International Union for the Study of Social Insects (IUSSI2018), August 5-10, 2018 in Guarujá, Brazil.

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A pollinators’ report on odorant dominance in deceptive orchid’s fragrances

Author(s):
João Marcelo Robazzi Bignelli Valente Aguiar, João Marcelo Robazzi Bignelli Valente Aguiar , Ana Carolina Roselino , Marlies Sazima , Martin Giurfa
Institution(s):
Centre de Recherches sur la Cognition Animale, Université Paul Sabatier – Toulouse III, Toulouse, France; Instituto de Biologia, Universidade Estadual de Campinas, Campinas, Brasil; Centre de Recherches sur la Cognition Animale, Université Paul Sabatier – Toulouse III, Toulouse, France; Instituto de Biologia, Universidade Estadual de Campinas, Campinas, Brasil ; Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brasil ; Instituto de Biologia, Universidade Estadual de Campinas, Campinas, Brasil ; Centre de Recherches sur la Cognition Animale, Université Paul Sabatier – Toulouse III, Toulouse, France
Bees forage for food in flowers and learn to associate different floral cues, such as color and fragrance, with the presence of reward. Yet, some flower species do not offer food rewards and still attract pollinators using deceptive strategies, as some highly polymorphic orchids. It has been suggested that this polymorphism promotes more visits to deceptive flowers by disrupting the learning process of the pollinators. We tested this hypothesis by focusing on the case of the deceptive orchid Ionopsis utricularioides. We studied the learning and generalization capabilities of honey bees trained with odor signals derived from this orchid’s variable fragrance. We chose four odorants from the floral bouquet of the species: the major component β-ocimene and three minor components, decanal, β-myrcene and phenylacetaldehyde. We asked if the major component dominates in an odor mixture including a minor component, as expected from olfactory learning experiments . This phenomenon, termed overshadowing, would be prejudicial for deceptive-orchid pollination as an odor cue could be learned as reliable predictor of the absence of reward. We used the olfactory conditioning of the Proboscis Extension Response (PER), which allows training a bee to associate an odor or a binary odor mixture with sucrose reward. After being trained to a binary mixture of ocimene and a minor odor component, bees responded always more to the minor component than to ocimene in the test. In this case, their response to ocimene was smaller than that recorded after training ocimene alone. Thus, despite its abundance in I. utricularioides bouquet, ocimene was overshadowed by the minor components, even when its concentration was increased with respect to the other odorant in the mixture. This would impede the learning of a reliable cue as predictor of the absence of reward and leave pollinators with variable odor cues, which could disrupt avoidance learning of the orchid.
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