Bird-pollinated Macaronesian Lotus (Leguminosae) evolved within a group of entomophilous ancestors with post-anthesis flower color change

We analyzed the evolution of red/orange flowers in four putatively bird-pollinated species of Macaronesian Lotus, with the aim of investigating whether this floral trait evolved from a similar trait found in some entomophilous Lotus species, namely the ability to modify flower color to red after anthesis. First, we mapped the ability to modify flower color in this group on a well-resolved and densely sampled phylogenetic tree of the Macaronesian Lotus. Secondly, we determined differences in light reflectance and pigment composition between petals of (1) prechange and postchange flowers in bee-pollinated species and (2) between bee and putatively bird-pollinated species. Post-anthesis flower color change evolved three times within Macaronesian Lotus, and putatively bird-pollinated species evolved within a clade with this ability to change flower color to red after anthesis. The evolutionary transition to red/orange flowers in the putatively bird-pollinated species involved biochemical changes similar to those of the developmental transition to red postchange flowers. In both cases there are changes in the composition of flavonols and anthocyanidins within the same metabolic pathways, especially in the cyanidin branch of pigment production, but not the activation or inactivation of additional branches of this pathway. Post-anthesis color change in Lotus, from yellow to red, is thought to be an adaptation to reduce bee visits to already pollinated flowers. Our results are consistent with the hypothesis that constitutive red coloration for bird-pollination evolved from facultative red flower color change in Lotus. As red post-anthesis coloration is widespread in plants, this may possibly represent a widespread exaptive mechanism for the evolution of bird pollination.