The dispersal syndrome hypothesis: How animals shaped fruit traits, and how they did not

Fleshy fruits have evolved multiple times and display a tremendous diversity of colours, shapes, aromas and textures. For over a century this was attributed, at least in part, to frugivore-driven selection. The dispersal syndrome hypothesis posits that fruits and frugivores co-evolved, each exerting sufficient selective pressure on one another, and resulting to in suites of fruit traits that match frugivore behaviour, morphology and sensory capacities. In the last two decades of the past century, the dispersal syndrome hypothesis has been deemed overly adaptationist. Challenges are based on a variety of arguments, primarily that previous studies did not sufficiently incorporate a phylogenetic framework, and that non-adaptive factors can explain a great deal of extant fruit trait variation. In recent years, many studies have addressed these issues and found support for the dispersal syndrome hypothesis. As empirical evidence mounts, it's become increasingly clear that many fruit traits-primarily size, colour and scent-are strongly affected by frugivore trait preference. At the same time, many studies do not sufficiently consider the many confounding factors involved in fruit trait evolution. We review the evidence supporting the dispersal syndrome hypothesis and highlight the existing gaps in knowledge and the factors that are currently still not fully incorporated into the study of the evolution of fruit traits. A free Plain Language Summary can be found within the Supporting Information of this article.