Are seeds able to germinate before fruit color ripening? Evidence from six Neotropical bird-dispersed plant species

Many plants attract seed dispersers and indicate the presence of ripe, fleshy fruits with coloration changes. If seed maturation is simultaneous with visual signs for frugivorous, a portion of seeds can be removed before being ready for dispersal. In this study, we tested the delay visual signal hypothesis (DVSH), which implies high reproductive success when seed maturation precedes the visual signal of the fruit ripening, limiting the dispersal of unviable seeds. We evaluated this hypothesis with six tropical species that have fruits with discrete coloration for the immature, intermediate, and mature stages, testing the prediction that the development of mature and intermediate seeds is similar. First, we verified that the coloration of three categories was differentiable with color analysis. Next, we carried out germination and viability tests (i.e., electrical conductivity [EC] and tetrazolium) as an approach to evaluate the germination potential along development. We found that the EC of three species decreased constantly during fruit ripening, suggesting that the seed maturation is a gradual process, with a substantial germination of intermediate seeds. In the other species, the conductivity of seeds of fruits with intermediate coloration was lower than that of mature fruit, because mature seeds are more affected by predators and pathogens. The tetrazolium tests indicated that the viability of seeds of three species increased with maturity and smaller differences between intermediate and mature stages were observed, supporting the DVSH. Only two species achieved high percentages of germination, and for Myrcia splendens, the pattern was very consistent with the hypothesis. We concluded that the germination and viability rates of the seeds of each plant species depend on many factors (e.g., dormancy and time of exposure to predators); however, for all the species studied, there is some evidence that seeds can germinate before they reach maturity by color.