SEED DISPERSAL IN VIOLA (VIOLACEAE): ADAPTATIONS AND STRATEGIES

Surveys of Viola dispersal mechanisms result in the distinction of two major adaptive syndromes: one purely myrmecochorous for the exploitation of seed-transporting ants, the other partially myrmecochorous (= diplochorous) for the explosive ejection of seeds followed by ant exploitation. Diplochory is exhibited by the majority of Viola species, but myrmecochory is exhibited only by eleven species with limited Eurasian distribution. Morphological and experimental evidence suggests the hypothesis that Viola is basically myrmecochorous but that different selective pressures, especially seed predation, have produced a clear divergence in dispersal systems. The majority of species, the diplochores, have evolved a system which combines ballistic and ant seed dispersal with predator avoidance. Diplochory itself may be a response to predation pressure. The minority of species are purely myrmecochorous, possibly highly coevolved with specific ant species, thus limiting the distribution of the Viola species concerned.