Rodent pollination in the African lily Massonia depressa (Hyacinthaceae)

Field studies in the semiarid Succulent Karoo region of South Africa showed that flowers of Massonia depressa (Hyacinthaceae) are visited at night by at least four rodent species, including two gerbil species. Live-trapped rodents were found to carry Massonia pollen on their snouts; they also had large quantities of Massonia pollen in their feces as a result of grooming their fur. Visits by insects to the flowers were infrequent at one site and apparently absent at another site. Plants enclosed in large-mesh wire cages, which excluded rodents but not insects, set very few seeds relative to open controls. Our initial hypothesis of rodent-pollination in M. depressa was based on the striking similarity of its flowers to those of unrelated, rodent-pollinated Protea species. Convergent traits include dull-colored and very robust flowers situated at ground level, a strong yeasty odor, and secretion of copious amounts of sucrose-dominant nectar during the evening when rodents are active. Despite having a low sugar concentration (∼20%), the nectar of M. depressa is almost 400 times as viscous as an equivalent sugar solution. The jelly-like constituent in the nectar may discourage robbing by insects, while also facilitating lapping by rodents. Our findings illustrate the utility of floral syndromes for generating testable predictions about pollination systems.