Differential ontogenetic effects of gut passage through fish on seed germination

Passage through the digestive tract of frugivorous vertebrates likely influences seed dormancy, time to germination, and/or future seedling growth. Effects of gut passage on seed germination have been extensively investigated among frugivorous birds and mammals, however, few studies have focused on frugivorous fish. Here we present the results of a feeding experiment focusing on a broadly distributed Amazonian frugivorous fish, Brycon falcatus, and a fig tree, Ficus gomelleira. We investigated the effects of gut passage and ontogeny on seed germination probability and speed. The probability of seed germination and germination speed increased for seeds defecated by fish relative to control seeds. We also detected a negative effect of intestine length, where germination probability and speed decreased when seeds passed through larger fish with greater intestine to body length ratio. Such effects are probably the result of ontogenetic diet shifts, in which young fish transition from carnivory to frugivory as adults; a process only revealed by the inclusion of both small juvenile and large adult individuals in our study. As such, we advance knowledge of the mechanisms involved in frugivory as a feeding habit among fishes and on animal-fruit mutualisms.