Heat drastically alters floral color and pigment composition without affecting flower conspicuousness

Floral pigments primarily serve to attract pollinators through color display and also contribute to protection against environmental stress. Although pigment composition can be plastically altered under stress, its impact on pollinator color perception remains poorly understood. Moricandia arvensis (Brassicaceae) exhibits seasonal floral dimorphism, with lilac spring flowers and white summer flowers. This study examines how heat-driven shifts in floral pigments alter flower color and its perception by pollinators.

We conducted a comparative analysis of spring and summer floral morphs in a natural population by measuring petal spectral reflectance, analyzing absorption spectra of petal extracts, and modeling floral color in the visual systems of major pollinator functional groups. Additionally, UHPLC-ESI-MS/MS analysis was conducted under controlled conditions to characterize differences in phenolic profiles.

Spring flowers exhibited strong UV reflectance and a reduction in reflectance in the green spectrum, whereas summer flowers showed no UV reflectance and high reflectance in the visible range. Anthocyanins were detected only in spring flowers, while summer flowers accumulated high levels of UV-absorbing flavonoids. Despite these differences, both floral morphs remained visually conspicuous to hymenopterans, dipterans, lepidopterans, and coleopterans. Summer flowers produced twice as many phenolic compounds and accumulated higher concentrations, with ferulic acid and kaempferol derivatives the most prominent.

White summer flowers of Moricandia arvensis are not merely anthocyanin-deficient but exhibit a distinct profile of UV-absorbing phenolics that may confer heat tolerance while preserving floral conspicuousness to pollinators. These findings highlight the role of multifunctional traits in the evolution of flower color.