Pollen aggregation by viscin threads in Rhododendron varies with pollinator

Area of Science:

• Plant reproductive biology
• Evolutionary ecology
• Pollination biology

Background:

• Pollen grains can disperse individually or in aggregated groups.
• The role of pollinators in the evolution of pollen aggregation remains largely unexplored.

Purpose of the Study:

• To investigate whether pollinator interactions drive the evolution of pollen aggregation.
• To test the hypothesis that extensive pollen aggregation is favored when pollinators are scarce.

Main Methods:

• Quantified pollen aggregation variation (viscin threads) in 13 Rhododendron species.
• Assessed pollen removal per pollinator visit and pollinator visitation rates.
• Investigated functional pollinator groups based on grooming behavior.
• Sampled pollen deposited on stigmas in field conditions.

Main Results:

• Species pollinated by bees (high grooming) had less aggregated pollen compared to those pollinated by birds and Lepidoptera (low grooming).
• Bird- and Lepidoptera-pollinated species exhibited longer pollen-connecting threads, aggregating more pollen grains.
• Pollinator visitation frequency negatively correlated with pollen removal per visit, but not with stigma pollen loads.

Conclusions:

• Pollinator-mediated selection on pollen packaging strategies supports the hypothesis of floral evolution driven by pollen export.
• Pollen aggregation strategies appear to be shaped by pollinator grooming behaviors and visitation frequencies.