The selfing syndrome: a model for studying the genetic and evolutionary basis of morphological adaptation in plants

Abstract

Background: In angiosperm evolution, autogamously selfing lineages have been derived from outbreeding ancestors multiple times, and this transition is regarded as one of the most common evolutionary tendencies in flowering plants. In most cases, it is accompanied by a characteristic set of morphological and functional changes to the flowers, together termed the selfing syndrome. Two major areas that have changed during evolution of the selfing syndrome are sex allocation to male vs. female function and flower morphology, in particular flower (mainly petal) size and the distance between anthers and stigma.

Scope: A rich body of theoretical, taxonomic, ecological and genetic studies have addressed the evolutionary modification of these two trait complexes during or after the transition to selfing. Here, we review our current knowledge about the genetics and evolution of the selfing syndrome.

Conclusions: We argue that because of its frequent parallel evolution, the selfing syndrome represents an ideal model for addressing basic questions about morphological evolution and adaptation in flowering plants, but that realizing this potential will require the molecular identification of more of the causal genes underlying relevant trait variation.

Fig. 1.

Comparison of flowers from outbreeding and selfing species in the genus Capsella. Lateral views of flowers from the outbreeding C. grandiflora (left) and the autogamously selfing C. rubella (right). Note the reduced size of the petals, the reduced opening of the flower and the resulting smaller distance between stigma (arrow) and anthers in the flower of the selfer. See text for more details. Scale bar is 3 mm.