jeudi 5 juillet 2018

Recherche de candidats pour une thèse financée - Lyon

Influence of symbionts on host niche and partner’s choices Context and objectives The processes underlying ecological speciation, i.e. the establishment of reproductive isolation between divergent populations, is a central question in Biology and has been at the origin of intense debates among evolutionary biologists. The fundamental question is to understand how reproductive isolation can emerge as a consequence of divergent selection despite gene flow. The idea that symbiosis could be a driver of speciation has been defended since the beginning of the 20th century. Symbiosis has been associated with major transitions in evolution, notably in insects, where, for example, the acquisition of nutritional obligate bacterial symbionts allowed phytophagous insects to feed on plant sap. In addition to obligate symbionts, insects are often associated with a diversity of facultative endosymbionts that can also play a role in the exploitation of the insect host niche and mating choice and could thus be associated with rapid diversification. The objective of this project is to investigate whether endosymbionts play a role in diversification and ecological speciation of insect pests, and most notably in their use of cultivated plants and partner’s choice. This study will be done on the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae), a complex of morphologically indistinguishable species, whose taxonomy has been the subject of important controversies. The most recent analyses, based on a threshold of 3.5% mitochondrial cytochrome oxidase 1 gene sequence divergence, have identified 28 species in this complex. This number has however to be taken with caution, as important mitochondrial variation is encountered in some “species”. Whiteflies harbour several bacterial symbionts: in addition to their obligate symbiont, 95% of B. tabaci individuals are infected by one or more facultative symbionts. Importantly, symbiotic composition is specific to each biotype and it is, in some cases, associated with particular biological and ecological features such as host plant range, geographical localisation and insecticide resistance. This raises the possibility that symbionts may play a role in the adaptation to environmental changes and the diversification of the B. tabaci species complex. Interestingly, B. tabaci biotypes differ in their capacity to transmit plant viruses, which seems to be linked to the composition of the bacterial symbiotic community they harbour, a hypothesis that needs further experimental evidence. Methodology Mate choice tests will be performed using males and females harbouring different associations of facultative symbionts. These same lines will also be used to measure insect attraction to different plants. Insect performance will be measured through the analysis of life history traits like survival, fecundity and metabolic capacities (by HPLC profiling of relevant metabolites). Molecular biology techniques will be used to determine the symbiont composition of the different insect lines. Skills This project implies manipulation of tiny (1mm) and fast moving insects, it thus requires a student having a strong interest in insect biology, and who possibly already worked on small insects. The recruited student should also show interest in behavioural ecology. Environment Experiments will be realised in two laboratories located at the same university site, University of Lyon (Villeurbanne, France), the Laboratory of Biometry and Evolutionary Biology (LBBE, UMR CNRS 5558, Université Lyon1) and the Laboratory of Functional Biology, Insects and Interactions (UMR INRA/INSA de Lyon 203 BF2I). The supervision will be done by members of these two laboratories, who are collaborating since several years and already supervised jointly students’ projects. The team ‘Genetics and Evolution of host-parasite interactions’ of the LBBE is recognized as a world leading group in the field of insect symbiosis, notably on the evolution of host-symbiont and symbiont-symbiont interactions. Its work on B. tabaci includes the evaluation of the diversity and effects of symbiotic communities. The team ‘Trophic SYMbioses’ of the BF2I lab has long-standing knowledge of nutritionally-based symbioses in insects. The team is internationally recognized for its expertise in the physiology and metabolism of symbiotic insects, working since several years on pea aphid / Buchnera aphidicola symbiotic system. The two teams belong to a multidisciplinary institute where bioinformatics, ecology, genetics and medicine are studied, providing a stimulating and rich environment. Supervision Laurence Mouton (laurence.mouton@univ-lyon1.fr), Federica Calevro (federica.calevro@insa-lyon.fr) References Romba R., Gnankiné O., Drabo SF., Tiendrebeogo F., Henri H., Mouton L. & Vavre F. Abundance of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) and its parasitoids on vegetables and cassava plants in Burkina Faso (West Africa). Ecology and Evolution. In press. Simonet P., Gaget K., Balmand S., Ribeiro-Lopes M., Parisot N., Buhler K., Duport G., Vulsteke V., Febvay G., Heddi A., Charles H., Callaerts P., Calevro F. (2018). Bacteriocyte cell death in the pea aphid/Buchnera symbiotic system. Proceedings of the National Academy of Sciences USA 2018 Feb 5. Pii: 201720237. doi: 10:10.1073/pnas.1720237115. Simonet P., Gaget K., Parisot N., Duport G., Rey M., Febvay G., Charles H., Callaerts P., Colella S., Calevro F. (2016) Disruption of phenylalanine hydroxylase reduces adult lifespan and fecundity, and impairs embryonic development in parthenogenetic pea aphids. Scientific Reports 6, 34321; doi: 10.1038/srep34321. Mouton L., Gnankiné O. Henri H., Terraz G., Ketoh G., Martin T., Fleury F. & Vavre F. (2015). Detection of genetically isolated entities within the Mediterranean species of Bemisia tabaci: new insights into the systematics of this worldwide pest. Pest Management Science, 71: 452-458. Mouton L., Gnankiné O., Henri H., Terraz G., Houndeté T., Martin T., Vavre F. & Fleury F. (2013). Distribution Bemisia tabaci biotypes (Homoptera: Aleyrodidae) and their associated symbiotic bacteria on host plants in western Africa. Insect Conservation and Diversity, 6: 411-421. Rabatel A., Febvay G., Gaget K., Duport G., Baa-Puyoulet P., Sapountzis P., Bendridi N., Rey M., Rahbé Y., Charles H., Calevro F., Colella S. (2013) Tyrosine pathway regulation is host-mediated in the pea aphid symbiosis during late embryonic and early larval development. BMC Genomics 14(1):235