Adapt-Ome

Insects provide spectacular examples of rapid diversification and high standing diversity. In particular, phytophagous insects often undergo remarkable radiations, making phytophagous lineages more diverse than their non-phytophagous counterparts. Diversification among phytophagous insects is likely to result from their tendency to specialize on certain host plant species. This specialization may induce host shifts and the evolution of new specialist races or species (through ‘ecological speciation’). Three components are necessary to ecological speciation: 1) a source of divergent selection, 2) a form of reproductive isolation, and 3) a genetic mechanism linking selection to reproductive isolation. The genes under selection and those conferring reproductive isolation may be one and the same (pleiotropy) or physically different (but statistically associated via linkage disequilibrium, LD). Points 1 and 2 have been thoroughly studied in various models. Other studies tackled the individual genetic mechanisms involved in host adaptation or in reproductive isolation .Yet, a more comprehensive view of the link between adaptation and isolation (i.e. point 3) is still lacking. Here we propose a study of the genomic mechanisms underlying the specialization of moth species (Ostrinia spp., Crambidae, Lepidoptera) to their host plants. The project will concern two closely related species, the European corn borer (ECB, Ostrinia nubilalis) and the Adzuki bean borer (ABB, Ostrinia scapulalis). The first feeds mainly on maize (Gramineae), while the latter develops on various dicotyledons. Gramineae feeders are scarce in the Ostrinia genus, and the maize was indeed introduced recently in Europe (500 years ago), i.e. in the native range of ECB, so that a host shift from dicotyledons to this gramineae is the most probable scenario. We intend to combine various observation levels and methodological approaches for an ambitious and comprehensive survey of these mechanisms. On one hand, we will apply population genomics, phylogeography and phylogenetics in natural populations of ECB and ABB (and for some tasks of the project in the Ostrinia genus, more broadly), to identify the genomic pattern of host specialization. On another hand, we will settle experimental populations of ECB and ABB on various hosts, to isolate the host effects from other environmental effects. These experimental populations will be the support for studying both genetic and regulatory (e.g. epigenetic) factors. While the first have been favoured in Evolution theory, because genes have long been considered as the ultimate targets of the evolution, the latter appear more and more as facilitators (or by contrast, as constraints) for genetic novelties to occur. These various observation levels and methodological approaches will be supported by the production of high-throughput genomic data owing to the recent advances in NGS (next generation sequencing) technologies. If these technologies induced a revolution for the study of non-model organism by giving access to up to now unimaginable amount of genomic data, we believe that they could also favor a shift in evolutionary concepts towards a more comprehensive view of the genetics of adaptation, including complex regulatory gene networks. The originality of the project likes in this will of reciprocal feedback between mechanisms and evolution. It indeed results from the fruitful rising collaboration between genomicists, population biologists and geneticists who compose the consortium of the project.