Heteromorphic stamens are differentially attractive in Swartzia (Fabaceae)

Area of Science:

• Plant-pollinator interactions
• Floral evolution
• Chemical ecology

Background:

• The division of labor hypothesis explains functional divergence in dimorphic stamens.
• Limited understanding exists regarding how stamen dimorphism affects pollinator attractiveness.
• Investigating visual and olfactory cues from distinct stamen types in Swartzia.

Purpose of the Study:

• To determine if dimorphic stamens in Swartzia species exhibit differential visual and olfactory attractants for pollinators.
• To analyze the role of UV reflectance, chromatic contrast, and volatile organic compounds in stamen attractiveness.

Main Methods:

• Field observations of anthesis dynamics and floral visitor activity.
• Spectrophotometric measurements of floral part reflectance, including UV spectra.
• Gas chromatography-mass spectrometry (GC-MS) analysis of volatile organic compounds (VOCs) from floral organs.

Main Results:

• Two distinct stamen sets were identified: smaller central and larger abaxial stamens.
• UV reflectance and chromatic contrast differed between stamen sets, notably in Swartzia simplex.
• Volatile profiles varied, with differences in aliphatic compounds, apocarotenoids, benzenoids, and sesquiterpene proportions between stamen types and species.

Conclusions:

• The two stamen types in Swartzia flaemingii and S. simplex possess distinct attractiveness properties.
• Differential visual and olfactory signaling contributes to varied pollinator attraction strategies.
• Findings highlight diverse mechanisms of attractiveness within stamen dimorphism and across Swartzia species.