Multilevel variation in sugar profile of wild figs supports the dispersal syndrome hypothesis

Plant–frugivore mutualisms are shaped by suites of fruit traits that evolve in tandem with the preferences of seed dispersers, a concept encapsulated by the dispersal syndrome hypothesis. While morphological characteristics (e.g., size, color, firmness) have been extensively studied, the nutritional dimension, and particularly sugar profiles, remains comparatively understudied. This is despite its role as a primary reward influencing frugivore foraging decisions and despite the fact that these are the primary attractants driving animal feeding and ultimately seed dispersal. Here, we investigated the evolutionary and ecological drivers of sugar profile diversity in the ripe fruits of 15 animal-dispersed wild fig (Ficus) species. We sampled 1019 ripe fruit samples of 50 individual trees at 4 different field sites in Madagascar. Fruits were oven-dried and analyzed using High‑Performance Liquid Chromatography to quantify the abundances of sugars. We addressed three questions: (Q1) Are sugar-composition profiles species-specific? (Q2) Is the sugar profile phylogenetically conserved? (Q3) Do sugar profiles covary with other fruit traits in ways that support dispersal syndromes? Our results demonstrate fig species exhibit certain distinct sugar profiles, alongside substantial intraspecific variability; we did not find a phylogenetic signal in sugar profiles, suggesting that sugar profiles are not strongly constrained by shared ancestry but have likely diverged under ecological selection; and sugar profiles covary significantly with other fruit traits. Species with smaller fruits, different/multiple coloration, and mixed aromatic profiles rich in terpene and ester exhibited elevated sucrose concentrations, whereas larger, more conspicuous, and ester-rich fruits tended to contain higher fructose levels. Together, these findings lend support for the dispersal syndrome hypothesis by demonstrating that sugar profile, like other non-sugar traits, such as morphology, has evolved in association with frugivore preferences.