Abstract
Mimicking female insects to attract male pollinators is an important strategy in sexually deceptive orchids of the genus Ophrys, and some species possess flowers with conspicuous labellum patterns. The function of the variation of the patterns remains unresolved, with suggestions that these enhance pollinator communication. We investigated the possible function of the labellum pattern in Ophrys heldreichii, an orchid species in which the conspicuous and complex labellum pattern contrasts with a dark background. The orchid is pollinated exclusively by males of the solitary bee, Eucera berlandi. Comparisons of labellum patterns revealed that patterns within inflorescences are more similar than those of other conspecific plants. Field observations showed that the males approach at a great speed and directly land on flowers, but after an unsuccessful copulation attempt, bees hover close and visually scan the labellum pattern for up to a minute. Learning experiments conducted with honeybees as an accessible model of bee vision demonstrated that labellum patterns of different plants can be reliably learnt; in contrast, patterns of flowers from the same inflorescence could not be discriminated. These results support the hypothesis that variable labellum patterns in O. heldreichii are involved in flower-pollinator communication which would likely help these plants to avoid geitonogamy.
Highlights
Pollination by sexual deception is a rare and remarkable strategy in angiosperms as it constitutes an example of extreme floral specialization [1]
Labellum Pattern Variation in Ophrys heldreichii that almost all species of the Mediterranean orchid genus Ophrys, which comprises more than 250 species, achieve pollination by exploiting the mate-seeking behavior of insect males [5,6,7,8]
In the present study we tested whether the variation in bright and complex patterns on the labellum of O. heldreichii flowers can act as a visual cue that could promote learning by a pollinator after pseudocopulation, and be potentially beneficial for both the pollinator and the plant
Summary
Pollination by sexual deception is a rare and remarkable strategy in angiosperms as it constitutes an example of extreme floral specialization [1]. Whilst on a global basis, sexual deception is a rare strategy for plant pollination, it is interesting. Labellum Pattern Variation in Ophrys heldreichii that almost all species of the Mediterranean orchid genus Ophrys, which comprises more than 250 species, achieve pollination by exploiting the mate-seeking behavior of insect males [5,6,7,8]. During a subsequent visit by a male insect to another conspecific flower, the pollinia can come into contact with the stigma, facilitating pollination [4,7,9,10,11,12,13,14,15]. As the mating attempts are unsatisfactory for the bee, the male’s interest to visit other flowers usually decreases after a few minutes [6,13,14,16,17,18]
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