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Koella, Jacob
Nom
Koella, Jacob
Affiliation principale
Fonction
Professeur.e ordinaire
Email
jacob.koella@unine.ch
Identifiants
Résultat de la recherche
Voici les éléments 1 - 2 sur 2
- PublicationAccès libreAdaptation of mosquitoes to climate change and its impact on the transmission of a vector-borne pathogen(2023)
; Avec l'augmentation des températures moyennes mondiales, les maladies à transmission vectorielle telles que le paludisme, la dengue ou le Zika sont susceptibles de connaître des changements de prévalence, d'intensité et de répartition géographique. Cela est largement dû à la dépendance à la température à la fois des moustiques et des parasites. Étant donné que les moustiques sont des ectothermes, la plupart de leur développement et de leur physiologie sont fortement influencés par la température. De plus, en raison de la biocinétique des enzymes, la performance thermique des insectes est généralement non linéaire et décalée vers la gauche autour d'un optimum. Par conséquent, de très petites variations vers des températures plus chaudes peuvent avoir des effets dramatiques. Jusqu'à présent, la plupart des études décrivant la relation entre les moustiques, la transmission par les moustiques et la température ont examiné les différences phénotypiques dans les traits de l'histoire de vie et la transmission basée sur des expériences à court terme. Cependant, le changement climatique est un processus à long terme qui laisse aux moustiques le temps de s'adapter aux nouvelles conditions environnementales. Dans cette thèse, nous avons cherché à étudier le potentiel d'adaptabilité du moustique tigre africain, Aedes aegypti, aux températures changeantes. Dans les deux premiers chapitres de cette thèse, nous évaluons et discutons de l'influence de l'acclimatation thermique sur différentes branches du système immunitaire du moustique. Dans les trois chapitres suivants, nous utilisons une approche évolutive pour étudier l'impact de l'adaptation thermique sur plusieurs aspects de la capacité vectorielle du moustique. En élevant des moustiques pendant plusieurs générations à quatre températures différentes - 24°C, 26°C, 28°C et 30°C -, nous avons créé 12 lignées adaptées à ces températures. Dans le chapitre 3, nous évaluons l'impact de l'adaptation thermique en mesurant la réponse thermique de nos lignées en ce qui concerne leur développement larvaire, leur taille corporelle adulte et leur longévité. Dans le chapitre 4, nous évaluons leur réponse antibactérienne et leur compétence pour la dengue à différentes températures. Et dans le chapitre 5, nous mesurons la préférence thermique des lignées adaptées au froid et au chaud. Les résultats de ces expériences et leurs implications pour l'épidémiologie des maladies vectorielles dans un climat changeant sont discutés tout au long de la thèse. Dans l'ensemble, ce travail offre une compréhension plus large de l'impact du réchauffement climatique sur la biologie thermique des moustiques et souligne la nécessité de prendre en compte les changements évolutifs pour effectuer des prédictions fiables. ABSTRACT With rising global mean temperatures, mosquito-borne disease such as malaria, dengue or Zika are prone to experience shifts in prevalence, intensity, and geographical range. This is largely due to the temperature dependence of both the mosquitoes and the parasites. Since mosquitoes are ectotherm, most of their development and physiology are strongly affected by temperature. And because of the biokinetics of enzymes, the thermal performance of insects is typically non-linear and left-skewed around an optimum. Consequently, very small shifts towards warmer temperatures can have dramatic effects. So far, most studies that described the relationship between mosquitoes, mosquito-borne transmission and temperature have been looking at phenotypic differences in life-history traits and transmission based and short-term experiment. But climate change is a long-term process that gives mosquitoes time to evolve to new environmental conditions. In this thesis, we’ve sought to investigate the potential of adaptability of the African tiger mosquito, Aedes aegypti, to changing temperatures and its underpinnings. In the first two chapters of this thesis, we evaluate and discuss how thermal acclimation influences different branches of the mosquito’s immune system. In the following three chapters, we use an evolutionary approach to investigate the impact of thermal adaptation on several aspects of mosquito’s vectorial capacity. By rearing mosquitoes over several generations at four different temperatures- 24°C, 26°C, 28°C and 30°C-, we’ve created 12 temperature-adapted lines. In chapter 3, we assess the impact of evolutionary thermal