Abstract
Homeotic changes played a considerable role during the evolution of flowers, but how floral homeotic mutants initially survive in nature has remained enigmatic. To better understand the evolutionary potential of floral homeotic mutants, we established as a model system Stamenoid petals (Spe), a natural variant of Capsella bursa-pastoris (Brassicaceae). In the flowers of Spe plants, petals are transformed into stamens, whereas all other floral organs are unaffected. In contrast with most other homeotic mutants, the Spe variant occurs in relatively stable populations in the wild. In order to determine how the profound change in floral architecture influences plant performance in the wild, we performed common garden experiments running over 3 years. Here, we show that Spe and wild-type plants attract the same assemblage of floral visitors: mainly hoverflies, wild bees and thrips. However, floral visitation is about twice as frequent in wild-type plants as in Spe plants. Nevertheless, the numbers of seeds per fruit were about the same in both variants. Wild-type plants produced more flowers, fruits and seeds per plant than Spe plants, whereas the germination capacity of Spe seeds was higher than that of the wild-type. Determination of volatile composition revealed monoterpenes and 3,4-dimethylbenzaldehyde, which were detected only in wild-type flowers, presumably because they are produced only by petals. Our data indicate that the similar fitness of Spe and wild-type C. bursa-pastoris in the field results from complex compensation between plant architecture and germination capacity. In contrast, flower structure and floral visitation are only of minor importance, possibly because C. bursa-pastoris is mainly self-pollinating.
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Acknowledgments
We gratefully acknowledge E. Stolle and F. Burger (Institute of Zoology, Halle) for taxonomic determination of Syrphidae and bees plus wasps, respectively. We also thank the undergraduate students Stefan Lukas, Christine Steinbach, Katja Kühdorf, Ulrike Schure and Sophie Bartsch for help in observations of the plots, and Jeanette Keim and Ulrike Schure for counting fruits and seeds. Many thanks also to Richard Bateman, David Roberts and an anonymous reviewer for valuable comments and suggestions that helped considerably to improve a previous version of this manuscript. We are especially grateful to Richard Bateman for his continuous encouragement to work on this topic. This project was supported by grants from the Deutsche Forschungsgemeinschaft (TH 417/4-1 and -2 to G.T., NE 314/7-1 and -2 to B.N.).
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Ziermann, J., Ritz, M.S., Hameister, S. et al. Floral visitation and reproductive traits of Stamenoid petals, a naturally occurring floral homeotic variant of Capsella bursa-pastoris (Brassicaceae). Planta 230, 1239–1249 (2009). https://doi.org/10.1007/s00425-009-1018-z
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DOI: https://doi.org/10.1007/s00425-009-1018-z