Does flower and fruit conspicuousness affect plant fitness? Contrast, color coupling and the interplay of pollination and seed dispersal in two Vaccinium species

Abstract

Pollinators and seed dispersers depend on flower and fruit colors as signals to mediate their interactions with plants. Signaling theory makes the general prediction that conspicuous signals will be selected because they increase detectability. However, direct evidence that conspicuous flower and fruit colors affect the fitness of plants in natural populations is scarce. Here, we test the prediction that conspicuous signals affect pollination and dispersal success in two plant species. We show that the prediction only holds true for flowers of one species, and propose that the widely accepted selection for conspicuousness may be oversimplifying. Moreover, the multiple functions of pigments in the protection against abiotic stressors could interfere with their signaling role to pollinating and seed-dispersing animals. Indeed, we find flower and leaf colors as well as fruit and leaf colors to be coupled, likely due to the involvement of pigments of flowers and epicuticular waxes of fruits in abiotic stress responses. Lastly, because plant reproduction is a multi-stage process in which the different steps may be uncoupled, we investigated whether differential fitness through selection of pollinators on flower conspicuousness in the pollination step is transmitted to the dispersal step to affect dispersal success. We show that this is partially true, with pollination success affecting the absolute, but not the proportional, dispersal success, and we highlight the importance of holistic approaches to plant signals in reproduction.