Divergence in inflorescence height: An evolutionary response to pollinator fidelity

Area of Science:

• Ecology
• Botany
• Evolutionary Biology

Background:

• Plant reproductive success is often mediated by animal pollinators.
• Interspecific interactions, such as shared pollination, can influence plant trait evolution.
• Floral height is a key trait that can affect pollinator visitation and plant reproductive isolation.

Purpose of the Study:

• To investigate the relationship between floral height similarity and shared pollinators in a subalpine meadow.
• To determine if plants sharing pollinators exhibit less variation in inflorescence height compared to those with different pollinators.
• To explore the potential role of pollinator fidelity in driving floral trait divergence.

Main Methods:

• Measured above-ground inflorescence heights for 8 wildflower species over two years in Colorado.
• Calculated an index of overlap for height distributions in pairwise species comparisons.
• Grouped species based on primary pollinators: long-tongued bumblebees, short-tongued bumblebees, hummingbirds, and solitary bees.

Main Results:

• Plant species sharing the same pollinators showed significantly smaller height overlap indices compared to species with different pollinators.
• This indicates that plants relying on the same pollinators tend to have more similar inflorescence heights.
• Conversely, plants with different pollinators exhibited greater variation in floral height.

Conclusions:

• Floral height similarity is associated with shared pollinators, supporting the hypothesis of selection for enhanced pollinator fidelity.
• The findings suggest that pollinator specificity can drive the evolution of floral traits, potentially reducing interspecific pollen transfer.
• Mechanisms involving pollinator flight patterns and interspecific visitation consequences are discussed as drivers of these observed height differences.