Evolutionary consequences of flowering-pollinator asynchrony: the case of a floral oil-producing plant and its oil-collecting bees.

Background and aims: Selective pressures, such as biotic interactions, can fluctuate over reproductive seasons, influencing trait-fitness relationships and, consequently, selection outcomes. Phenological asynchronies between plants and pollinators within a single flowering season exemplify how such interactions vary on short timescales, potentially affecting the fitness function of plant populations. However, the role of discontinuous temporal overlap between flowering and pollinator activity in driving the adaptive evolution of floral traits remains poorly understood.

Methods: In this study, we examined the variation of plant-pollinator temporal overlap within a population of the floral oil-producing Stigmaphyllon paralias (Malpighiaceae) to estimate trait-fitness (flower size-total fitness) relationships and the resulting selection pattern. We also assessed pollen limitation and pollinator-flower size association.

Key results: Our findings indicate that plant-pollinator asynchrony led to differential pollen limitation between peak- and late-flowering plants, contributing to correlational selection on flower size and flowering time. Peak-flowering individuals exhibited a positive flower size-fitness relationship under high pollen limitation, while this association was negative for late-flowering individuals under low pollen limitation, likely due to resource allocation effects. Despite these dynamics, overall selection was non-significant, although the probability of pollinator visitation increased with flower size.

Conclusions: These results underscore the potential for fluctuating pollinator selective pressures within a single reproductive season to influence floral adaptation. Specifically, they reveal strong differences in flowering-pollinator synchrony that drive selection outcomes, which may help stabilize genetic and phenotypic variation and potentially prevent rapid trait evolution.