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Benrey, Betty
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Benrey, Betty
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Betty.Benrey@unine.ch
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- 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 libreThe consequences of squash domestication on the chemical ecology of plant-insect interactions(2021)
; La domestication des plantes ainsi que le début de l’agriculture ont été des innovations clés qui ont modelé la société et l’écosystème que nous connaissons aujourd’hui. La plupart des fruits et légumes que nous consommons ont été sélectionnés par l’homme et divergent des plantes sauvages ancestrales en de nombreux aspects que nous nommons syndrome de domestication. Il s’agit en général d’une augmentation de la taille du fruit, d’un complément en nutriment et, dans 60% des cultures, la réduction de la toxicité dans le but de leur consommation. Cette perte de composé chimique est intimement liée à l’augmentation et la prolifération des ravageurs de cultures. Cependant cette affirmation n’est pas ubiquitaire et dépendant de la plante étudiée. Souvent, la sélection de l’organe d’une plante a lieux en vue de sa consommation alimentaire. D’autres motifs de sélection comme l’utilisation des fibres, fabrication d’huile, décoration comme c’est le cas pour les courges, existent également. Les courges (genre Cucurbita) sont d’origine mexicaine et font partie des premières plantes à avoir été domestiquées sur le continent américain avec le maïs et le haricot. Leur domestication daterait d’il y a 10'000 ans selon des preuves archéologiques. Une de leurs premières utilisations a été en tant que récipient car leur chaire était très amère et toxique à cause d’une molécule nommée cucurbitacine. Il existe cinq espèces différentes de courges, toutes ont été domestiquées principalement pour la consommation de leur fruit, mais également pour leur beauté. La domestication des courges et son impact sur les insectes herbivores n’ayant pas été encore étudié, je me suis lancé le défi de comprendre ses conséquences. J’ai précisément voulu étudier les effets de la domestication sur les défenses physiques (trichomes) et chimiques (cucurbitacines) de la plante de courge et comment ces changements ont impacté les insectes sur plusieurs niveaux trophiques. Pour y répondre, j’ai travaillé sous 4 angles différents : 1) J’ai testé l’hypothèse que le but de domestication de la courge (alimentation ou ornementation) influencerait le contenu en cucurbitacines et trichomes des variétés. Pour cela, j’ai utilisé plusieurs espèces de courges par but de domestication. J’ai étudié l’effet de ces changements de défenses sur deux insectes généralistes se nourrissant soit sur les feuilles (Spodoptera latifascia), soit sur les racines (Diabrotica balteata). J’ai trouvé que les buts de domestication n’expliquaient pas les contenus en cucurbitacines. Cependant, les trichomes ont été diminués sur les variétés sélectionnées pour la consommation de leur fruit. Les cucurbitacines n’ont pas d’impact sur la croissance du stade larvaire des insectes étudiés, en revanche elles attireraient fortement les larves de D. balteata. Cette étude a démontré l’importance de la phylogénie lorsqu’on étudie l’impact de la domestication. 2) J’ai analysé les différences en termes de défense de la plante, entre les courges sauvages et domestiquées de l’espèce Cucurbita argyrosperma. Parmi les courges domestiquées, j’ai gardé le concept de but de domestication en étudiant des variétés sélectionnées pour la consommation du fruit ou l’ornementation. J’ai étudié l’impact de la domestication des courges sur un insecte généraliste (Diabrotica balteata) et un insecte spécialiste des courges (Acalymma vittatum) en laboratoire et dans leur milieu naturel (Mexique). J’ai trouvé que toutes les courges domestiquées ont perdu les cucurbitacines dans leurs racines. Les cotylédons des variétés sélectionnées pour la consommation du fruit contiennent toujours des cucurbitacines mais beaucoup moins que les courges sauvages. Le contenu en cucurbitacine des courges sauvages réduit la croissance des insectes généralistes mais pas des spécialistes. La cucurbitacine est un attractif très fort pour les deux types d’insectes. Au Mexique, les dommages sur les plantes domestiquées étaient plus importants. 3) Je me suis intéressée à l’impact indirect de la domestication des courges sur le troisième niveau trophique (ennemi naturel de l’herbivore). Pour cela j’ai étudié la survie, la préférence et la performance du prédateur Atheta coriaria pour des proies ayant mangé des courges soit sauvages, soit domestiquées. En d’autres termes des larves de Diabrotica balteata qui avaient consommé des racines contenant des cucurbitacines versus des larves qui se sont nourries de racines sans cucurbitacines. J’ai trouvé que la cucurbitacine des plantes sauvages n’a pas impacté la survie ou la préférence du prédateur. La séquestration de cucurbitacine par les herbivores ne les protège en rien contre le prédateur étudié. 