title: Intraspecific divergence and convergence of floral tube length in specialized pollination interactions.
abstract: Floral tubes are often thought to be a consequence of adaptive specialization towards pollinator morphology. We explore floral tube length evolution within Tritoniopsis revoluta (Iridaceae), a species with considerable geographical tube length variation. We ask whether tube lengths of T. revoluta populations are associated with pollinator proboscis lengths, whether floral divergence occurs in the presence of different pollinators and whether floral convergence occurs between distantly related populations pollinated by the same pollinator. Finally, we ask whether tube length evolution is directional. Shifts between morphologically different pollinators were always associated with shifts in floral morphology, even when populations were very closely related. Distantly related populations had similar tube lengths when they were pollinated by the same pollinator. Shifts in tube length tended to be from short to long, although reversals were not infrequent. After correcting for the population-level phylogeny, there was a strong positive, linear relationship between floral tube length and pollinator proboscis length, suggesting that plants are functionally specialized on different pollinators at different sites. However, because tube length evolution in this system can be a bidirectional process, specialization to the local pollinator fauna is unlikely to result in evolutionary or ecological dead-ends such as canalization or range limitation.
authors.affiliation: Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
authors.forename: B
authors.initials: B
authors.lastname: Anderson
authors.affiliation: Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
authors.forename: P
authors.initials: P
authors.lastname: Ros
authors.affiliation: Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
authors.forename: T J
authors.initials: TJ
authors.lastname: Wiese
authors.affiliation: Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa agellis@sun.ac.za.
authors.forename: A G
authors.initials: AG
authors.lastname: Ellis
mesh_terms: D000818:Animals; D001516:Bees / Q000033:anatomy & histology* / Q000502:physiology; D005075:Biological Evolution; D004175:Diptera / Q000033:anatomy & histology* / Q000502:physiology; D035264:Flowers / Q000033:anatomy & histology; D027621:Iridaceae / Q000033:anatomy & histology* / Q000502:physiology*; D010802:Phylogeny; D054817:Pollination; D013019:South Africa
keywords: cape flora; directional evolution; pollinator ecotype; pollinator specialization; trait matching