of "Why are chiles hot? An integrative exploration of secondary metabolite function in ripe fruit"
Doug Levey and Joshua Tewksbury University of Florida
It is well known that the pungent compound in chile fruits, capsaicin, has many physiological effects in humans. Although it is widely used in medicine and is one of the most important spices in the world, the evolutionary basis for capsaicin remains mysterious. Why and how did the compound evolve? Is its function secondary (non-adaptive) or can its presence in chiles be explained by selective pressures of frugivores? Because similar secondary compounds are common in other fruits, our work will simultaneously address a long-standing paradox: Why do many plants place compounds in ripe fruit that are apparently toxic to fruit-eating animals? Six hypotheses for the role of secondary metabolites in ripe fruit, using chiles and capsaicin as a model system will be tested. The work will entail laboratory trials with captive frugivores and field studies on two chile species that are widely separated geographically and phylogenetically. One occurs in Arizona, the other in Boliva. In Boliva, a variety is available that is non-pungent (i.e., it lacks capsaicin). By comparing consumption of pungent and non-pungent chiles by a wide diversity of frugivores, from microbes to vertebrates, we will be able to determine the effect of capsaicin on frugivore behavior. Parallel studies will use artificial fruits made with and without capsaicin. These experiments will lead to a better understanding of capsaicin's evolutionary function and will pave the way for potential applications of capsaicin in human health, pest management, food storage, and chile cultivation.