4) J’ai voulu comprendre pourquoi les variétés de courge domestiquées ne contiennent pas de cucurbitacine. Plus précisément, j’ai étudié l’impact de la domestication des courges sur l’expression des gènes liés à la biosynthèse de la cucurbitacine. J’ai voulu savoir si les courges domestiquées avaient perdu le gène ou perdu l’expression du gène permettant la production de cucurbitacines. J’ai commencé par trouver des gènes orthologues aux gènes connus chez le concombre. Puis j’ai découvert un candidat pour le gène de la première enzyme responsable de la production de cucurbitacine (cucurbitadienol synthase) et six gènes du cytochrome P-450 responsable d’oxydation permettant la production de cucurbitacines. Ensuite j’ai analysé l’expression de ces gènes dans les racines, cotylédons et feuilles des courges sauvages et domestiquées. J’ai trouvé que les variétés de courge domestiquées possédaient toujours les gènes responsables de la production de cucurbitacine, mais que c’était leur expression qui était perturbée par la domestication. Dans les racines, l’expression des gènes est plus élevée chez les courges sauvages. L’expression de ces gènes est nulle dans les feuilles et très faible dans les cotylédons. ABSTRACT Since the start of agriculture, crop domestication has induced significant changes in both plants and human societies. Plant domestication has generally resulted in decreased chemical and physical defenses in crop plants compared to their wild ancestors. A reduction in plant defensive traits is often expected to result in increased insect performance. By selecting (modifying the genetics) desirable traits for humans, it may favor the pest insects that we have to face today in agriculture. However, recent studies have shown that the impact of crop domestication on plant-insect interactions is not ubiquitous. Surprisingly, there is still much discussion on the way by which crop domestication has influenced insect pests. In my PhD project, I hypothesize that the outcome of plant-insect interactions may be influenced by the type of organ targeted during domestication, as well as the by purpose of domestication. Squash (genus Cucurbita) is one of the earliest and most important domesticated plants in the Americas, along with maize and the common bean. The genus Cucurbita was domesticated on several occasions leading to five different species throughout the Americas, beginning around 10,000 years ago. Wild forms of squash are very bitter and toxic to humans and other mammals because they contain cucurbitacins (toxic secondary metabolites). Squash was domesticated at different times and for different purposes (including soap, oil, music instrument, food and beverage container). As a result, we have great variation on fruits size, color and shape. The aim of my PhD project was to examine the overall consequences of squash domestication on plant defenses and its impact on plant-insect interactions. To date, no studies with these specific questions were done on this important world-wide crop. To meet the challenge, I had four main axes: 1) Study the impact of purpose of domestication on the squash defenses (trichomes and cucurbitacins) and how it altered the interaction with generalist insects (Spodoptera latifascia that eat aboveground tissue and Diabrotica balteata, whose adults feed on aboveground tissues and larvae feed on belowground tissues). To test that, I had squash varieties from different species selected for consumption (fruit and seeds) and varieties selected for an ornamental purpose. I found that the varietal selection rather than the purpose of domestication explained the differences in cucurbitacin content. However, trichome density was reduced on varieties selected for consumption. The herbivore performance was not negatively affected by high cucurbitacin content nor by trichome density. Instead, the root herbivore D. balteata larvae preferred to feed on the varieties with high levels of cucurbitacins. This study highlighted the idea that D. balteata is adapted to cucurbits and the importance of phylogeny while studying plant domestication. 