All flowers can be classified into two shapes: those with radial symmetry, like the lily, and those, like the orchid, with bilateral symmetry. The first flowers had radial symmetry, but the more complex bilateral form has evolved in many species, suggesting that it is favored by natural selection.
A team led by José Gómez of the University of Granada in Spain tried to find out why by studying 300 plants of the herb Erysimum mediohispanicum, which has the very rare trait of producing flowers with either radial or bilateral symmetry. The team measured the three-dimensional shape of each flower using a technique called geometric morphometry, relying on 32 landmarks on petals and corolla. From thousands of observations, they determined that most visits by pollinators were made by a small beetle. Statistical analysis revealed that the flowers with bilateral symmetry were more popular with the beetles. The bilaterals were also more fit, producing more seeds and progeny over the 2-year study, the team reports in The American Naturalist this month.
Two forms of Erysimum mediohispanicum.
CREDIT: JÓSE GÓMEZ ET AL. |
Risa Sargent, a plant evolutionary ecologist at the University of California, Berkeley, says Gómez and his team "make a strong case for a link between plant fitness" and bilateral symmetry. Next job: Find out the mechanism. The team speculates that the bilateral flowers offer a better "landing platform" for pollinators.
