139 research outputs found
Genetic variation and trait plasticity in plant defence suppression
No full textAs plantas evoluíram um conjunto complexo de defesas, algumas delas induzíveis por herbivoria. Por sua vez, os herbívoros evoluíram para lidar com tais defesas, sendo que alguns conseguem suprimir as defesas do hospedeiro, geralmente através de efetores salivares. Apesar de crucial para a otimização do controlo de pragas, a variação genética e plasticidade da supressão de defesas é ainda pouco estudada. Assim sendo, esta tese teve como objetivo ampliar o conhecimento sobre a variabilidade genética e o impacto do ambiente na supressão de defesas. Para isso, estudei as pragas de tomateiros Tetranychus urticae e T. evansi, nas quais algumas populações conseguem suprimir defesas. Primeiro, estudei se a supressão de defesas é variável e como é que se correlaciona com a fecundidade de T. evansi. Observei que, apesar da supressão ser variável, a fecundidade não está correlacionada com os seus diferentes níveis. De seguida, avaliei se a supressão é comum em populações naturais de T. urticae obtidas de tomateiros. Descobri que esse era o caso, e que o gene effector 84 é altamente variável nesta espécie. De seguida, demonstrei que a supressão é mantida a uma temperatura elevada, apesar da expressão do effector 84 diminuir, sugerindo plasticidade. Para além disso, modelos de dinâmica populacional revelaram que uma temperatura elevada favorece ácaros T. urticae que suprimem defesas, excluindo ácaros que induzem defesas. Finalmente, observei que plantas infestadas com supressores não conseguem estabelecer defesas contra uma densidade alta de herbívoros, ao contrário de quando infestadas com indutores. Os meus resultados mostram que ambas as espécies têm variabilidade genética para a supressão de defesas e que a expressão do effector 84 é plástica com a temperatura. Esta tese oferece informações relevantes sobre como a supressão de defesas pode evoluir e ser mantida na natureza, uma vez que sugere que a adaptação ao hospedeiro e alterações na temperatura podem ser fatores importantes para a sua seleção, com implicações na gestão de pragas.Whereas many herbivores induce plant defences, many others can suppress them. Defence suppression promotes herbivore performance, and it is mediated via herbivore-derived compounds called effectors, often peptides produced in the salivary glands of herbivores. be Although crucial for optimizing pest control, the genetic variation and plasticity of defence suppression in herbivore communities is poorly understood. As such, this thesis aimed to increase knowledge on these. In this thesis, I studied the destructive pests Tetranychus urticae and T. evansi species, in which some populations can suppress tomato plant defences. First, I investigated if traits related to defence suppression in T. evansi are genetically variable and how this variation correlates with mite fecundity. I found that fecundity is a genetic variable for T. evansi but it is not affected by varying degrees of tomato JA defences. Then, we evaluated if defence suppression is a common trait among field T. urticae mites collected from tomato plants. I found this to be true and that the salivary effector 84 is highly variable in this species. Next, I showed that defence suppression is maintained at a high temperature, although the expression of effector 84 decreases, suggesting plasticity. Also, population dynamics models revealed that a high temperature may favour T. urticae mites that suppress defences, possibly displacing T. urticae inducer mites. Finally, I revealed plants infested with suppressor mites are compromised in mounting defences in a density-dependent manner, as opposed to inducer mites. My findings show that both mite species have genetic variation for defence suppression and that effector expression is plastic with temperature. This thesis also offers powerful insights into how defence suppression can evolve and be maintained in nature, as it suggests that host adaptation and high temperatures could be drivers for the selection of such a trait, with implications for crop pests management.Dutch Research Council através dos projetos ALWOP.283, NWO-VICI 1939
Genetic variation and trait plasticity in plant defence suppression
