Ecological genetics of floral evolution

The diversity of floral forms in nature can be explained largely as adaptations to the diversity of biotic and abiotic selective agents with which different plant species interact. Ecological genetics is the study of the process of adaptation, and therefore is an ideal approach to understanding floral adaptations. Here I review work on selection and genetic variance and covariance of floral traits, as these are the principal determinants of adaptive evolution. Early work focused on simple floral polymorphisms, because they were amenable to study, but more recent work has used their simplicity to understand the genetic mechanisms underlying adaptation in unprecedented detail. Because most floral adaptations are not simple polymorphisms, I also review studies that have measured selection and the G matrix (additive genetic variances and covariances among traits) for quantitative floral traits. I present new results from my research group on highly correlated traits in wild radish flowers, showing how these traits can evolve independently despite the constraint caused by the genetic correlation. A study of the same traits across the Brassicaceae suggests that macroevolution may be guided by the G matrix, but that independent evolution of highly correlated traits can also occur during these longer periods. I close by reviewing some topics for future study that have been opened up by recent technical advances, and which have the potential to expand our understanding of the mechanisms of floral adaptation greatly.