Floral biology of hybrid zones

Abstract

Abstract Hybridization between closely related species is relatively common in angiosperms and can create a natural hybrid zone. We review recent experimental studies of floral biology in pairs of hybridizing species, emphasizing comparisons of the floral morphology and nectar rewards of hybrid plants with that of their progenitors, and quantifying the influence of these floral traits on pollinator behaviour and prezygotic and post-zygotic reproductive isolation. Floral traits of hybrids can be intermediate or transgressive. Floral differences between species, which in one case are attributable to particular chromosomal regions, can have differing impacts on interspecific flights by pollinators. A simulation model of mating in a hybrid zone between ıpomopsis aggregata and ıpomopsis tenuituba shows that behavioural responses by hummingbird and hawk-moth pollinators affect pre-zygotic ethological isolation more strongly than mechanical isolation.