No full textAs plantas evoluíram um conjunto complexo de defesas, algumas delas induzíveis por herbivoria. Por sua vez, os herbívoros evoluíram para lidar com tais defesas, sendo que alguns conseguem suprimir as defesas do hospedeiro, geralmente através de efetores salivares. Apesar de crucial para a otimização do controlo de pragas, a variação genética e plasticidade da supressão de defesas é ainda pouco estudada. Assim sendo, esta tese teve como objetivo ampliar o conhecimento sobre a variabilidade genética e o impacto do ambiente na supressão de defesas. Para isso, estudei as pragas de tomateiros Tetranychus urticae e T. evansi, nas quais algumas populações conseguem suprimir defesas. Primeiro, estudei se a supressão de defesas é variável e como é que se correlaciona com a fecundidade de T. evansi. Observei que, apesar da supressão ser variável, a fecundidade não está correlacionada com os seus diferentes níveis. De seguida, avaliei se a supressão é comum em populações naturais de T. urticae obtidas de tomateiros. Descobri que esse era o caso, e que o gene effector 84 é altamente variável nesta espécie. De seguida, demonstrei que a supressão é mantida a uma temperatura elevada, apesar da expressão do effector 84 diminuir, sugerindo plasticidade. Para além disso, modelos de dinâmica populacional revelaram que uma temperatura elevada favorece ácaros T. urticae que suprimem defesas, excluindo ácaros que induzem defesas. Finalmente, observei que plantas infestadas com supressores não conseguem estabelecer defesas contra uma densidade alta de herbívoros, ao contrário de quando infestadas com indutores. Os meus resultados mostram que ambas as espécies têm variabilidade genética para a supressão de defesas e que a expressão do effector 84 é plástica com a temperatura. Esta tese oferece informações relevantes sobre como a supressão de defesas pode evoluir e ser mantida na natureza, uma vez que sugere que a adaptação ao hospedeiro e alterações na temperatura podem ser fatores importantes para a sua seleção, com implicações na gestão de pragas.Whereas many herbivores induce plant defences, many others can suppress them. Defence suppression promotes herbivore performance, and it is mediated via herbivore-derived compounds called effectors, often peptides produced in the salivary glands of herbivores. be Although crucial for optimizing pest control, the genetic variation and plasticity of defence suppression in herbivore communities is poorly understood. As such, this thesis aimed to increase knowledge on these. In this thesis, I studied the destructive pests Tetranychus urticae and T. evansi species, in which some populations can suppress tomato plant defences. First, I investigated if traits related to defence suppression in T. evansi are genetically variable and how this variation correlates with mite fecundity. I found that fecundity is a genetic variable for T. evansi but it is not affected by varying degrees of tomato JA defences. Then, we evaluated if defence suppression is a common trait among field T. urticae mites collected from tomato plants. I found this to be true and that the salivary effector 84 is highly variable in this species. Next, I showed that defence suppression is maintained at a high temperature, although the expression of effector 84 decreases, suggesting plasticity. Also, population dynamics models revealed that a high temperature may favour T. urticae mites that suppress defences, possibly displacing T. urticae inducer mites. Finally, I revealed plants infested with suppressor mites are compromised in mounting defences in a density-dependent manner, as opposed to inducer mites. My findings show that both mite species have genetic variation for defence suppression and that effector expression is plastic with temperature. This thesis also offers powerful insights into how defence suppression can evolve and be maintained in nature, as it suggests that host adaptation and high temperatures could be drivers for the selection of such a trait, with implications for crop pests management.Dutch Research Council através dos projetos ALWOP.283, NWO-VICI 1939
Consequences of russet mite-induced tomato defenses for community interactions
No full textPlants make use of inducible defenses to resist herbivores. Two hormone signaling pathways play a major role in the regulation of these defense responses: the JA pathway and the SA pathway, and these two are well-known to antagonize each other’s action. Some herbivores evolved traits to interfere with induced defenses but the extent to which such traits promote the success of competitors as well is unclear. The research described in this thesis shows that defense suppression is favourable for herbivores but can backfire within natural communities. I found that russet mites (Aculops lycopersici), a major pest of tomato, facilitate their natural spider mite competitors and suppress jasmonate (JA) defenses, which would otherwise hinder their growth. Although russet mites also induce salicylate (SA), suppression of JA-defenses appeared SA-independent. However, induction of SA did account for the facilitation of spider mites, thereby inhibiting the russet mite’s population growth. This means that whether or not host-defense manipulation improves a herbivore’s fitness depends on interactions with other attackers via induced-host defenses. Predatory mites (A. limonicus) were able to establish themselves on russet mite-infested plants because of the degradation of trichomes that is associated with russet mite herbivory, However, biological control was still insufficient, likely due to the fact that too many russet mites still receive protection from predation from trichomes that have not yet degraded. Sequencing of the russet mite genome allowed for the discovery of candidate effector proteins, which might be involved in russet mite-induced defense suppression as well as trichome degradation
