Behavioral Responses To Multi-Modal Stimulation: The Organization Of The Foraging Instinct Of Manduca Sexta

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The main objective of this doctoral thesis is to understand the adult foraging behavior of the nocturnal hawkmoth Manduca sexta. Adult M. sexta feed from the floral nectar of certain plants, which benefit from the pollination services resulting from these feeding visits. This mutualism has resulted in co-adaptive processes which link flower phenotypes with animal foraging behavior. The distinctive attributes of flowers, such as colors and odors, can exert an attraction on certain animals, particularly the ones that mediate their pollination. Therefore, in order to understand the foraging behavior of Manduca I focus on how responses to typical floral features, such as visual display and fragrance, allow this insect to get a nectar meal. My approach is purely experimental; I use different laboratory set-ups while manipulating artificial flowers to study responses to olfactory, visual, and tactile stimulation with the hope of understanding the appetitive behaviors, innate releasing mechanisms and motor patterns that together constitute the feeding instinct of Manduca. Throughout this thesis I explore 1) the role of tactile stimulation during flower ?handling?, and describe a type of non-associative learning which allows moths to improve their probing motor skills; 2) foraging at the stages preceding flower handling (approach and probing) by spatially and temporally decoupling olfactory and visual stimuli, which led to new insights on how successive motor patterns are released by different stimuli configurations as moths search for flowers; 3) the scale-dependent, contextual use of respiratory CO2 emanated from Datura wrightii flowers, and how dimorphic behavior suggests that nectar foraging and oviposition instincts are seamlessly integrated; 4) the visual associative learning capabilities of Manduca, and 5) how deficient larval nutrition, affecting the visual system, has an impact on foraging behavior. Results show that the effect of relevant stimuli cannot be disentangled from the context and scale in which they act. In fact, ?context? appears to be the releasing factor of particular motor patterns, suggesting that the consideration of stimuli without context is misguided. Meanwhile, scale becomes significant only under the framework of a sequential, hierarchical organization of the behavioral mechanisms constituting the feeding instinct of Manduca sexta.

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Manduca Sexta


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dissertation or thesis

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