Chemical Ecology of Defence in Flowers and Leaves of the Solanaceae

Plants have evolved a range of defence strategies to protect themselves from herbivore attack. Defences can act either indirectly on the attacker, perhaps by attracting natural predators of the antagonist, or directly on the attacker by being toxic, however it is also known that defences can act negatively on pollinators resulting in pollinator deterrence. To reduce the effects of pollinator deterrence plants can rely on two evolutionary alternative mechanisms of defence: constitutive defences which are always present in the plant, and induced defence that is produced only when damaged is incurred by the plant. Much of the existing research into plant chemical defences focuses on leaf defences, despite the higher relative importance of flowers due to their role in reproduction, and there is a significant knowledge gap in the field of tissue-specific defence mechanisms in plants. The work detailed in this thesis work builds on previous research into the coevolution of plant mating system transitions to selfing and plant defence strategies, by incorporating analysis of both floral and leaf defences in populations and species of different mating systems within the Solanaceae. The first chapter of this thesis provides an introduction to plant-herbivore-pollinator interactions. In chapters two and three, I present a metabolomic and transcriptomic study using self-compatible and self-incompatible populations of the wild tomato species, Solanum pennellii, and provide evidence of mating system constraints on floral defence, and evidence of tissue-specific regulation of defence metabolites. The fourth chapter of this thesis provides a multispecies comparison of the floral and leaf defence metabolites in selfing and outcrossing species of three genera within the Solanaceae. The work presented here provides evidence for the convergent evolution of higher defences in flowers than in leaves, and evidence for adaptive phenotypic plasticity of leaf secondary metabolites when experiencing herbivory and an adaptive absence of plasticity in flower tissue. The results indicate that secondary metabolite production of herbivory-induced plants are tissue-specific, and may be mating system-specific in some taxa. To my knowledge, this thesis comprises one of the first comprehensive studies into the coevolution of plant mating system and defence strategies in both leaves and flowers, using comparative metabolomics and transcriptomics.