Genetic variation in the honesty of plants to their pollinators

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.