Seed dispersal syndrome predicts ethanol concentration of fruits in a tropical dry forest

Studying fruit traits and their interactions with seed dispersers can
improve how we interpret patterns of biodiversity, ecosystem function, and
evolution. Mounting evidence suggests that fruit ethanol is common,
variable, and may exert selective pressures on seed dispersers. To test
this, we comprehensively assess fruit ethanol content in a wild ecosystem
and explore sources of variation. We hypothesise that both phylogeny and
seed dispersal syndrome explain variation in ethanol levels, and we
predict that fruits with mammalian dispersal traits will contain higher
levels of ethanol than those with bird dispersal traits. We measured ripe
fruit ethanol content in species with mammal- (n = 16), bird- (n = 14), or
mixed-dispersal (n = 7) syndromes in a Costa Rican tropical dry forest.
Seventy-eight percent of fruit species yielded measurable ethanol
concentrations. We detected a phylogenetic signal in maximum ethanol
levels (Pagel’s λ = 0.82). Controlling for phylogeny, we observed greater
ethanol concentrations in mammal-dispersed fruits, indicating that
dispersal syndrome helps explain variation in ethanol content and that
mammals may be more exposed to ethanol in their diets than birds. Our
findings further our understanding of wild fruit ethanol and its potential
role as a selective pressure on frugivore sensory systems and metabolism.