Evidence for a Cost of Increased Floral Longevity in Female and Hermaphrodite Lobelia siphilitica (Campanulaceae)

Premise of research. Plants could respond to declines in pollination services by delaying floral senescence and thus increasing floral longevity. While a plastic increase in longevity could augment seed production by prolonging the opportunity for pollination, it could also reduce seed production if resources are allocated to floral maintenance rather than ovule maturation. However, this reduction in seed production could differ between females and hermaphrodites in gynodioecious species if more resources are required to maintain the larger corollas of hermaphrodite flowers.Methodology. To test whether increased longevity incurs costs of floral maintenance that reduce seed production, we manipulated the pollination of female and hermaphrodite Lobelia siphilitica flowers. We tested whether pollen receipt induces floral senescence, as expected if delayed pollination increases longevity, by measuring the days from corolla opening to wilting for unpollinated flowers and flowers pollinated on day 1 of the female phase. We then tested whether increased longevity reduces seed production by hand-pollinating female and hermaphrodite flowers on day 1 or day 5 of the female phase and counting seeds per fruit.Pivotal results. Relative to the corollas of unpollinated flowers, the corollas of pollinated flowers senesced 50% earlier for females and 14.4% earlier for hermaphrodites. Increased longevity reduced seed production by 34.1%, but there was no difference in the magnitude of this reduction between females and hermaphrodites.Conclusions. Our results suggest that L. siphilitica could respond plastically to declines in pollination services by increasing floral longevity but that this increase incurs costs of corolla maintenance that reduce the seed production of both females and hermaphrodites. Consequently, whether plasticity in longevity can help plants maintain seed production as pollinators decline will depend on whether the resource costs of floral maintenance are outweighed by the benefits of a prolonged opportunity for pollination.

Automated summary

Plants can respond to declines in pollination services by increasing floral longevity, but this may lead to a reduction in seed production due to higher costs of floral maintenance. The reduction in seed production is similar for females and hermaphrodites in gynodioecious species.