Upper petal lip colour polymorphism in Collinsia heterophylla (Plantaginaceae): genetic basis within a population and its use as a genetic marker

Abstract

Understanding the genetics of a polymorphic trait is important to predict its likely evolution. In Collinsia heterophylla, the upper petal lip colour can be either be white or white with a purple band, while the lower petal lip colour is invariably purple. Because the corolla is only partly polymorphic, the polymorphism can not have evolved due to a mutation where a pigment was lost in the entire plant, which is common in other polymorphic species. In a previous study, high frequency of the purple band was found in populations with darker flowers, indicating possible selection for this trait. In this study, I determined inheritance of the colour polymorphism using two populations (one with only white morph and other with both morphs). I conducted experimental crosses within and between floral morphs to determine whether patterns of segregation in offspring conform to single-gene predictions. Data from F1, F2, F3 and backcross progeny are consistent with a genetic model of one major locus with presence of the band being completely dominant, as indicated in earlier studies using distantly related populations. A novel finding in this study was that the two morphs did not show a difference in seed germination frequency or seedling survival. This trait can thus be valuable as a genetic marker. Even though more thorough ecological data are needed to understand the potential selection pressures on upper petal lip colour in C. heterophylla, its simple inheritance may indicate the possibility of fast evolutionary response to selective forces acting on this trait.

Selection on pollen and pistil traits during pollen competition is affected by both sexual conflict and mixed mating in a self‐compatible herb

“…Flowers have a zygomorphic corolla with two lips and are arranged in whorls on spikes. Corolla color varies from white to purple on the upper lip and from pale to dark purple on the lower lip; some populations, such as the one used in the present study, are dimorphic for presence/absence of a dark band on the upper lip (Lankinen, 2009). Flowers develop into capsules.…”

Arctic Mustard Flower Color Polymorphism Controlled by Petal-Specific Downregulation at the Threshold of the Anthocyanin Biosynthetic Pathway

“…Although the same alleles are expressed in petals and leaves, the significant CHS expression difference between purple- and white-flowered individuals is confined to petals, consistent with our phenotypic survey that identified no correlation between petal and vegetative pigmentation. Organ-specific changes in ABP gene expression are not uncommon and likely persist in natural populations since they prevent any deleterious pleiotropic effects of losing flavonoid intermediates and anthocyanin pigments in vegetative tissues [36], [42], [50], [51]. Petal-specific downregulation in the ABP would also prevent more subtle pleiotropic consequences recently associated with floral anthocyanin polymorphisms such as changes in floral scent [52] and decreased leaf glucosinolate induction [6].…”

Geographic variation in floral traits is associated with environmental and genetic differences among populations of the mixed mating species Collinsia heterophylla (Plantaginaceae)

“…Populations differ in the intensity of purple on the lower lip and some populations are polymorphic for presence/absence of dark pigment on the upper lip. In flowers with a dark upper lip, the pigment is often restricted to a distinct band, a trait determined by a single dominant gene (Weil and Allard 1964;Lankinen 2009). At flower opening, anthers are undehisced and the stigma is non-receptive.…”