Heterospecific pollen deposition in understory plants of a forest in central Amazon

Abstract

In co-flowering plant communities, pollinator movement can lead to the transfer of heterospecific pollen among species. This can affect the reproductive success of individuals, either by preventing conspecific pollen from reaching the stigma or by allelopathy, but little is known about this process in tropical areas. To analyze heterospecific pollen transfer and deposition, we investigated attributes related to pollinator attraction, such as corolla size, number of flowers per individual, floral arrangement, floral asymmetry, and distance from one flowering individual to another in a Central Amazon forest. The study was carried out in riparian plots of the Adolpho Ducke Forest Reserve during the rainy season. Stigmas and anthers were removed from all individual understory plants found in bloom in permanent plots. Slides were mounted with glycerinated gelatin, and all conspecific and heterospecific pollen grains were identified and counted. We then used a generalized linear mixed model framework to determine how the measured variables were related to the proportion of heterospecific pollen deposition (HPD) on stigmas. We found that the mean proportion of HPD in individuals was 4.7%, and 60% of individuals had no heterospecific pollen; from the 14 species studied, two had no heterospecific pollen. Species with wider flowers received less HPD, while species with more flowers per individual and with solitary flowers received more heterospecific pollen. Despite the significant variation in floral types in the Adolpho Ducke Reserve, there was a low percentage of heterospecific pollen deposition, probably due to specialized plant-pollinator interactions.