Abstract

Despite accelerating interest in the island syndrome, the evolutionary trajectories of island flowers remain poorly understood. Here, we derive a new dataset from the Southwest Pacific to evaluate how flower size evolves on islands. Specifically, we tested whether flowers with different pollination modes followed the island rule or evolved convergently toward gigantism or dwarfism. Results indicate that flower size follows the island rule. However, patterns differed significantly between pollination modes. Animal-pollinated flowers followed the island rule, while wind-pollinated flowers showed evidence for gigantism. Both of these trends were mirrored by evolutionary changes in flower-correlated traits. Overall, we provide the first test for an island syndrome in flower size and found that flowers with different pollination modes exhibited markedly different evolutionary trajectories. These results suggest that overall trends in the evolution of flower size on islands might be a byproduct of selection acting on flower-correlated traits.