Nectary size is a pollination syndrome trait in Penstemon

Area of Science:

• Evolutionary Biology
• Plant Sciences
• Developmental Biology

Background:

• Floral syndromes are complex adaptations involving traits like color, nectar, and shape, crucial for pollinator interactions.
• In Penstemon, hummingbird-adapted flowers have repeatedly evolved from bee-adapted ancestors, with color and shape previously identified as key distinguishing traits.

Purpose of the Study:

• To investigate the evolutionary significance of nectar volume and nectary area in defining Penstemon pollination syndromes.
• To explore the developmental mechanisms underlying nectary size variation and its association with pollination syndromes.

Main Methods:

• Examined the evolutionary association between nectar volume, nectary area, and pollination syndrome across 19 Penstemon species.
• Assessed cellular processes (cell expansion and proliferation) influencing nectary size in selected species.
• Analyzed trait correlations (nectar volume, nectary area, stamen size) within a segregating population from an intersyndrome cross.

Main Results:

• Nectar volume and nectary area showed a significant evolutionary association with pollination syndrome in Penstemon.
• These nectar traits were correlated within a genetic cross, indicating a potential mechanistic link.
• Nectary area evolution involves parallel developmental processes, including cell expansion and proliferation.

Conclusions:

• Changes in nectary patterning, specifically nectary area, significantly contribute to the diversity of pollination syndromes.
• Repeated evolution of hummingbird adaptation in Penstemon is supported by parallel developmental processes affecting nectar production and nectary morphology.