Dispersal evolution in the angiosperms: the origin of heterocarpy (Visiting Scholar)
Dispersal determines gene flow among populations. In plants, dispersal is conditioned by fruit characteristics. The way fruits disperse away from an individual plant is always stochastic. This is in part because fruit morphology is not uniform, fruits with different attributes will reach farther or shorter away. However, some plants appear to have fruits specifically apt to reach particular distances, being those short or long. In some cases, several kinds of such fruits coexist in the same plant. This phenomenon is called 'heterocarpy', the production of several discrete fruit morphs of different form by a single plant. The different fruit morphs are often associated with differences in other reproductive traits, namely flower mating system and seed dormancy. The three syndromes (mating system, fruit shape and seed dormancy) are bet hedging mechanisms, and are expected to be under similar evolutionary constraints, although the evidence for this is contradictory. Heterocarpy thus constitutes an optimal system for the study of a) the emergence of threshold characters and b) the correlated evolution between dispersal and other traits. Theoretical models predict that heterocarpy can be a favorable strategy under heterogeneous environmental conditions. However, it is unclear how it can emerge, and how it did so in unrelated plat groups. I propose to synthesize the available information on heterocarpy and analyze its evolution. This will illustrate under which conditions discrete dispersal phenotypes emerge and how dispersal evolution interacts with the evolution of other important reproductive traits. Moreover, it will show what environmental conditions favor the different types of mating system, dispersal mechanism and seed dormancy.
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