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Herbivores have evolved distinct strategies to cope with plant defenses prior to becoming a pest. Some evolved resistance to toxic compounds; others suppress host toxin production. These traits seem to co‐occur within herbivore species, particularly among spider mites, which are major pests in many crops. The intraspecific variation within the spider mites is a model for adaptive pest evolution on crops such as tomato. Empirical data collected from nonsolanaceous wild host plants suggest that natural populations predominantly comprise individuals capable of inducing tomato defenses, while a small proportion suppress these defenses. Additionally, resistant individuals are observed only rarely within these populations. This study aimed to investigate the presence of these traits within populations adapted to tomato plants. Here, Tetranychus urticae populations sampled from tomato at three field sites were compared. To discriminate between mites that induce/suppress defenses and to assess their degree of resistance, the magnitude of induced defenses was measured and aligned with oviposition data. The expression of effector 84 was also assessed to determine whether its magnitude of expression is a good predictor of suppression with the magnitude of suppression. Surprisingly, we observed that suppression is the dominant phenotype in mite populations collected from field‐grown tomatoes. Our results suggest that suppression may be rare only at the beginning of an herbivore's adaptive trajectory after colonization of a novel host but may rapidly become common due to natural selection. This suggests the possibility that suppression potentially represents a prevalent phenotype among host‐adapted herbivores and, consequently, among pests. The intraspecific variation within the spider mites is a model for adaptive pest evolution on crops such as tomato. Here, Tetranychus urticae populations sampled from tomato at three field sites were compared, revealing that suppression is the dominant phenotype in mite strains collected from field‐grown tomatoes. It seems that suppression may be rare only at the beginning of an herbivore's adaptive trajectory after colonization of a novel host but may rapidly become common due to natural selection, implying that suppression may be a common phenotype among host‐adapted herbivores and consequently among pests.

Laboratory studies are often criticized for not being representative of processes occurring in natural populations. One reason for this is the fact that laboratory populations generally do not capture enough of the genetic variation of natural populations. This can be mitigated by mixing the genetic background of several field populations when creating laboratory populations. From these outbred populations, it is possible to generate inbred lines, thereby freezing and partitioning part of their variability, allowing each genotype to be characterized independently. Many studies addressing adaptation of organisms to their environment, such as those involving quantitative genetics or experimental evolution, rely on inbred or outbred populations, but the methodology underlying the generation of such biological resources is usually not explicitly documented. Here, we developed different procedures to circumvent common pitfalls of laboratory studies, and illustrate their application using two haplodiploid species, the spider mites Tetranychus urticae and Tetranychus evansi. First, we present a method that increases the chance of capturing high amounts of variability when creating outbred populations, by performing controlled crosses between individuals from different field‐collected populations. Second, we depict the creation of inbred lines derived from such outbred populations, by performing several generations of sib‐mating. Third, we outline an experimental evolution protocol that allows the maintenance of a constant population size at the beginning of each generation, thereby preventing bottlenecks and diminishing extinction risks. Finally, we discuss the advantages of these procedures and emphasize that sharing such biological resources and combining them with available genetic tools will allow consistent and comparable studies that greatly contribute to our understanding of ecological and evolutionary processes. Here, we detail methodologies to create outbred and inbred populations for laboratory studies in haplodiploids. Additionally, we provide an experimental evolution protocol, which allows reducing the risks of losing experimental populations. Finally, we outline the advantages of such methodologies and we emphasize that combining these biological resources with available genetic tools will allow consistent and comparable studies among laboratories using the same organisms.

Rising temperatures due to climate change are predicted to accelerate the life cycle of arthropod herbivores thereby exacerbating pest formation. Notorious pests like spider mites thrive in areas with high temperatures (32–35 °C), and it is predicted that the size and number of such areas will expand in the coming decades. Higher temperatures can directly accelerate population growth, but also indirectly affect them through changes in the plant's defensive mechanisms. Spider mites have been shown to adapt to plant defences, with natural selection favouring defence-suppressing traits. However, it is not known to what extent suppression is affected by rising temperatures and how this might tie into the rate of adaptation and pest damage. In this study, we investigated the effect of two temperatures (25 °C and 32 °C), on the spider mite–tomato interaction, predicting the influence of rising temperatures on favouring defence-adapted mites. We found that all mite strains caused more plant damage at 32 °C, but temperature did not affect the overall patterns of induction and suppression of defence genes. Although fecundity was higher for all strains at 32 °C, juvenile and adult survival was lower, especially for inducer mites. With these data, we parametrized population models for the two strains over three months, indicating that suppressor mites might displace inducers at the higher temperature, either when it is constant or in the form of heat waves. Our models predict that in areas with higher temperatures, defence-suppressing mites are favoured, which will accelerate and consequently spur pest formation.

