Tansley insight Pleiotropy and theevolutionof floral integration

Floral traits often show correlated variation, bothwithin and across species. One explanation for this pattern of floral integration is that different elements of floral phenotypes are controlled by the samegenes, that is, that thegenetic architecture is pleiotropic. Recent studies froma rangeof model systems suggest that the pleiotropy is common among the loci responsible for floral divergence.Moreover, theeffects of allelic substitutions at these loci areoverwhelmingly aligned with direction of divergence, suggesting that the nature of the pleiotropic effects was adaptive. Molecular genetic studies have revealed the functional basis for some of these effects, although much remains to be discovered with respect to the molecular, biochemical and developmental mechanisms underlying most quantitative trait loci (QTL) responsible for floral differences. Developing adetailed understandingof the nature of pleiotropicmutations and their phenotypic consequences is crucial formodelinghow thegenetic architectureof trait variation influences the tempo and trajectory of floral evolution.