Functional Significance of Labellum Pattern Variation in a Sexually Deceptive Orchid (Ophrys heldreichii): Evidence of Individual Signature Learning Effects

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.

Fluctuating selection across years and phenotypic variation in food-deceptive orchids

“…Factors maintaining high levels of phenotypic variation in deceptive systems have been investigated in several studies (see Juillet & Scopece, 2010 and references therein), particularly after Heinrich ’s (1975) proposal that phenotypic variability decreases pollinator avoidance learning, thereby increasing orchid reproductive success. This hypothesis has also been recently suggested by Stejskal et al (2015) to explain variation in the labellum patterns of a sexually-deceptive orchid. However, Juillet & Scopece (2010) showed that all attempts to identify a reproductive advantage linked with phenotypic variation in food-deceptive species were non-significant or indicated a lower reproductive success thus underlining the need of more studies to support or discard this hypothesis.…”

Recognition of human face images by the free flying wasp Vespula vulgaris

“…The wasp was then allowed to approach the apparatus again to make a novel choice. This method was developed to promote learning of complex patterns including faces in free flying honeybees (Avarguès-Weber, Portelli, et al, 2010;Dyer et al, 2005Dyer & Vuong, 2008;Stejskal et al, 2015). This procedure avoided positional learning of the rewarding stimuli and ensured that the stimuli could be visually inspected between choices.…”

“…The impressive visual learning abilities by honeybees could be explained by the fact that these pollinators often rely on the complex visual signals of flowers to acquire food. For example, bees may need to memorize complex flower patterns to avoid deceptive plant flowers (Stejskal, Streinzer, Dyer, Paulus, & Spaethe, 2015). Interestingly, it has also been demonstrated that honeybees have the capacity to rely on configural processing with prolonged visual experience (Avarguès-Weber, Portelli, et al, 2010;Stach, Benard, & Giurfa, 2004;Stach & Giurfa, 2005), thus offering a fascinating parallel with primate visual processing (Avarguès-Weber et al, 2015).…”

Does size really matter? A comparative study on floral traits in orchids with two different pollination strategies

“…; Stejskal et al . ), we hypothesised that trait variance might differ between the two strategies. Generally, variation in sterile traits was found to be larger than variation of the fertile portions.…”