Macroevolutionary patterns in seed component mass and different evolutionary trajectories across seed desiccation responses.

Seed coat and seed reserve show substantial mass variation, play different roles in plant life strategies and are shaped by different selective forces. However, remarkably little is known about the macroevolution of the relative allocation in seed components and its influence on important ecophysiological processes. Using phylogenetic comparative methods and evolutionary modelling approaches, we modelled mass changes in seed components along individual lineages for 940 species and compared the patterns across seed desiccation responses. Seed component allocation was driven primarily by changes in reserve mass rather than coat mass, as evolutionary rates in reserve mass significantly outpaced those in coat mass. Although the scaling patterns between reserve mass and coat mass were similar across desiccation responses, desiccation-sensitive seeds allocated more and evolved faster in reserve compared to desiccation-tolerant seeds. The findings emphasize the relative importance of reserve to coat in the evolution of plant reproductive strategies, revealing potential ecological advantages gained by enlarged reserve. As the first quantification of the evolutionary tempo and mode of seed component mass, our study allows a detailed interpretation of evolutionary pathways underlying seed storage behaviours and advances the understanding of the evolution of desiccation sensitivity in seeds.