Reconstruction of speciation by modification of major-effect genes in Petunia.

Reproductive isolation within and between populations was conventionally thought to proceed gradually through many mutations of small phenotypic effect. Contrary to this view, recent theory predicts that large-effect mutations become plausible when populations are far from their phenotypic optimum. Changes in pollinator assemblages severely compromise the reproductive success of many angiosperms, creating conditions conducive to mutations of large phenotypic effects. Here, we explore the role of major-effect genes in the evolutionary shift from hawkmoth to bee pollination in Petunia. By modifying six genes in the ancestral hawkmoth-pollinated P. axillaris phenotype, we created a mimic of the bee-pollinated P. secreta flower that is indistinguishable from this naturally evolved species both in its visual appearance and in behavioral assays. This study uniquely identifies the complete set of genes explaining the shift between two species, providing rare and compelling evidence for speciation by large-effect mutations.