Abstracts (first author)
Pollinator-restrictive flower traits determine evolutionary optima with differential diversification rates in bifid toadflaxes (Linaria sect. Versicolores)
The role of flower specialization in plant speciation and evolution remains controversial. Here we analyzed the evolution of flower traits restricting the access to pollinators in the bifid toadflaxes (Linaria sect. Versicolores), a monophyletic group of c. 30 species and subspecies with highly specialized corollas. A time-calibrated phylogeny based on both nuclear and plastid DNA sequences was obtained using a coalescent-based method, and flower morphology was characterized by means of morphometric analyses. Using recently-developed methods, directional trends in morphological traits and trait-dependent diversification rates were jointly analyzed, and morphological shifts were reconstructed along the phylogeny. Our results indicated that a restrictive character state (narrow corolla tube) may be ancestral to Linaria sect. Versicolores. After its early loss in the most species-rich clade, this character state has been convergently reacquired in multiple lineages of this clade in recent times, yet it has exerted a negative influence on diversification rates. Comparative analyses and pollinator surveys suggest that the narrow- and broad-tubed flowers are evolutionary optima representing divergent strategies of pollen placement on nectar-feeding insects. We therefore suggest that opposing individual-level and species-level selection pressures may have driven the evolution of pollinator-restrictive traits in bifid toadflaxes.