Selection on spur shape in Impatiens capensis.

Area of Science:

• Ecology
• Evolutionary Biology
• Botany

Background:

• Rapid plant speciation is linked to floral spur evolution and its impact on reproductive success.
• Impatiens capensis (jewelweed) flowers feature a variable long, curved spur for nectar production and storage.

Purpose of the Study:

• To investigate the variability of floral spur shape in Impatiens capensis populations.
• To correlate spur shape with components of female and male reproductive success.
• To explore factors limiting spur angle evolution, including pollinator and nectar robber interactions.

Main Methods:

• Documenting natural variation in spur shape within and among Impatiens capensis plants.
• Correlating spur shape (length and curvature) with reproductive success metrics (seed production, pollen removal).
• Observing pollinator (bee) visit length and nectar availability in relation to spur curvature.

Main Results:

• Spur shape variation is greater among plants than within individual plants.
• Weakly directional natural selection on spur shape was observed in one of two years.
• Increased spur curvature correlated with higher seed production and pollen removal.
• Bees visited highly curved spurs longer but left more nectar in straighter spurs.
• Nectar robbers preferred highly curved spurs, potentially limiting selection for this trait.

Conclusions:

• Floral spur shape in Impatiens capensis is variable and under selection related to reproductive success.
• Opposing selection pressures from pollinators and nectar robbers may maintain spur shape variation.
• Temporal variation in selection strength and genetic correlations could also influence spur evolution.