Effects of pollen limitation on seed production in the pale pitcher plant (Sarracenia alata)

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Karis M. Kang, Biology, TCU, Fort Worth, TX and John D. Horner, Department of Biology, TCU, Fort Worth, TX

Background/Question/Methods
Pollen transfer among flowers contributes to the maintenance of genetic diversity and the stability and growth of plant populations through the production of seeds. Decreased pollen receipt can result in fewer offspring, a condition known as pollen limitation. We conducted field and laboratory experiments in a population of Sarracenia alata in Leon County, Texas to examine 1) the effect of floral herbivory by the pitcher plant moth, Exyra semicrocea, on pollen availability; and 2) the impact of pollen receipt on seed quantity and 3) seed quality.
To assess the effects of floral herbivory, we compared anther number and mass per flower between Exyra damaged flowers and undamaged flowers in April 2019. To assess pollen limitation, flowers were randomly assigned to a low pollen group (limited access to natural pollination), a control group (natural pollination), or a high pollen group (hand pollinated in addition to natural pollination). Seed count and mass were compared among treatments after ovary collection in September 2019. The effects of pollen limitation on seed quality were assessed by comparing 1) average mass of individual seeds for each treatment, and 2) differences in germination success among groups.
Results/Conclusions
Floral herbivory significantly decreased the number and mass of anthers in damaged flowers, and a high pollen load significantly increased the number of seeds produced compared to low-pollen and control flowers. Although pollen limitation occurred naturally during 2019 as indicated by low seed production in our control group, the small percentage of flowers damaged by herbivores in the overall study population indicates other causes, such as a reduced number of pollinators, may have contributed to pollen limitation in this species.
We found no differences in offspring quality among different pollen treatments based on individual seed mass or germination traits. Pollen limitation occurs in S. alata and may pose a conservation risk when combined with other ecological disturbances.