred and avoided plant species determined by feeding-path transects, and examine their relative importance in determining preference or avoidance. This chapter suggests that both morphological and olfactory cues are important for black rhino forage selection. Discriminant volatiles such as Caryophyllene and Hexenol acetate were found to be important across seasons but volatiles alone were not as robust in explaining choice of forage, particularly in the growing season. This chapter provides the first steps to disentangling factors driving black rhino choice and potential applications to conservation management. Considering the ability to utilise plant odour and morphological cues will aid models pertaining to both the foraging behaviour of black rhino and the ecosystem consequences resulting from their foraging activities. In Chapter IV, I measure the impact of dehorning on black rhino home ranges and the efficacy of dehorning as a poaching deterrent. Because poaching for horns is the biggest threat to black rhino, by proactively dehorning entire rhinoceros populations, conservationists aim to deter poaching and prevent species loss. However, such conservation interventions may have hidden and underestimated effects on animals’ behaviour and ecology. Here, I use long-term monitoring data to estimate home ranges before and after dehorning, and trends in dehorning and mortalities. I estimate the effect of such a tool on social interactions based on home-range overlap. While preventative dehorning at these reserves coincided with a nationwide decrease in black rhino mortality from poaching and did not infer increased natural mortality, dehorned black rhinos decreased their home range area and were less likely to engage in social encounters. Dehorning black rhinos as an anti-poaching measure alters their behavioural ecology, although the potential population-level effects of these changes remain to be determined. In conclusion, this thesis suggests that the black rhino is an intricate species that demonstrates behavioural plasticity to changing ecosystem conditions and management interventions. The ongoing evaluation and adaption of management strategies and consistent monitoring are crucial for ensuring effective conservation efforts. Behavioural ecology, such as space and resource utilisation, can serve as early indicators of concealed consequences and facilitate adaptive management for large herbivores. This thesis furthers our understanding of a critically endangered large herbivore and highlights the need for continued research.
  • Publication
    Accès libre
    Detecting preservation and reintroduction sitesfor endangered plant species using a two-step modelingand field approach
    (2022-8-10) ;
    Broennimann, Olivier
    ;
    Storrer, Yannick
    ;
    ;
    Guisan, Antoine
    ;
    To withstand the surge of species loss worldwide, (re)introduction of endan-gered plant species has become an increasingly common technique in conser-vation biology. Successful (re)introduction plans, however, require identifyingsites that provide the optimal ecological conditions for the target species tothrive. In this study, we propose a two-step approach to identify appropriate(re)introduction sites. The first step involves modeling the niche and distribu-tion of the species with bioclimatic and topographical predictors, both at conti-nental and at national scales. The second step consists of refining thesebioclimatic predictions by analyzing stationary ecological parameters, such assoil conditions, and relating them to population-level fitness values. We dem-onstrate this methodology using Swiss populations of the lady's slipper orchid(Cypripedium calceolusL., Orchidaceae), for which conservation plans haveexisted for years but have generally been unfruitful. Our workflow identifiedsites for future (re)introductions based on the species requirements for mid-to-sunny light conditions and specific soil physico-chemical properties, such asbasic to neutral pH and low soil organic matter content. Our findings showthat by combining wide-scale bioclimatic modeling with fine scale field mea-surements it is possible to carefully identify the ecological requirements of atarget species for successful (re)introductions.
  • Publication
    Accès libre
    Transcriptomic analysis of deceptively pollinated Arum maculatum (Araceae) reveals association between terpene synthase expression in floral trap chamber and species-specific pollinator attraction
    (2022-7-21) ; ;
    Gauthier, Jérémy
    ;
    Gibernau, Marc
    ;
    ;
    Alvarez, Nadir
    Deceptive pollination often involves volatile organic compound emissions that mislead insects into performing nonrewarding pollination. Among deceptively pollinated plants, Arum maculatum is particularly well-known for its potent dung-like volatile organic compound emissions and specialized floral chamber, which traps pollinators—mainly Psychoda phalaenoides and Psychoda grisescens—overnight. However, little is known about the genes underlying the production of many Arum maculatum volatile organic compounds, and their influence on variation in pollinator attraction rates. Therefore, we performed de novo transcriptome sequencing of Arum maculatum appendix and male floret tissue collected during anthesis and postanthesis, from 10 natural populations across Europe. These RNA-seq data were paired with gas chromatography–mass spectrometry analyses of floral scent composition and pollinator data collected from the same inflorescences. Differential expression analyses revealed candidate transcripts in appendix tissue linked to malodourous volatile organic compounds including indole, p-cresol, and 2-heptanone. In addition, we found that terpene synthase expression in male floret tissue during anthesis significantly covaried with sex- and species-specific attraction of Psychoda phalaenoides and Psychoda grisescens. Taken together, our results provide the first insights into molecular mechanisms underlying pollinator attraction patterns in Arum maculatum and highlight floral chamber sesquiterpene (e.g. bicyclogermacrene) synthases as interesting candidate genes for further study.
  • Publication
    Accès libre
    Arbuscular mycorrhizal fungi prevent the negative effect of drought and modulate the growth-defence trade-off in tomato plants
    (2022-6-6) ; ;
    Vergara, Fredd
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    Uthe, Henriette
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    van Dam, Nicole M.
    ;
    Introduction A wide range of arbuscular mycorrhizal fungi (AMF) can be applied to agricultural soils as biofertilizers for increasing crop growth and yield. Current research also shows that AMF can stimulate plant defences against a range of herbivores and pathogens. However, to date, the efficient use of AMF in agriculture is largely impaired by our inability to predict the performance of different AMF-plant complexes in variable environments. For instance, AMFs by increasing plant foraging capacity might alleviate allocation constraints in relation to growth versus defences. However, whether this effect occurs might depend on the in situ conditions. The main goal of this study was to investigate the context-dependency of the ability of AMF to modulate plant growth and resistance against herbivores under variable soil water availability. Materials and Methods To address our goal, we performed a greenhouse experiment for measuring the effect of different AMF inocula (Funneliformis mosseae, Rhizophagus irregularis, or both) on tomato plants (Solanum lycopersicum) growth and defences against an insect herbivore under two conditions: a normal watering regime or drought conditions. We measured the functional, physiological and chemical traits of the plants. Results We found that AMF presence generally decreased plant growth, but increased chemical defences and resistance against generalist caterpillars. Such growth-defence trade-off was nonetheless dependent on the identity of the mycorrhizal inoculum and on soil water content. Under drought, inoculated tomato plants lowered their investment to defence and noninoculated plants lowered their growth. Conclusion This study highlights the influence of abiotic factors and fungal identity on plant–AMF–herbivore interactions. In a broader sense, our results point to the necessity of finding AMF species that have reduced context-dependency to climatic factors, for more widespread use in organic agriculture.