Journal Article

Evolutionary Trends in the Flowers of Asteridae: Is Polyandry an Alternative to Zygomorphy?

Florian Jabbour, Catherine Damerval and Sophie Nadot

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 102, issue 2, pages 153-165
Published in print August 2008 | ISSN: 0305-7364
Published online May 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcn082
Evolutionary Trends in the Flowers of Asteridae: Is Polyandry an Alternative to Zygomorphy?

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  • Ecology and Conservation
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Background and Aims

Floral symmetry presents two main states in angiosperms, actinomorphy (polysymmetry or radial symmetry) and zygomorphy (monosymmetry or bilateral symmetry). Transitions from actinomorphy to zygomorphy have occurred repeatedly among flowering plants, possibly in coadaptation with specialized pollinators. In this paper, the rules controlling the evolution of floral symmetry were investigated to determine in which architectural context zygomorphy can evolve.

Methods

Floral traits potentially associated with perianth symmetry shifts in Asteridae, one of the major clades of the core eudicots, were selected: namely the perianth merism, the presence and number of spurs, and the androecium organ number. The evolution of these characters was optimized on a composite tree. Correlations between symmetry and the other morphological traits were then examined using a phylogenetic comparative method.

Key Results

The analyses reveal that the evolution of floral symmetry in Asteridae is conditioned by both androecium organ number and perianth merism and that zygomorphy is a prerequisite to the emergence of spurs.

Conclusions

The statistically significant correlation between perianth zygomorphy and oligandry suggests that the evolution of floral symmetry could be canalized by developmental or spatial constraint. Interestingly, the evolution of polyandry in an actinomorphic context appears as an alternative evolutionary pathway to zygomorphy in Asteridae. These results may be interpreted either in terms of plant–pollinator adaptation or in terms of developmental or physical constraints. The results are discussed in relation to current knowledge about the molecular bases underlying floral symmetry.

Keywords: Floral symmetry; architectural constraints; Asteridae; comparative analysis; composite tree; correlated evolution; evolutionary scenario

Journal Article.  8175 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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