How did bilaterally symmetric flowers evolve from radially symmetric ones? To address this important question, geneticists Francisco Perfectti and Juan Pedro M. Camacho, and ecologist Jos M. Gmez (Universidad de Granada, Spain) explored how different flower shapes affected plant fitness in natural populations of Erysimum mediohispanicum, a Mediterranean herb. Their findings will be published in the October issue of The American Naturalist.

The researchers found that plants bearing bilaterally symmetrical flowers were more visited by pollinators and had higher fitness, measured by both the number of seeds produced per plant and the number of seeds surviving to the juvenile stage, than plants with radially symmetric flowers.

"This study reveals that natural selection can play a key role in the evolution of flower bilateral symmetry," says Camacho. "Our data also suggest that it is possible to understand the evolution of complex forms by means of microevolutionary analyses, as complementary tools to those coming from developmental genetics."