Macroevolution of a group of plant secondary defense compounds (pyrrolizidine alkaloids) in the dogbane and milkweed flowering plant family (Apocynaceae)

Plants are known to synthesize about 200,000 distinct secondary metabolites, chemical compounds that are not essential for their cellular metabolism. These plant secondary chemicals are important sources of medicines (e.g. aspirin), pesticides (e.g. pyrethrin), industrial compounds (e.g. latex), flavors (e.g. mint), and poisons (e.g. strychnine). To plants, these chemicals are essential defenses against herbivores, particularly insects. The efficacy of these defenses is not static over time, however, as herbivores adapt to their host plants defenses, evolving mechanisms to detoxify them or even co-opt them for their own defense against their predators. Thus a chemical that was once a valuable defense may become a liability, and its production lost. This project will investigate the evolution of a group of plant defense secondary compounds (pyrrolizidine alkaloids) in the dogbane and milkweed family (Apocynaceae). Plant secondary compounds in the Apocynaceae are diverse, with many having medicinal properties. Pyrrolizidine alkaloids in members of the Apocynaceae are highly toxic to non-adapted herbivores, but have little effect on specialist insects that store them within their tissues for defense against predators. Researchers will sample broadly across the Apocynaceae and reconstruct evolutionary relationships within the family using DNA sequence data. The resulting evolutionary tree will then be used as a framework to reconstruct the evolution of pyrrolizidine alkaloids within the group and better understand the relationship between these chemicals, the plants that produce them, and their herbivores. The research will provide new insights into evolutionary relationships within the medically important Apocynaceae plant family that can be used as a framework for broader questions within the family.