Insect bacterial symbionts and short term adaptation of aphids to abiotic and biotic stress

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Modern theories of evolution consider microbial symbionts of animals and plants as key mediators helping their host to adapt to rapid ecological change in their resources, natural enemies, and climatic conditions. We will use small insects called aphids and their parasitic wasps in controlled experiments, to test the hypothesis that aphids critically depend on the rapid evolutionary potential of their bacterial symbionts to survive to ecological stress that they face as part of their daily life on vascular plants used as their food and habitat. A well known species, the pea aphid, will be exposed to experimental evolution in distinct regimes of ecological stress imposed on them either as more or less virulent parasites, shifts between differently hospitable host plant species, or as a high temperature stress which they often face daily in hot summer while feeding on aerial plant parts. Four species of aphid bacterial symbionts among the best known to be maternally inherited in these aphids will be monitored closely using molecular techniques during the course of successive generations of stress, to document adaptive changes in the aphid bacterial community under particular stress regimes. Our findings should help to understand if aphids under stress respond quickly and adaptively to specific ecological threats, by modulating the size and composition of their bacteriome, which can be expected because of the fast rate of multiplication of bacteria compared to insects. Our study system is unique in bringing under scrutiny four levels of a natural terrestrial food web, where we will experiment with plants, small insect herbivores, their consortia of symbiotic bacteria, and parasitic wasps attacking them as natural enemies.