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. urticaeinducer 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.

Laboratory studies are often criticized for not being representative of processes occurring in natural populations. This can be partially mitigated by using lab populations that capture large amounts of variation. Additionally, many studies addressing adaptation of organisms to their environment are done with laboratory populations, using quantitative genetics or experimental evolution methodologies. Such studies rely on populations that are either highly outbred or inbred. However, the methodology underlying the generation of such biological resources are usually not explicitly documented. Given their small size, short generation time, amenability to laboratory experimentation and knowledge of their ecological interactions, haplodiploid spider mites are becoming a widely used model organism. Here, we describe the creation of outbred populations of two species of spider mites, Tetranychus urticae and T. evansi, obtained by performing controlled crosses between individuals from field-collected populations. Subsequently, from the outbred population of T. evansi, we derived inbred lines, by performing several generations of sib-mating. These can be used to measure broad-sense heritability as well as correlations among traits. Finally, we outline an experimental evolution protocol that can be widely used in other systems. Sharing these biological resources with other laboratories and combining them with the available powerful genetic tools for T. urticae (and other species) will allow consistent and comparable studies that greatly contribute to our understanding of ecological and evolutionary processes.

Plants have evolved several defensive strategies (e.g. secondary metabolites, wound-inducible proteins) to limit the damage caused by herbivory. However, some herbivores have evolved means to circumvent such plant defences. Indeed, while most herbivores trigger plant defences, some can suppress or even down-regulate them, and examples of this strategy have been mainly reported in herbivores interacting with plants from the Solanales order. Unlike Tetranychus urticae, a polyphagous spider-mite species that induces wound-responses on tomato plants, T. evansi and T. ludeni, specialists of the Solanaceae family and the Solanales order, respectively, can down-regulate such defences. However, little is still known about the defence targets of this manipulative ability. By using tomato plants with impaired defences, results shown that T. evansi and T. ludeni may manipulate similar defence targets. Additionally, to further understand how broad this down-regulation ability is and how different degrees of specialization (host range) can influence its presence and intensity down-regulation, four plants from the Solanales order, namely tomato, datura, tobacco and purple (three Solanaceae and one Convolvulaceae), and bean plants (Fabales: the outgroup) were selected. It was observed that T. evansi and T. ludeni were locally adapted to tomato and purple plants, respectively, and that T. urticae performed worse in Solanales order plants than in the outgroup. Moreover, no evidences of down-regulation were found contrarily to what was expected. Indeed, only suppression of plant defences was observed, being present for the three mite species on at least one of the five plants tested. Finally, to understand what may be the ecological consequences of down-regulation, choices between plants either clean or pre-infested with T. evansi and T. urticae were performed. This experiment revealed that, despite the benefits of down-regulation, spider mites preferred plants pre-infested with T. urticae. With this project, it was shown that the manipulation of plant defences is highly dependent on both host and herbivore, but not on the degree of specialization of the latter. As such, a co-evolutionary approach of this complex phenomenon can be the key to understand the evolution of defence manipulation.

