Secondary metabolite production and chemical adaptations in the class Ascidiacea

Ascidians are often abundant members of many benthic marine invertebrate communities in habitats characterized by intense predation and enormous competitive pressures. Numerous ecological observations suggest that these physically vulnerable invertebrates are generally unpalatable to potential predators and efficient competitors for available substrate. These observations, and the recent isolation of potent pharmacologically active secondary metabolites from taxonomically diverse ascidians, suggest that these compounds serve as efficient chemical defenses in this group of marine invertebrates. In this dissertation, the hypothesis that ascidian secondary metabolites may be effective chemical defenses against predation by potential fish and invertebrate predators is examined.; Taxonomically diverse ascidians are known to produce a great variety of novel secondary metabolites illustrating their biosynthetic plasticity. In this dissertation, investigations of the secondary natural products from 13 ascidian species from all three orders of the class Ascidiacea are described. This research resulted in the structural elucidation of 27 new ascidian metabolites, including 6 previously unreported and structurally unique classes of secondary metabolites. Thirteen compounds were isolated in sufficient quantities for use in feeding preference assays performed in situ with coral reef fishes and in flowing seawater laboratory aquaria in the laboratory with potential invertebrate predator of ascidians.; Results from these experiments, and correlating ecological observations for specific ascidians with a knowledge of the bioactive secondary metabolites in these ascidians, indicate that chemical defenses may be important survival strategies for all life stages of taxonomically diverse ascidians living in predator rich habitats.