Premise: Pollinator declines can reduce the quantity and quality of pollination services, resulting in less pollen deposited on flowers and lower seed production by plants. In response to these reductions, plants can increase the opportunity for pollination by plastically adjusting their floral traits, including floral longevity and sex-phase duration. However, studies of plant responses to pollinator declines have primarily focused on floral evolution across generations rather than plasticity in floral traits within a generation.

Methods: To test whether plants can respond to pollinator declines by plastically adjusting their floral traits, we simulated declines by experimentally reducing pollinator access to Lobelia siphilitica plants, and measuring floral longevity and male- and female-phase duration. We also measured daily display size and phenotypic gender to test whether plasticity in floral longevity and sex-phase duration affected inflorescence traits.

Results: We found that experimentally reducing pollination extended the male-phase duration of early-season flowers and the longevity of late-season flowers. However, plants with an extended male phase did not have a more male-biased phenotypic gender, and plants with an extended floral longevity did not have a larger daily display.

Conclusions: Our results suggest that L . siphilitica plants can respond to pollinator declines by plastically adjusting both the longevity and sex-phase duration of their flowers. Consequently, plasticity in floral traits could be one mechanism by which plants respond to decreases in pollination services caused by pollinator declines.

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