2) Study the consequences of Cucurbita argyrosperma domestication on plant chemical (cucurbitacins) and physical (trichomes) defenses and extent to which altered defenses impacted the interaction with two beetle species, the generalist Diabrotica balteata and the squash specialist, Acalymma spp. (Coleoptera: Chrysomelidae). These plants and insects have a long co-evolutionary history. To add to the behavioral bioassays in the lab, I tested the susceptibility of Cucurbita argyrosperma wild and domesticated varieties in a common garden during a field season in Mexico. I found that cucurbitacins were selected out of the domesticated varieties. Trichome density was not reduced through domestication. Larvae of both insects preferred to feed on roots of wild squash, but this negatively affected the performance of the generalist. In the field, leaves of wild and domesticated plants were mainly attacked by adults of the specialist. 3) Study the indirect consequence of Cucurbita argyrosperma domestication on the third trophic level. One of the main results from previous axes was the reduction of cucurbitacins in domesticated squash varieties. It was hypothesized that D. balteata sequester this compound for its own defense against natural enemies. Then, deprived of cucurbitacin by eating domesticated squash, larvae should be more attractive to soil predators. To test this hypothesis, I used the rove beetle predator (Atheta coriaria), which is a generalist soil predator with no coevolutionary history with D. balteata or squash. Overall, I found no evidence that cucurbitacins serve as a protection against predators. The assumed lethal and deterrent impacts of sequestered cucurbitacin by the herbivore on the predator were not observed. However, the survival of Diabrotica balteata larvae was lower when fed on wild squash populations. 4) Study how squash domestication changed the expression of cucurbitacin biosynthesis genes. From Cucurbita argyrosperma genome and literature on genes involved in the cucurbitacins pathway in cucumber, I targeted seven candidates for cucurbitacins biosynthetic genes. One candidate for the very first enzyme involved in the cucurbitacin biosynthesis: cucurbitadienol synthase, and six cytochrome P-450 enzyme. I analyzed the expression of those genes in roots, cotyledons and leaves to explain the differences in cucurbitacin concentration among plant tissues and among wild and domesticated squash. Overall, gene expression was higher in roots compared to cotyledons and for some genes, wild squash populations had a higher expression than the domesticated varieties. - PublicationMétadonnées seulementPlant species variation in bottom-up effects across three trophic levels: a test of traits and mechanisms(2015-7-21)
; - PublicationAccès libreAssessing the role of native plant growth-promoting Rhizobacteria as bio-inoculants for Yerba Mate ("Ilex paraguariensis")(2015)
; The accelerated process of soil degradation due to long-term inadequate agricultural practices in Misiones, the major productive region of Yerba Mate (Ilex paraguariensis St. Hill.) in Argentina, has led to an urgent need for research and development of more sustainable agricultural practices. Yerba Mate is an emblematic crop in southern South America due to its leaves are used to prepare an energizing beverage called “mate” consumed as an alternative to coffee. The main goal of this study was to evaluate the role of native plant growth promoting rhizobacteria (PGPR) as potential bio-inoculants for Yerba Mate seedlings.
This thesis has shown that biomass yields of Yerba Mate seedlings can be increased up to 183% through bio-inoculation with native PGPR strains. Interestingly, the biomass yield increase was obtained through bio-inoculation in a less fertile soil. Kosakonia radicincitans YD4 was the most effective PGPR strain in enhancing the growth of Yerba Mate seedlings. Bio-inoculation with this strain in soil led to higher yields than those obtained in compost, even though higher yields can be expected in the latter due its high fertility. These results suggested that this strain represents a promising candidate to evaluate its potential as bio-inoculant for this crop in low-productive plantations.
The whole genome of K. radicincitans YD4 was sequenced and annotated to analyze the genetic potential ability to colonize the rhizosphere, and if virulence-associated genes are present in this strain. The presence of genes for chemotaxis, adherence structures (fimbriae) and anti-microbial activities reflected the genetic potential of this strain to colonize and compete successfully in the rhizosphere. Regarding the safety of using YD4 as a bio-inoculant, two gene clusters (Type III and Type VI secretions systems) often associated to pathogenicity were identified. Comparative genomic analysis using closely related pathogenic and PGPR strains suggested that these gene clusters might confer adaptative advantages to YD4 to compete against other microbes and survive in the rhizosphere. This hypothesis has been also proposed for other beneficial plant associated bacteria possessing these gene clusters.