Defense suppression benefits herbivores that have a monopoly on their feeding site but can backfire within natural communities
No full text<p>Raw data including popution densities, mite fecundity, plant gene expression, phytohormone and bacterial growth data. November 2014.</p
Temporal and stage-specific variation in mite-induced responses of tomato plants
No full textPlants have evolved a rich array of defenses to resist being eaten by herbivores. Spider mites - a group of herbivorous mites - generally induce a combination of JA- and SA- regulated defenses. Solanaceae specialist Tetranychus evansi and some strains of the generalist two-spotted spider mite, Tetranychus urticae were observed to suppress these defenses. This suppression was found to benefit attacking spider mites. In this thesis, I have investigated the robustness of the plant defense induction and suppression framework by introducing more system complexity (mainly variation in abiotic conditions same as in greenhouses and in nature) into the experiments. First, herbivore life stage was found to be a relevant factor when investigating plant responses to spider mites especially for determining which type of defense (i.e., JA or SA) is most relevant for plant resistance. Subsequently, induced SA- and JA-related defenses are subject to diurnal variation possibly causing tomatoes to incur more feeding damage during the dark phase. Mites, especially T. evansi, relax effector production during the dark phase. Further investigation of the effects of a small group of putative secreted effector proteins on plants did not find (direct) evidence that these mite proteins decrease plant palatability via an effect on defenses. The yeast-two-hybrid screens revealed predominantly plant target-proteins associated with different aspects of SA-mediated defenses, the effect of SHOT proteins on defenses may be post-translational. Finally, it was shown that plants have plastic control over reproduction and can speed up fruit and seed production when conditions are unfavorable
Molecular sabotage of host plant defenses by spider mites
No full textPlants constitute an ample source of nutrients for a diversity of organisms that include viruses, microbes, nematodes, insects, and mites. To protect their resources, plants possess a robust immune system that establishes structural and biochemical defenses to fight invaders. Some of these defenses are highly effective but often are very costly to sustain. Thus plants have developed inducible defenses, i.e. they are only produced when needed, regulated by a highly interconnected network in which hormones and protein hubs play important roles. However, plant diseases and pest outbreaks still occur. Many successful plant parasites manipulate the regulation of their host inducible defenses, and often they do so by employing specialized secreted proteins that sabotage the plant immunity network. In phytopathology these proteins are known as effectors. In this thesis I have discovered an arsenal of effector proteins in spider mites, particularly in the saliva of two spotted spider mite (Tetranychus urticae) and the red tomato spider mite (T. evansi), both of which are problematic pests in agriculture. These small herbivores are able to suppress plant defenses, particularly those regulated by the phytohormones jasmonic acid (JA) and salicylic acid (SA), and in this thesis I postulate that spider mites likely achieve such feats by using their effector arsenal
Plant Responses to Phytophagous Mites/Thrips and Search for Resistance
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Monopile installation assessment: A critical assessment of an oscillating monopile during offshore installation
No full textAn offshore wind turbine requires a stable support structure to support the tower and nacelle. The support structure in the form of a monopile is lowered to the seabed and hammered in the soil. During the lowering process the monopile may show excessive motions, that occur on an irregular basis. The cause for this is unknown. This thesis is devoted to find the cause, to prevent this from happening in future operations. First off a literature study and analysis of the environmental conditions is carried out. A study in the mechanical behaviour of the system will provide a good perspective on the situation. Finally, the cause is verified with model tests and a numerical model is validated. From the environmental conditions wind and current are expelled as (main) contributor. Data analysis and system analysis conclude that waves are the main cause for the problem. In the model tests this cause is validated together with the mechanical behaviour (natural frequency) of the system. The natural frequency of the monopile is depending on the waterlevel. Wave frequencies (in the spectrum) close to the natural frequency cause a resonance phenomenon, with large monopile motions as consequence. A numerical model, based on a mechanical system and the Morison's equation is validated. The numerical model is a good and fast solution for modeling monopile motions, from wave conditions. The model can be used to predict future scenarios to prevent excessive monopile motions to occur, a (potential) tool for engineering purposes (determining workability)