adaptation by measuring the thermal response of our lines regarding their larval development and adult body size and longevity. In chapter 4, we evaluate their anti-bacterial response and competence for dengue at different temperatures. And in chapter 5, we measure the thermal preference of cold and warm-adapted lines. The results of these experiments and their implication for the epidemiology of vector-borne diseases in a changing climate are discussed throughout the thesis. Overall, this work provides a broader understanding of the impact of climate warming on the thermal biology of mosquitoes and highlights the need to consider evolutionary changes to make reliable predictions. - PublicationAccès libreThe role of oxidative stress in senescence and immune responses of the mosquito "Aedes aegypti"Oxidative stress arises from an imbalance between the production of free radicals and the body's capacity to counteract them with antioxidants. An excess of free radicals can lead to damage in various cellular components. Initially, free radicals were considered inherently toxic, and given their presence throughout Earth's history, Harman proposed that the accumulation of oxidative damage over time was the fundamental mechanism behind senescence (ageing). However, this theory relied heavily on evidence from studies comparing data across different species. As studies began to manipulate free radical production and antioxidant defences within the same species, contradictory results emerged. Consequently, we adopted an evolutionary approach to explore whether the accumulation of oxidative damage could account for senescence within a species where two populations had been selectively bred for varying lifespans. Regrettably, our experiment did not yield direct support for the free radical theory of ageing. The long-living mosquito lines did not exhibit significant differences in oxidative damage levels compared to the short-living lines. Nevertheless, our investigation revealed that mosquitoes with longer lifespans had lower levels of reactive oxygen species (ROS) and higher levels of antioxidant defences, resulting in a superior redox potential. This suggests that rather than oxidative damage, an individual's ability to maintain the balance between free radical production and antioxidant defences throughout its life may be the primary driver of senescence. Additionally, recent discoveries have unveiled the beneficial roles of ROS, which are essential for normal cellular metabolism. This paradigm shift led to a reevaluation of the role of free radicals in biology. We now understand that they are involved in several critical biological processes, such as cell proliferation, mobility, signalling, immunity, and more. However, it is crucial to recognize that while ROS play essential roles, they must be maintained within a narrow concentration range for their benefits to manifest. When employing them in their metabolic processes, organisms require effective defences against excessive ROS. Hence, our research aims to elucidate the role of antioxidant defences in the immune response of Aedes aegypti mosquitoes against the microsporidia parasite Vavrai culicis. Our study supports previous findings that ROS are vital for resistance against the parasite, and we also observed that individuals with higher levels of glutathione have a reduced probability of being infected by the parasite. Therefore, mosquitoes must produce ROS in sufficient quantities to have an effective immune response and possess robust antioxidant defences. Finally, we investigated whether oxidative stress could be a mechanistic link in trade-offs between various life history traits. We examined whether males' susceptibility to oxidative stress influences the cost of reproduction and whether intrasexual competition drives this trade-off. Our results demonstrated that male Aedes aegypti mosquitoes experienced higher mortality rates, reduced tolerance to bacterial infection, and increased oxidative damage when residing in a group dominated by females (24 females / 8 males). This suggests that oxidative stress is associated with the trade-off between reproduction and survival. However, the primary driver of this trade-off appears to be the act of mating itself, possibly due to the proteins males must transfer to females during copulation. In conclusion, our thesis emphasizes that merely assessing oxidative damage is insufficient to comprehend the role of oxidative stress in various life history traits. What holds greater significance is the maintenance of a delicate equilibrium between free radical production and antioxidant capacity throughout an organism's lifespan. This equilibrium seems to drive the emergence and evolution of diverse life history traits and tradeoffs.