Hierarchical constraints and trade-offs in the evolution of reproductive traits in neotropical myrtles

<jats:p>Flowers, fruits, and seeds form a developmental sequence in angiosperm reproduction, meaning that evolutionary changes in traits associated with one organ are expected to affect the others; yet these structures are rarely analyzed jointly at macroevolutionary scales. We here test whether evolutionary correlations among angiosperm reproductive traits reflect hierarchical constraints and allocation trade offs, and whether these relationships extend to evolutionary rates, using neotropical myrtles as a study case. We combined a comprehensive species-level dataset of floral, fruit, and seed traits with a large phylogeny of the group and evaluated alternative causal models using a set of phylogenetic comparative methods. We found strong support for a hierarchical organization of reproductive traits: flower size had a strong positive effect on fruit size, which in turn influenced seed size, while flower size also showed a direct positive effect on seed number. Clear size number trade offs were detected at both floral and seed levels. Evolutionary rates varied among traits, with fruits evolving faster than flowers and number-related traits evolving faster than size related ones. Seed evolutionary rates were strongly associated with fruit rates but not with flower rates, indicating partial decoupling among reproductive structures evolution. Together, these results indicate that reproductive trait correlations in angiosperms may arise from hierarchical constraints and allocation trade-offs. Despite floral conservatism, coordinated evolution between seeds and fruits persists, highlighting the importance of integrating multiple reproductive structures to understand the evolution of plant reproductive strategies.</jats:p>