Chemical tradeoffs in seed dispersal: defensive metabolites in fruits deter consumption by mutualist bats

Abstract

Although fleshy fruits function primarily to attract seed dispersers, many animal‐dispersed fruits contain potentially toxic secondary metabolites. These metabolites can provide defense against seed predators and pathogens, but their effects on dispersers are still poorly understood. In some cases plants may experience a tradeoff, where the metabolites that provide fruit defense also reduce seed disperser preferences. In other cases the bioactivity of fruit secondary metabolites may be directed primarily at pests with no negative effects on seed‐dispersing vertebrates. We tested the effects of amides, a group of nitrogen‐based defensive compounds common in the plant genus Piper (Piperaceae), in interactions with the primary seed dispersers of Piper in the neotropics – fruit‐feeding bats in the genus Carollia (Phyllostomidae). In a series of flight cage experiments, pure amides and amide‐rich fruit extracts reduced the preferences of bats for Piper fruit, affecting both the bats’ initial choices to remove Piper infructescences and the proportion of fruit consumed from individual infructescences once they were removed. However, the effects of amides varied considerably among three species of Carollia and among the specific individual amides and extracts tested. Overall, our results support the hypothesis that plants experience a tradeoff between seed dispersal and fruit defense, but the strength of this tradeoff and the overall fitness consequences may depend strongly on ecological context.