Dispersal mode of species influences the trypsin inhibitor levels in fruits

Proteinase inhibitors (PI) occur ubiquitously across microorganisms, plants, and animals and have been shown to inhibit "unwanted or foreign" proteolysis and to defend the host tissues against herbivore predation. In plants, PIs are found at very high levels in storage tissues such as tubers and fruits and are argued to serve as defense against herbivores. Recently, Pearce et al. showed that PI accumulation in wild tomato followed a parabolic pattern with age of the fruit; the PI level was low at early (2-3 weeks after anthesis) and late (ripened) stages of fruit growth, but very high at peak fruit growth. They suggested that such a pattern of accumulation may help deter premature dispersal of seeds by dispersers. In this paper, we extend this idea and argue that the dispersal mode of a species may strongly influence both the level and the temporal pattern of PI accumulation in its fruit. Analyzing the trypsin inhibitors, a major class of PI in 47 plant species representing various dispersal modes, we offer a test of this hypothesis.