Panicum maximum cultivars have distinct characteristics, especially morphological ones related to the leaf structure and coloration, and there may be differences in the spectral behavior captured by sensors. These differences can be used in classification using machine learning (ML) algorithms to differentiate biodiversity within the same species. The objectives of this study were to identify ML models able to differentiate P. maximum cultivars and determine which is the best spectral input for these algorithms and whether reducing the sample size improves the response of the algorithms. The experiment was carried out at the experimental area of the Forage Sector of the School Farm belonging to the Federal University of Mato Grosso do Sul (UFMS). The leaf samples of the cultivars Massai, Mombaça, Tamani, Quênia, and Zuri were collected from experimental plots in the field. Analysis was carried out on 120 leaf samples from the P. maximum cultivars using a VIS/NIR hyperspectral sensor. After obtaining the spectral data and separating them into bands, the data were submitted for ML analysis to classify the cultivars based on the spectral variables. The algorithms tested were artificial neural networks (ANNs), REPTree and J48 decision trees, random forest (RF), and support vector machine (SVM). A logistic regression (LR) was used as a traditional classification method. Two input models were evaluated in the algorithms: the entire spectrum band provided by the sensor (ALL) and another input configuration using the calculated bands. The reflectances from the P. maximum cultivars showed different behavior, especially in the green and NIR regions. RL and ANN algorithms using all information in the spectrum are able to accurately classify the cultivars, reaching accuracies above 70 for CC and above 0.6 for kappa and F-score. VIS/NIR leaf reflectance can be a powerful tool for low-cost, non-destructive, and high-performance analysis to distinguish P. maximum cultivars. Here, we achieved better model accuracy using only 40 leaf samples. In the present study, the J48 decision tree model proved to have good classification performance regardless of the sample size used, which makes it a strategic model for forage cultivar classification studies in smaller or larger datasets.

Potassium (K) is essential for the productivity of tropical grasses, but its optimal supply remains unclear. This study evaluated the effects of K on gas exchange, photosynthetic rate (A), forage production (FP), and root development (RP) in Panicum maximum cultivars. The experiment was conducted using a randomized block design in a 6 × 4 factorial scheme (six cultivars: Tanzânia, Quênia, Mombaça, Zuri, Massai and Tamani; and four K rates: 0, 205, 410 and 820 mg dm −3 ). There was interaction between cultivars and K rates for A and stomatal conductance (g s ), with linear increases in A for all cultivars. The g s response in the Zuri cultivar was quadratic, with a maximum of 5.32 mmol m −2  s −1 at the dose of 410 mg dm −3  K, and linear for the other cultivars. The CO 2 concentration (Ci) and leaf temperature (Tleaf) were not influenced by the K dose or by the cultivars, maintaining an average of 129.28 ppm and 29.32 °C, respectively. Transpiration (E) increased by 0.018 mmol m −2  s −1 with increasing K doses. The chlorophyll content fitted a quadratic model, with a maximum of 35 SPAD at the dose of 530 mg dm −3 . The FP increased linearly for all cultivars, with the highest FP in the cultivars Quênia, Mombaça and Zuri. Increasing K doses improved A and g s , reflecting in higher FP. The cultivars Quênia and Mombaça showed the greatest increases in FP up to 820 mg dm −3  K, while the maximum efficiency for RP occurred between 205 and 410 mg dm −3 , suggesting that excessive K supply may not proportionally increase root development.

The Pantanal is the world’s largest and most biodiverse continental sheet-flow wetland. Recently, vast tracts of the Pantanal have succumbed to the occurrence of fires, raising serious concerns over the future integrity of the biodiversity and ecosystem services of this biome, including revenues from ecotourism. These wildfires degrade the baseline of natural ecosystems and the ecotourism economy across the region. Local residents (“Pantaneiros”) anecdotally state that extensive cattle herbivory can solve the contemporary flammability problem of the Pantanal by controlling vegetation biomass, thereby preventing or reducing both fuel loads and fires across the region. Here, we examine the covariation between the presence and density of cattle and the incidence of fires across the Brazilian Pantanal. Variables assessed included bovine cattle density, SPI (Standardized Precipitation Index), GPP (Gross Primary Productivity)/biomass estimate, and fire foci along a 19-year time series (2001 to 2019). Our findings show that fire foci across the Pantanal biome are related to climatic variables, such as lower annual precipitation and higher annual drought indices (SPI) rather than to cattle stocking rates. Therefore, the notion of “cattle firefighting”, a popular concept often discussed in some academic circles, cannot be validated because cattle numbers are unrelated to aboveground phytomass. Gross primary productivity further invalidated the “cattle herbivory” hypothesis because GPP was found to be strongly correlated with cattle density but not with the spatial distribution of fires. Fires throughout the Pantanal are currently aggravated by the presence of livestock and result from a combination of extreme weather events and outdated agricultural practices.