Variation in the strength of association among pollination systems and floral traits: Evolutionary changes in the floral traits of Bornean gingers (Zingiberaceae)

Premise of the study: Diversification of floral traits in angiosperms is often attributed to have been driven by adaptations to pollinators. Nevertheless, phylogenetic studies on the relationships among evolutionary changes in floral traits and pollination systems are still limited. We examined the relationships between floral trait changes and pollinator shifts in Bornean gingers (Zingiberaceae). These plants have strongly zygomorphic flowers pollinated by spiderhunter birds, bees of the genus Amegilla, and halictid bees.

Methods: We identified pollination systems through field observations and recorded petal color, quantity of floral rewards, and seven measures of flower morphology in 28 ginger species. Phylogenetic trees were constructed from nucleotide sequences of the matK and ITS regions. We examined the correlations between the evolution of pollination systems and floral traits using phylogenetically independent contrasts.

Key Results: Significant association was found between pink color and spiderhunter pollination, orange and Amegilla pollination, and yellow and white and halictid pollination. Sugar production was higher in spiderhunter-pollinated species and lower in halictid-pollinated. Meanwhile, there was a significant association only for a subset of the floral morphological characters measured. Floral tube length, which is often thought to evolve to match the lengths of pollinator probing apparatuses, did not show any correlation.

Conclusions: There is considerable variation in the strength of association among pollination systems and floral traits. Lack of significant correlation in some traits could partly be explained by floral functions other than pollination, such as adaptations to prevent herbivore damage to the ovules. Further studies on these factors may improve understanding of plant–pollinator interactions.