Understanding the origin of species is one of the major challenges of modern biology, and requires the integration of ecological, evolutionary and developmental approaches. In this project, we aim to understand speciation processes in plants using a clade of eight Iberian bifid toadflaxes (Linaria sect. Versicolores) as a model system, and applying a multidisciplinary approach. Particular attention will be paid to investigating the role of evolutionary variation in the length of nectar spurs in mediating speciation, as nectar spurs have been previously hypothesized as a key innovation promoting speciation in angiosperms.Particular objectives are as follows:(1) To reconstruct phylogenetic relationships within the study clade using multiple unlinked DNA regions and state-of-the-art coalescent-based methods. Based on phylogenetic results, ancestral states of key traits (particularly spur length) involved in species differentiation will be reconstructed.(2) To investigate the components of reproductive isolation among species of the study clade, including prezygotic (pollinators, environmental niche) and postzygotic breeding barriers.(3) To understand the genetic and developmental basis of a key flower trait, spur length, putatively involved in speciation of the study clade. To this end, we will build upon previous work on flower development in the tribe Antirrhineae and genus Linaria. First, we will analyze the transcriptional basis of spur development in Linaria using next-generation sequencing technology. Then, inter-specific differences in expression patterns of genes potentially involved in regulating spur length variation will be examined.In the end, information on phylogenetic relationships, reproductive barriers, evolution and development of key traits will be integrated in order to understand mechanisms of speciation in Linaria sect. Versicolores.