Understanding the evolvability of flowers: a grand perspective of floral shape modularity

Yannick Städler, Sara Manafzadeh, Jürg Schönenberger

The key characteristics of organismal organization that contribute to evolvability are those that minimize developmental constraints. The most fundamental of these organisational characteristics is modularity, the independence between different aspects of the phenotype such that individual characters are able to evolve with little or no associated, and possibly detrimental, effects on other characters. For animal-pollinated plants, the coordination of several organs within each flower is needed to perform the complex functions of attraction and orientation of pollinators, and donation and receipt of pollen. Because pollinators may select for multiple independent functions, the floral phenotype has been hypothesised to be highly modular. The two main hypotheses of flower modularity are: the attraction (petals) vs. reproduction (stamens and carpel) hypothesis and the attraction (showy part of petals and sepals) vs. efficiency (functional part of petals and functional part of reproductive organs) hypothesis. In order to test these hypotheses, we outlined a null -ontogenic- hypothesis (each organ class as a module), and carried out a comparative analysis of 3D shape data on an unprecedented dataset of ca. 1500 flowers, from seven independent groups representing all major flowering plant lineages. Our sampling represents the flowering plant's diversity of breeding systems (selfing vs. outcrossing), breeding strategy (floral monomorphism vs. floral polymorphism) and pollinators (wind, insects, and vertebrates). We carried out shape correlation tests with known pollinators and shifts between pollination syndromes. Our results overwhelmingly support the presence of efficiency modules and highlight the importance of breeding system, pollination syndromes, and floral specialization as determinants of flower modules. Modularity represents a fertile conceptual framework through which elements of the classical theory of the evolution of flower morphology (e.g. convergent trends towards synorganisation and canalisation) can be viewed, quantified, and tested, as such this study is just a beginning.

Department of Botany and Biodiversity Research
Publication date
Austrian Fields of Science 2012
106042 Systematic botany, 106008 Botany, 106012 Evolutionary research
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