High selfing capability and low pollinator visitation in the epiphyte Pitcairnia heterophylla (Bromeliaceae) at a Costa Rican cloud forest

Most epiphytic bromeliads exhibit specialized pollination systems likely to promote out-crossing but, at the same time, possess floral traits that promote autonomous selfing. Adaptations that promote selfing in flowering plants with specialized pollination systems have been considered as a mechanism for reproductive assurance. In this paper, we analyzed the breeding system and pollinator visitation rate of the hummingbird-pollinated bromeliad Pitcairnia heterophylla in order to see if they fit such trend. We performed hand pollination experiments, video recording of floral visitors, and recorded floral traits in order to describe the reproductive and pollination system of the studied species in a cloud forest in Costa Rica. Results from the pollination treatments indicated that P. heterophylla is self-compatible (SCIf = 0.77), capable of autonomous pollination (AFIf = 0.78), and non-agamospermous (AGf = 0.01). Floral traits, such as scentless red flowers, with tubular corolla and nectar production, suggested ornithophily which was confirmed by the video recording of Lampornis calolaemus (Trochilidae) visiting flowers. However, the visitation rate was low (0.6 visits day-1 per plant) based on 918 hours of video recording using trail cameras. We suggest that the high selfing capability of the studied population of P. heterophylla might be related to the low pollinator visitation rate. If low pollinator visitation is common among hummingbird-pollinated and epiphytic bromeliads, then selfing could be a widespread mechanism to enhance their reproductive success.

Quantitative importance of staminodes for female reproductive success in Parnassia palustris under contrasting environmental conditions

The five sterile stamens, or staminodes, in Parnassia palustris act both as false and as true nectaries. They attract pollinators with their conspicuous, but non-rewarding tips, and also produce nectar at the base. We removed staminodes experimentally and compared pollinator visitation rate and duration and seed set in flowers with and without staminodes in two different populations. We also examined the relative importance of the staminode size to other plant traits. Finally, we bagged, emasculated, and supplementary cross-pollinated flowers to determine the pollination strategy and whether reproduction was limited by pollen availability. Flowers in both populations were highly dependent on pollinator visitation for maximum seed set. In one population pollinators primarily cross-pollinated flowers, whereas in the other the pollinators facilitated self-pollination. The staminodes caused increased pollinator visitation rate and duration to flowers in both populations. The staminodes increased female reproductive success, but only when pollen availability constrained female reproduction. Simple linear regression indicated a strong selection on staminode size, multiple regression suggested that selection on staminode size was mainly caused by correlation with other traits that affected female fitness.Key words: staminodes, insect activity, seed set, spatial variation, Parnassia palustris.