ECOLOGY/EVOLUTION

Symmetry and Speciation

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Science  20 Feb 2004:
Vol. 303, Issue 5661, pp. 1106
DOI: 10.1126/science.303.5661.1106d

Evolutionary theory predicts that there will be higher potential for diversification in groups of organisms that have traits that promote reproductive isolation between populations. For plants, one such feature is floral symmetry. Bilaterally symmetrical (zygomorphic) flowers such as orchids allow for more precise collection and placement of pollen by visiting animal pollinators than do radially symmetrical (actinomorphic) flowers such as buttercups. Mutations that cause changes in the shape and dimensions of zygomorphic flowers have the potential to generate reproductive isolation between populations by decreasing pollinator-mediated gene flow.

Sargent compared species richness between zygomorphic and actinomorphic lineages in related animal-pollinated groups of plants. The zygomorphic lineages, in 15 out of 19 cases, were more species-rich than the actinomorphic lineages. Assuming that extinction rates are not higher in the actinomorphic lineages, this suggests that animal pollination indeed promotes the likelihood of reproductive isolation and speciation in plants with bilaterally symmetrical flowers. — AMS

Proc. R. Soc. London Ser. B 10.1098/rspb.2003.2644 (2004).

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