Genetic variation in the honesty of plants to their pollinators

Abstract

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• Pollinators prefer flowers with traits that reliably indicate reward quality or quantity, a relationship defining ‘honest signals’. Despite its prevalence in plant–pollinator interactions, genetic variation in floral honesty and its effects on plant fitness remain poorly understood.
• Using a clonal design, we propagated 41 genotypes of Turnera velutina from a natural population to estimate broad-sense heritability and genetic variation in floral morphological traits, nectar, and floral honesty (i.e. the signal–reward correlation). In a factorial experiment, we exposed combinations of ‘less honest’ and ‘more honest’ genotypes with above- or below-average nectar sugar content to natural pollinators and recorded pollinator visitation patterns and plant fitness.
• We found significant heritability and genetic variation in floral traits and the signal–reward correlation, indicating that floral honesty has the potential to evolve through pollinator-mediated selection. Pollinators preferred honest plants with larger flowers and higher nectar sugar content, spending more time on them. These plants also produced more seeds per fruit than other genotypes.
• Our study addresses key knowledge gaps in the evolution of floral honesty by revealing its genetic basis and demonstrating that a positive signal–reward relationship can be shaped by natural selection through plant–pollinator interactions.