Flower color polymorphism and speciationLysimachia monelli and Lysimachia arvensis as study systems

Resumen

Flower color, along with other floral traits, is a character linked to the reproductive success, since it participates in pollinator attraction. Different selective pressures act on this trait, from biotic factors such as pollinators, to abiotic factors such as environmental stress, promoting speciation. The great diversity of flower colors in nature is mainly due to the presence of pigments. Anthocyanins are the predominant pigments in flowers and are synthesized in the anthocyanin biosynthetic pathway (ABP). Variations in the structural and regulatory genes that participate in this pathway are key to redirect the flux towards the synthesis of different types of anthocyanins. In nature there are species with floral color polymorphism, that is, they have more than two different morphotypes. Since each morphotype could have different selective pressures, polymorphisms are a source of speciation. Then, species with floral color polymorphism are good systems to study the role of flower color in speciation processes. In this PhD dissertation, we address the study of flower color polymorphism shared by two closely related species, Lysimachia monelli and Lysimachia arvensis, with blue and orange flowers colors, from a multiscale perspective. We deepen into the repercussion that polymorphism has on the reproductive isolation and biogeography of L. monelli (aspects already studied previously in L. arvensis), and we explore the main pigments and the genes involved in their synthesis in both species through the analysis of the petals’ transcriptome. The results show that the color lineages of both species are in an advanced stage of speciation. Specifically, L. monelli presents a total geographic isolation, and under a possible secondary contact between both colored lineages, only the postzygotic barriers would suppose an important isolation between them (38%). Although there is evidence of gene flow in the past, the lineages of L. monelli currently present different niches, marked by different climatic and edaphic characteristics. Both lineages have the same groups of pollinators, which are capable of visually distinguishing both colors, so abiotic factors play an important role in maintaining color polymorphism in L. monelli. On the other hand, we found the same key genetic and biochemical bases for color variation in both species, suggesting a single blue-to-orange transition event in these Lysimachia species. Finally, we discuss the possible origin of the color polymorphism, since the phylogenetic analyzes of several genes involved in floral color contrast with the results obtained in a recent study based on ITS markers. This doctoral thesis shed light into the molecular bases of floral color variations in L. arvensis and L. monelli. In addition, it shows the current status of reproductive isolation and the biogeography of the floral color lineages of L. monelli.