In Perfect Symmetry

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Science  15 Sep 2006:
Vol. 313, Issue 5793, pp. 1543
DOI: 10.1126/science.313.5793.1543a

Bilaterally symmetric flowers have evolved from radially symmetric flowers in a range of plant families, and this transition is usually correlated with a switch from generalist to specialist pollinators. Although the developmental changes involved in the transition are relatively well understood at the molecular genetic level, the selective forces behind it are less clear. Gomez et al. monitored the pollination rates of Erysimum mediohispanicum, a herbaceous plant of the southern Spanish mountains, which shows intraspecific variation in flower shape and is pollinated by beetles, bees, and hoverflies. The more bilaterally symmetric flowers were favored by the most abundant pollinating insect, the generalist beetle Meligethes maurus, and these flowers also produced the highest number of offspring. The significant fitness differences between flowers of differing shape suggest the adaptive route by which bilateral symmetry can evolve, even if the pollinators are generalists like most beetles. — AMS

Am. Nat. 168, 10.1086/507048 (2006).

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