Petunia as a Model System for the Genetics and Evolution of Pollination Syndromes

In recent years Petunia has become a promising model system for studying the genetics and evolution of pollination syndromes. Here we provide a brief introduction to the issue of pollination syndromes, explain why Petunia is a suitable model for its study, present useful background information about pollinators and plants, review recent studies, and discuss questions related to the genetics and evolution of Petunia pollination syndromes. 2.1 Petunia as a Model for the Evolution of Pollination Syndromes Flowering plants often feature pollination syndromes, sets of traits such as flower color, morphology, scent and nectar production, which appear to fit the morphology and behavior of specific pollinator types (Faegri and van der Pijl 1979). The general correspondence of floral traits and pollinators makes it possible to predict which pollinators are attracted to a given flower phenotype. The genus Petunia features three pollination syndromes: bee, hawkmoth, and hummingbird pollination. The bee-pollinated Petunia species, such as Petunia integrifolia, feature purple flowers with a wide floral tube into which bees crawl in order to reach pollen and nectar. These bee-pollinated flowers produce little nectar and hardly any scent. The hawkmoth-pollinated Petunia axillaris flowers feature white corollas with narrow tubes, allowing only nectar feeders with long probosces to reach the abundant nectar. Characteristic for hawkmoth-pollinated flowers, P. axillaris flowers produce large amounts of odor after dusk. Petunia exserta flowers bear the hallmarks of hummingbird pollination: the flower corolla is red, the petal limbs reflexed, anthers and style exserted, and the flowers emit no detectable scent. Similar to hawkmoth-pollinated flowers, P. exserta flowers have a long tube carrying copious amounts of nectar. T. Gübitz (B) Institute of Plant Sciences, Universität Bern, Altenbergrain 21, CH3013 Bern, Switzerland e-mail: [email protected] T. Gerats, J. Strommer (eds.), Petunia, DOI 10.1007/978-0-387-84796-2 2, C © Springer Science+Business Media, LLC 2009 29