Plasticity in floral longevity and sex-phase duration of Lobelia siphilitica in response to simulated pollinator declines

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.