Floral signals of the dimorphic oil-producing Byrsonima sericea (Malpighiaceae): is the eglandular morph deceptive?

Abstract

Background: Presence of eglandular individuals (lacking floral oil glands) within populations of several neotropical Malpighiaceae is intriguing, with ecological and evolutionary implications so far unexplored. This floral dimorphism (glandular and eglandular individuals) is hypothesised to be related to energetic costs of oil production and pollinator deception. Aims: To evaluate whether eglandular individuals of Byrsonima sericea deceive oil-collecting bees and obtain higher reproductive success (fruit production) compared to glandular individuals. Methods: We monitored flower visitation and quantified and identified floral cues (visual and olfactory) associated with glandular and eglandular individuals, and measured fruit set. Results: Both morphotypes exhibited similar visual cues and proportions of visits by oil-collecting bees and similar fruit set. Floral scent via headspace analysis indicated no between-morphotype differences in biogenic volatile organic compounds, whilst flower extract samples showed a clear difference in chemical composition. Conclusions: Absence of oil production in B. sericea was not associated with changes in floral cues used in pollinator attraction at long distances. Maintenance of floral cues may be a deceptive mechanism that maintains the oil-collecting behaviour of bees on flowers that lack oil glands. Higher fruit set was not observed in eglandular individuals, suggesting that energetic costs associated with oil production do not involve fruit production.