In order to evaluate the ability of the bio-inoculant YD4 to colonize the rhizosphere of Yerba Mate seedlings, a strain-specific real time PCR approach was designed. The dynamics of YD4 was monitored in the rhizosphere of inoculated seedlings during five weeks in nursery. The plant growth-promoting effect of YD4 was confirmed by higher biomass yields and the introduced strain was detected in the rhizospheric soil until the end of the experiment (five weeks). These results suggested that the strain YD4 once inoculated, colonize and remain associated to the rhizosphere exerting its plant growth-promoting effect. Combining these results we can confirm that the isolate YD4 is a PGPR strain with a promising potential to be used as a bio-inoculant for Yerba Mate seedlings.
In the last chapter, the bacterial and fungal root-associated microbiome of Yerba Mate was analyzed for the first time using a pyrosequencing approach. This study aimed at the description of the enriched microbial taxa potentially involved in plant growth promotion inhabiting the roots of this crop. In addition, we analyzed if the agricultural historical management and location sites of Yerba Mate plantations have an effect on the alpha and beta diversity. Our results have shown that the bacterial genera Burkholderia and Enterobacter (containing well-known PGPR representatives) were enriched in Yerba Mate roots, whereas endomycorrhizal fungi were enriched particularly in one low-productive plantation with low soil P content. Yerba Mate trees might be exerting a selective pressure for mycorrhization in this type of plantations. The bacterial community composition, genetic diversity and phylogenetic diversity were significantly influenced by the geographical location of the plantations; whereas the fungal community composition and genetic diversity were significantly affected by the geographical location and soil pH. No effect of the historical agricultural management or location of the plantations was observed on the alpha diversity.
This thesis has contributed with an eco-friendly strategy to improve Yerba Mate growth in nursery, and highlighted the fact that better yields can be obtained thought bio-inoculation in less fertile soils. We are optimistic that this strategy could be exploited in field conditions in the future. - PublicationAccès libreColour polymorphism in the leaf beetle genus 'Oreina'(2013)
; This dissertation investigates the maintenance of colour polymorphism in the leaf beetle genus Oreina CHEVROLAT (Coleoptera; Chrysomelidae). The remarkable colour variation in this seemingly aposematic and chemically defended genus forms a paradox with current scientific views concerning predator learning and mimicry. Using a variety of approaches we explore the selective forces that influence the dynamic colour polymorphic equilibrium. On the basis of a literature review we argue that there isn’t just one selective force of overriding importance but a multitude of factors in a heterogeneous landscape producing a geographic mosaic of coevolution in space and time. Using a phylogenetic approach we analysed the genetic structure and habitat use of Oreina speciosissima populations from the Swiss Alps. Specimens grouped according to their habitat, which was in turn mostly defined by plant associations. Via field experiments we test Müller’s theory of warning colour and mimicry in the wild and prove frequency-dependent selection using tethered beetles exposed to natural predators. By making use of TEM microscopy we prove that colour in Oreina gloriosa is structural and produced by microstructures in the epicuticle. Differences in colour are the result of minute differences in thickness of the electron lucent layers within the chirped multilayer reflector in the beetle’s elytra. I conclude by arguing that there is a multiplicity of factors driving the persisting prevalence of colour polymorphism in Oreina and provide suggestions for further investigation. - PublicationAccès librePopulation genetic structure of two primary parasitoids of Spodoptera frugiperda (Lepidoptera), Chelonus insularis and Campoletis sonorensis (Hymenoptera): to what extent is the host plant important?(2010)
; ; Franck, PierrePlant chemistry can strongly influence interactions between herbivores and their natural enemies, either by providing volatile compounds that serve as foraging cues for parasitoids or predators, or by affecting the quality of herbivores as hosts or prey. Through these effects plants may influence parasitoid population genetic structure. We tested for a possible specialization on specific crop plants in Chelonus insularis and Campoletis sonorensis, two primary parasitoids of the fall armyworm, Spodoptera frugiperda. Throughout Mexico, S. frugiperda larvae were collected from their main host plants, maize and sorghum and parasitoids that emerged from the larvae were used for subsequent comparison by molecular analysis. Genetic variation at eight and 11 microsatellites were respectively assayed for C. insularis and C. sonorensis to examine isolation