Flower colour segregation and flower discrimination under the bee vision model in the polymorphic Lysimachia arvensis

Floral colour determines pollinator behaviour, strongly affecting plant-mating systems. Lysimachia arvensis has blue- and red-flowered plants and colour inheritance remains largely unknown. A control of floral colour based on one locus, with the red allele as dominant, has been proposed. This proposal cannot explain the sporadic appearance of other floral colours in wild populations. We studied floral colour segregation in L. arvensis and assessed the possibility that pollinators can visually distinguish colour morphs by using Chittka's hexagon model, sigmoidal model of bee discrimination and experimental studies on pollinator attendance for two years. Hand crossing between morphs originated a homogeneous F1 with salmon-coloured flowers. In the F2, blue, red, salmon morphs and other plants with intermediate colours appeared, suggesting that more than one single locus are involved in colour segregation. Results from the sigmoidal discrimination model suggest that blue, red and salmon flowers can be discriminated by pollinators. In fact, pollinators showed strong colour constancy and discriminated against the salmon morph. Our study shows that Flower colour is a natural marker to assess the rate of crossing between morphs. The extreme rarity of salmon flowers in wild populations and flower constancy of L. arvensis pollinators indicates assortative mating.