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A variação nos atributos florais está relacionada à polinização por engano em orquídeas?

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Author(s):
João Marcelo Robazzi Bignelli Valente Aguiar
Total Authors: 1
Document type: Doctoral Thesis
Press: Campinas, SP.
Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
Defense date:
Examining board members:
Marlies Sazima; Thibaud Aymeri Lancelot Monin; Isabel Alves dos Santos; Fábio Pinheiro; Michael Hrncir
Advisor: Marlies Sazima
Abstract

Deceptive pollination, a strategy common among orchids (Orchidaceae) occurs when flowers offer no reward to pollinators and draw them, nevertheless, by means of conspicuous and attractive signals, such as color and fragrance. Having variable attracting signals may improve the efficiency of deception by hindering the establishment of predictions about the absence of reward. This idea was developed by Heinrich (1975), who argued that the more dissimilar are the non-rewarding flowers of a given species, the longer it should take pollinators to learn avoiding that species. Signal variability would thus impair generalization between non-rewarding experiences. In this thesis, we tested this hypothesis by focusing on the interaction between a tropical orchid species (Ionopsis utricularioides) and its floral visitors. We designed a series of cognitive experiments to address the question of what do pollinators perceive and learn when they face variable floral signals. First, we focused on visual information and characterized the intraspecific flower color variation of the orchid. We then trained stingless bees Scaptotrigona aff. depilis (Meliponini) to visit a setup of artificial flowers that were manipulated in color and presence of sugar reward to simulate the deceptive polymorphic flowers. We found that color variability disrupted the learning process, thus resulting in an increase of the number of flowers visited until learning that all flowers lacked reward. We also focused on olfactory information and characterized the intraspecific variation of flower fragrance in the orchid. We used components of the flower odorant profile and performed olfactory conditioning experiments with the honey bee Apis mellifera, a model for the study of learning and memory. Taking advantage of the olfactory conditioning of the Proboscis Extension Response (PER), we studied if bees discriminate between floral fragrance isomers, which are common in the fragrance of many food deceptive orchids. We found that honey bees discriminate isomers under specific conditions but tend to generalize between them in most of the cases. Thus, in a pollination context, these odor signals could seldom be used as predictive cues for the presence or absence of food. We also studied if abundant components within a floral bouquet dominate minor components, a cognitive phenomenon called overshadowing. If this were the case, the more abundant odors within an orchid fragrance could be used as salient cues to be learned in association with reward or absence of reward. We found that the major component of the orchid fragrance, was overshadowed by minor components that vary between individual flowers. Overshadowing was maintained even when the concentration of the abundant component was increased relative to those of the other odorants in the mixture. Thus, bees cannot learn the predictive value of the most abundant component of the orchid fragrance, a fact that could help maintaining deceptive pollination. Taken together, our findings show that olfactory and visual variability in deceptive orchids contributes to deceptive pollination by impairing associative learning of the absence of reward. Moreover, they indicate that evaluating pollination from the perspective of pollinator cognition can lead us to a more complete understanding of insect-flower interactions, and to comprehensive analyses of complex problems in pollination studies (AU)

FAPESP's process: 15/05919-8 - Is floral trait polymorphism related to pollination in deceptive orchids?
Grantee:João Marcelo Robazzi Bignelli Valente Aguiar
Support Opportunities: Scholarships in Brazil - Doctorate