Transgenerational effect of inbreeding and Manduca sexta herbivory on defense-related traits in horsenettle (Solanum carolinense)

Plants have evolved diverse physical and chemical defenses against herbivores and pathogens.  While some of these defenses are expressed constitutively, others are induced only in response to specific challenges.  Inducible defenses allow plants to conserve resources in challenge-free environments, and to tailor defense responses to particular antagonists.  Recent evidence indicates that the induction of anti-herbivore defenses in one generation may influence the expression of such defenses in subsequent generations, which might provide progeny with a competitive advantage by conferring adaptations to local environmental conditions.  Research from my lab has explored the effects of population-level processes, including plant breeding system, on plant-insect interactions involving the perennial weed, horsenettle (Solanum carolinense). This work has documented significant inbreeding depression for herbivore resistance in horsenettle and has shown that inbreeding can compromise defense gene expression and the induction of physical and chemical defenses.  In this study, inbred and outcrossed genotypes of S. carolinense were subjected to either a damage treatment by Manduca sexta caterpillars or an undamaged treatment, and the progeny of these plants were assessed for anti-herbivore defense traits.  We predicted that the progeny of both outcrossed plants and plants exposed to herbivory will show greater anti-herbivore defense traits than their inbred and undamaged counterparts.  To test the hypothesis that both inbreeding and herbivory in one generation subsequently affects plant defense-related traits in the next generation, we measured the leaf trichome density of S. carolinense progeny and assessed M. sexta larval performance by measuring total leaf area consumed and larval relative growth rate on progeny grown from seeds of damaged and undamaged plants.