Reconstructing an historical pollination syndrome: keel flowers

Area of Science:

• Evolutionary Biology
• Plant Science
• Ecology

Background:

• Keel flowers are characterized by bilateral symmetry, specific petal arrangements, and enclosed reproductive organs.
• The Fabaceae (Leguminosae) family is known for its diverse species and the presence of keel flowers.
• This study investigates the evolutionary relationship of keel flowers between Fabaceae and Polygalaceae within the order Fabales.

Purpose of the Study:

• To explore the evolutionary origins of keel flowers in the order Fabales.
• To determine if the evolution of keel flowers in Fabaceae preceded and influenced their evolution in Polygalaceae.
• To investigate the role of pollinator pressure and mimicry in the convergent evolution of keel flowers.

Main Methods:

• Phylogenetic analysis of 678 taxa using plastid gene regions (matK, rbcL, trnL).
• Molecular dating to establish temporal origins of keel flowers.
• Ancestral area and ancestral state reconstructions to infer spatial and trait evolution.

Main Results:

• Keel flowers originated multiple times within angiosperms, likely driven by pollinator specialization (bees).
• The evolution of keel flowers in Polygaleae coincided with the widespread distribution of keel-flowered Papilionoideae (Fabaceae).
• Early Polygaleae keel flowers exhibited functional morphology similar to existing Papilionoideae keel flowers, suggesting pollinator exploitation.

Conclusions:

• Multiple origins of keel flowers in Fabales suggest convergent evolution driven by pollinator pressure.
• Findings support the hypothesis that keel-flowered Polygaleae exploited pollinators of existing keel-flowered Fabaceae species.
• The study provides evidence consistent with mimicry driving the evolution of the keel flower pollinator syndrome in Fabales.