Within-species floral evolution reveals convergence in adaptive walks during incipient pollinator shift

Area of Science:

• Evolutionary biology
• Plant speciation
• Molecular evolution

Background:

• Adaptive walks link phenotypes, genes, and fitness, driving evolutionary change.
• Floral evolution, particularly color shifts, can lead to rapid reproductive isolation and speciation.
• Monkeyflowers (Mimulus sect. Erythranthe) exhibit convergent evolution of yellow flowers from red ancestors, suggesting pollinator shifts.

Purpose of the Study:

• To investigate convergent evolution in yellow-flowered monkeyflower morphs (M. cardinalis and M. verbenaceus) compared to their red-flowered relatives.
• To analyze floral phenotypes, biochemistry, transcriptomics, genomics, and pollinator interactions in these morphs.
• To elucidate early stages of adaptive walks and their role in reproductive isolation and speciation.

Main Methods:

• Comparative analysis of floral traits, pigment biochemistry, and gene expression.
• Transcriptomic and genomic variation assessment.
• Pollinator interaction observations and preference tests.

Main Results:

• Both yellow morphs show convergent evolution in large-effect traits like floral pigments and gene expression.
• Yellow flowers are strongly preferred by bumblebees over hummingbirds.
• Smaller-effect changes in scent and floral size also favor bee pollination, indicating shifts from hummingbird pollination.

Conclusions:

• Convergent large-effect mutations (floral color) can drive pollinator attraction and initiate adaptive walks.
• Subsequent smaller-effect changes facilitate adaptation to new pollinators.
• These ongoing adaptive walks contribute to reproductive isolation and incipient speciation through convergent evolution.