Print PagePollen viability in plants can be reduced post-developmentally by contact with sterilizing agents such as pollution, ultraviolet radiation and insect cuticular compounds, as well as pre-developmentally by genetic factors such as increased homozygosity resulting from inbreeding. While either pathway is roughly equivalent for plants in terms of reducing plant fitness, these pathways are potentially different in how they affect pollinators that depend on pollen for food. Pollen that fails early in development may shrivel and contain little or no cytoplasmic contents. Given that most pollen nutrients occur in the cytoplasm, this could greatly reduce pollen nutritional level for pollen consumers. Pollen viability is variable in Mimulus guttatus, but generally reduced by inbreeding. Using several maternal families and three crosses, we generated a range of pollen viabilities among individual plants and hand collected pollen to estimate pollen mass per flower and protein concentration per unit mass of pollen.
Results/Conclusions
We found that both protein concentration and pollen mass per flower declined sharply as viability declined. This indicates that factors that reduce pollen viability early in development have the potential for a cascade of impacts, including the reduction of male plant fitness, less nutrition for pollinators that use the pollen, and lower female plant fitness if pollinators avoid plants with lower pollen viability. Previous pollinator behavior work on Mimulus guttatus indicates that pollinators can discriminate against low-viability plants but that this discrimination may disappear when plants are in limited supply. Thus, inbreeding and other processes that reduce pollen viability likely hurt both plants and pollinators and the combination of both factors may hurt both entities still further.
