Floral adaptation and modular trait evolution associated with a shift from bee to hummingbird pollination

Area of Science:

• Evolutionary Biology
• Plant Sciences
• Ecology

Background:

• Pollination shifts can lead to floral divergence, but their impact on trait variation and correlation remains largely unknown.
• Understanding these shifts is crucial for comprehending plant adaptation and speciation processes.

Purpose of the Study:

• To investigate how a transition from bee to hummingbird pollination influences floral phenotypic variation, functional integration, and morphological modularity in Neotropical spiral gingers (Costus kuntzei and Costus wilsonii).
• To assess pollinator assemblages and pollination syndrome divergence between sister species with different pollination strategies.

Main Methods:

• Field measurements and observations of pollinator assemblages and floral traits (shape, size, color, scent, nectar).
• Quantification of floral phenotypic variation and integration.
• Geometric morphometric analyses to evaluate modularity hypotheses based on floral function and developmental constraints.

Main Results:

• Costus wilsonii, pollinated by hummingbirds, showed trait loss and specialization on hermit hummingbirds, while Costus kuntzei, bee-pollinated, had a more diverse pollinator assemblage.
• Both species exhibited similar patterns of floral variation, integration, and modularity.
• Reduced variation and modularity were concentrated in traits critical for pollinator fit and pollen transfer.

Conclusions:

• Phenotypic patterns in floral traits are shaped by divergent pollinator-mediated adaptation.
• The shift in pollination strategy has resulted in stable trait variation and correlation patterns, indicating selection for efficient pollination and pollinator fit in both species.