Trophic specialization and genetic structure in phytophagous insects

Selective pressures related to plant use determine that all herbivorous insects present some level of ecological specialization. The geographical distribution of plants influences the distribution as well as the ecological specialization of herbivorous insects; consequently, herbivore-plant interactions established at the local scale may influence conspecific population connections at local and regional scales. In this study, we investigated the variability and genetic differentiation of Tomoplagia (Diptera: Tephritidae) species, whose larvae develop in capitula of Asteraceae, mainly of the tribe Vernonieae. Based on previous surveys of their associations in different campos rupestres of the Espinhaço Mountain Range in Minas Gerais, this interaction was used to evaluate genetic differentiation in Tomoplagia both at local (among host plants) and at regional (within and/or among host plants from different localities) scales. Genetic variability of flies was measured with species-specific microsatellite markers which were isolated and characterized for species with different levels of ecological specialization: T. grandis (monophagous), and T. bicolor and T. incompleta (both oligophagous). The three species are not genetically structured between host plants or localities. Tomoplagia grandis showed weak to moderate genetic differentiation among localities, with no correlation with their parwise geographical distance. In contrast, T. bicolor and T. incompleta showed evidence of genetic differentiation at both local and regional scales; this differentiation was correlated with distance only in T. bicolor, whose host plants have greater beta diversity than hosts of T. incompleta. These results help to clarify mechanisms involved in genetic differentiation of herbivorous insects and provide the first approximation of the patterns of genetic differentiation in this group of herbivorous insects (AU)