by distance, host plant and regional effects. Kinship analyses were also performed to assess female migration among host-plants. The analyses showed considerable within population variation and revealed a significant regional effect. No effect of host plant on population structure of either of the two parasitoid species was found. Isolation by distance was observed at the individual level, but not at the population level. Kinship analyses revealed significantly more genetically related—or kin—individuals on the same plant species than on different plant species, suggesting that locally, mothers preferentially stay on the same plant species. Although the standard population genetics parameters showed no effect of plant species on population structure, the kinship analyses revealed that mothers exhibit plant species fidelity, which may speed up divergence if adaptation were to occur. - PublicationMétadonnées seulementThe potential of native parasitoids for the control of Mexican bean beetles: A genetic and ecological approach(2008)
; - PublicationAccès libreEcological distribution and niche segregation of sibling species: the case of bean beetles, Acanthoscelides obtectus Say and A. obvelatus Bridwell(2006)
; 1. Molecular techniques have greatly added to the number of known sympatric cryptic species in insects. Ecological differences between these newly distinguished species are little explored, but niches often appear to overlap strongly. These cases are good models for exploring new ideas about species coexistence and community structure.
2. Acanthoscelides obtectus and A. obvelatus are two sister species of bean bruchids, which have been confused until the last decade. One important ecological difference between them has emerged, however: A. obtectus is multivoltine and now distributed worldwide, whereas A. obvelatus is univoltine and restricted to Mesoamerica. Where their ranges overlap, the two species share the same host plants and larvae can sometimes complete development in the same seed.
3. The analysis of 27 622 Mexican individuals of the two species in 2001-2002 and 2002-2003 indicates that their niches overlap, but are differentiated with respect to altitude and the kind of beans (wild vs. domesticated). The principal patterns in their relative abundance in different habitats, and at different seasons, were constant from one year to the next.
4. As sympatry of these species seems to be of recent origin, the observed niche differentiation may not have evolved in response to competition, but could instead be the consequence of physiological differences, evolved independently in each species in allopatry, that pre-adapted them for different altitudes and kinds of resources.
5. The combination of biological and historical factors thus appears to allow these two sibling species to coexist in sympatry, despite their broadly overlapping ecological niches. - PublicationAccès libreSibling species of bean bruchids: a morphological and phylogenetic study of Acanthoscelides obtectus Say and Acanthoscelides obvelatus Bridwell(2005)
; - PublicationMétadonnées seulementInterpopulation variation in a larval parasitoid of bruchids, Stenocorse bruchivora (Hymenoptera : Braconidae): Host plant effects(2005)
; For parasitoids of herbivores, the two most important biotic factors that will influence their fitness are the host species that they attack and the plant species that the host feeds on. Variation in these two trophic levels because of different habitat characteristics may largely drive the evolution of the interaction between parasitoids and their hosts. Through transplant experiments with three plant-insect populations in Mexico, we examined the consequences of plant variation for the interaction between a bruchid beetle, Zabrotes subfasciatus (Boheman) (Coleoptera: Bruchidae), that feeds on bean seeds of the genus Phaseolus L. (Leguminosae: Phaseolinae) and one of its main parasitoids, Stenocorse bruchivora (Crawford) (Hymenoptera: Braconidae). Results revealed great variation in performance among parasitoid populations. Both the population of origin of the parasitoid and of the host plant influenced the performance of developing parasitoids as well as adult oviposition behavior. Wasps from the Atila population were more likely to parasitize the herbivore and developed faster than wasps from the other two populations, Malinalco and Tepoztlan. The results call be explained in part by the spatial distribution of the host plant, host availability, and seed quality in this population. Variation in performance among parasitoid populations decreased when wasps were exposed to their host in cultivated seeds. This could be caused by the better and less variable quality of this novel resource, and consequently, of the bruchid host. The results from this study indicate that both host plant quality and genetic variation among populations are crucial factors in determining the nature and evolution of the interaction between parasitoids and their herbivorous hosts.
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