Increased reliance on diurnal pollination in a geographically and morphologically atypical sand verbena

Abstract

Premise—Pollinator-mediated selection drives floral morphologies to converge on sets of traits deemed “pollination syndromes”. As a result of similarity due to common descent, pollination syndromes can be shared among closely related plants in cases where pollinators remain relatively constant over evolutionary time. In these cases, species that display trait deviations away from their ancestral states may indicate hidden pollinator shifts. Identifying when and where trait deviations reflect reproductive contributions from unexpected pollinators is important for understanding the boundaries and cohesion of pollination syndrome phenotypes. Methods—The floral morphology of heart’s delight, Abronia ameliae, unites a collection of traditional moth-pollination syndrome traits, typical for the genus, with several characters odd for moth pollination, including diurnally open, pink flowers and large, tall inflorescences. We predicted that the evolution of this combination of traits reflects a change in pollinators from other Abronia, specifically that this species is primarily diurnally-pollinated. We conducted pollinator-exclusion experiments in a natural population and a common garden to determine the independent reproductive contributions of diurnal and nocturnal pollinators to A. ameliae and characterized its volatile profile. Results—We found that A. ameliae is indeed primarily diurnally pollinated: visitation by day-active butterflies and moths contributed to higher seed set than visitation by nocturnal moths. However, A. ameliae also emits nocturnal moth-associated volatile compounds and receives considerable nocturnal pollination. Conclusions—We suggest that the unusual phenotypes found in A. ameliae flowers relative to the genus reflect a shift in reproductive contributions to incorporate mostly diurnal pollination and transition to a mixed pollination strategy that blends diurnal and nocturnal pollination phenotypes.

Keywords

• Abronia ameliae
• butterfly pollination
• floral trait evolution
• floral pigmentation
• moth pollination
• volatile organic compounds