Selfing Maintains Flower Colour Polymorphism In L. arvensis Despite High Inbreeding Depression

Flower colour polymorphism (FCP) is frequently associated with differences in pollinator attraction. FCP maintenance is intriguing, as positive directional selection by pollinators should result in the loss of polymorphism. Autonomous selfing could confer reproductive assurance when pollen is limited, and could be a mechanism for maintaining polymorphism unless inbreeding depression is high. We study the role of selfing in maintaining FCP in Lysimachia arvensis, a species with blue and red morphs co-occurring in Mediterranean populations, where pollinators negatively select for the red morph. We experimentally assessed inbreeding depression in both morphs in two Mediterranean populations and genetic diversity was studied via AFLP and SSR microsatellites in 20 populations. Between-morph genetic differentiation was high and the red morph had a lower genetic diversity, mainly in the Mediterranean. Results also show strong phenological differences between selfed and outcrossed progeny, and a high ID of the red morph. The low genetic diversity of the red morph is in concordance with a reproductive system based predominantly on selfing. However, ID suggests a limited capacity for red morph recruitment, according to its low frequency in polymorphic populations. Genetic differentiation between morphs indicates a low gene flow between them, opening the possibility of reproductive isolation and speciation in Lysimachia arvensis.