LEVEY, D.J.; Univ. of Florida, Gainesville: It takes three to tango: How evolutionary interactions among microbes, fruits, and frugivorous vertebrates can help explain ethanol production.

Fruiting plants face an evolutionary dilemma: their fruits must be simultaneously attractive to seed-dispersing frugivores (vertebrates) and unattractive to non-seed-dispersing frugivores (microbes). Plant fitness is presumably tied to the ability of plants to solve this dilemma, whereas frugivore fitness is presumably tied to the ability of frugivores to exploit fruit pulp and circumvent plant defenses. Thus, production of any compound in fruit pulp should be viewed as the evolutionary endpoint of a complex three-way interaction among fruiting plants, microbes, and seed dispersers. More to the point, it’s likely simplistic to view ethanol production as a result of selection pressure by vertebrate frugivores or as a by-product of microbial fermentation. I will review alternative hypotheses for the evolutionary function of compounds in fruit pulp, focusing on ethanol. I will then summarize experimental trials with artificial fruits, microbes, and captive birds that illustrate the nutritional underpinnings of fruit rot (in the case of microbes) and fruit choice (in the case of birds). Finally, I will use these trials and the evolutionary theory that motivated them to champion the integration of microbial ecology, digestive physiology, and seed dispersal.