Collaborative Research: Discrimination of Complex Mixtures in Olfactory Signaling

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For most of the animals that inhabit our planet the sense of smell is critical for survival. Odors are used to find food, shelter, and mates, as well as to mark territories. Sex pheromones are signals used by many animals, including insects, for the purpose of mate location, and are in almost all cases mixtures of chemicals. The exact blend, ratio and concentration of volatile compounds provides for precise communication between individuals of the same species. Indeed, most smells are mixtures and thus understanding how they are detected and processed by the nervous system is of fundamental interest to research on olfaction in general. Many insects exhibit distinct differences in body form between juvenile and adult stages. The adult antenna (the insect 'nose') is formed during metamorphosis from a patch of tissue known as the antennal imaginal disc. Similar discs give rise to other adult-specific structures such as wings, legs, eyes and genitalia during metamorphosis. The three related moth species that will be used in this project all utilize different mixtures in their sex pheromones. Males of each species have a different set of sensory neurons on the antenna that detect the volatiles present in the unique pheromone mixture released by their females. During metamorphosis the antennal imaginal disc gives rise to all the sensory neurons that will populate the adult antenna. Processes from these neurons called axons grow into the developing brain where they interact with other central neurons to produce the antennal lobe. This structure is comparable to the human olfactory bulb and it is the site where initial processing of olfactory information occurs. Because the antennal imaginal disc is a discrete patch of tissue it can be removed from a caterpillar that is about to enter into the metamorphic stage and transplanted into a host caterpillar of a different species. After metamorphosis, individual male moths that have received a transplanted antenna can be flown in a wind tunnel to determine the odor mixtures that they prefer. Subsequently recordings can be made both from individual hairs that house olfactory sensory neurons on the antenna and central olfactory neurons that populate the antennal lobe. The combination of behavioral and neurophysiological approaches will provide generally applicable insights into the mechanisms that control the wiring of connections between neurons in the brain and how specifically this contributes to the ability of moths and other animals to process and discriminate amongst different odor mixtures. The partnership between investigators at Cornell University and the University of Utah will involve the continued training of a variety of personnel from high school students to undergraduates and visiting scientists who will benefit from exposure to an integrative, collaborative research program. Results from these experiments will be incorporated into classroom teaching and general public outreach activities.