Analysing the Relation Between Gaze Location and Gap Acceptance Decisions During Highway Merges
No full textBackground: Merging on a highway is a complex driving task that requires a lot of interaction with other road users. During these tasks, a driver is required to evaluate gaps in space and time between the themselves and other road users and obstacles in order to arrive at the right moment to merge onto the highway. To improve safety and increase road efficiency, it is necessary to understand the decision process during merging decisions. A way of achieving this, is to understand what visual information humans use during this decision process. This study investigated the relation between gaze location and gap acceptance decisions during highway merges.Methods: An experiment was performed in which 26 participants monitored an automated vehicle (AV) that was driving on a highway on-ramp. The participants were given the task to train the AV in whether or not to merge in front of an upcoming vehicle that was already driving on the highway. An eye tracker was used to measure gaze data, which was used to find the relation between gaze behaviour and decision outcomes and response times. A mixed-effects logistic model was used for a statistical analysis with decision outcomes as a dependent variable and different gap sizes as predictor variables. A mixed-effects linear model was used to find the relation between response times and dwell times and the different gap sizes and decision outcomes as predictor variables. For both the decision outcome and response time model, dwell time was later included to find the effect on the predictive validity.Results: The results show that a larger time and distance gap to the upcoming vehicle relate to a higher merging probability. For larger time gaps to the on-ramp, the probability of merging was found to be smaller. It was also found that time gaps to the end of the on-ramp significantly relate to response times, with an increase of 55ms per 1s. Larger time gaps to the upcoming vehicle significantly relates to larger response times, with an increase of 64ms per 1s. No significant relation was found between response time and distance gaps to the upcoming vehicle. The response time was found to be 0.60s longer for rejected gap decisions. The time gap to the end of the on-ramp significantly relates to dwell time, with an increase of 0.56% per 1s. The distance gap to the upcoming vehicle significantly relates to dwell time, with an increase of 0.60% per 10m. The time gap to the upcoming vehicle significantly relates to dwell time, with an increase of 0.52% per 1s. The presented results show as well that a significant relation exists between gaze behaviour and decision outcomes and response times. When analysing decision outcomes and response times, the interaction between dwell time and gap sizes should be taken into account. This improved the predictive validity of the used regression models.Conclusion: Several pieces of evidence suggest that gaze behaviour assist in understanding the human decision making process during merging. This study can serve as a basis for cognitive models that can investigate how the relation between gaze behaviour and gap sizes, decision outcomes and response times can help to understand and potentially predict gap acceptance decisions.Mechanical Engineering | Vehicle Engineering | Dynamics and Control
The Whale: Cultural centre Holesovice
No full textThe cultural centre will provide the city of Prague with a community centre combined with several large scale amenities (a cinema, a club, a big event hall and a skybar) to complement and, at the same time, relieve pressure on the inner city. The building is situated in a green, livable, accessible and diverse new area (outside of the clogged inner city) for both tourists and Praguers to experience and enjoy. Pedestrians are placed on a pedestal and find themselves in an unprecedented new inviting and exiting public space. The cultural centre will work on a city scale and a quarter scale. The goal should be to bring together different social groups. It will function as a community centre for the to be developed urban area as well as the existing neighborhoods (Letná and Holesovice). A place where they can meet, relax and use the wide variety of amenities. Concomitantly the building will give the Praguer an additional place to relax/go out during the weekend
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