NSF-BSF: Exploiting the evolution of odorant discrimination in ants to decipher the olfactory code

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One of the properties of life is the ability to detect and respond to environmental stimuli, which is facilitated in animals by sophisticated sensory systems such as vision, audition, and olfaction. However, compared to vision and audition, large gaps exist in our understanding of olfactory space and the evolution of odor discrimination. This project investigates the interplay between odors and their specific receptors by using ants as a new olfactory model system to help decipher the olfactory code. Ants depend on their olfactory sense to communicate with each other and to differentiate between colony members or non-members. For this purpose, they use chemicals that occur on their body surface and that provide a large vocabulary of chemical “words”. Their importance in ants is reflected in the large repertoire of olfactory receptors that are sensitive to these compounds. Discrimination bioassays, analyses of olfactory receptor tuning to these compounds, analyses of receptor evolution and a structure/function analysis of the olfactory receptors will decipher how discrimination of compounds can be improved at the receptor level. The outcome of this research will help fill a gap in our fundamental understanding of olfaction and communication through olfaction. The project will be used to train undergraduate and graduate students as well as high-school students from underrepresented groups in modern approaches of behavioral analysis and experimentation. An educational game about olfactory discrimination will be produced that can be integrated into classroom lessons for high school students.Understanding the mechanisms of odorant discrimination is still a challenging problem in the sensory physiology of animal behavior that includes the receptor level and the processing of olfactory information in higher brain centers. This project focuses on mechanisms of odorant discrimination at the receptor level and uses the compound group of cuticular hydrocarbons for this purpose. Cuticular hydrocarbons occur as complex mixtures of long-chain hydrocarbons on the body surface of almost all insects and are used in many important contexts, including mate communication and colony discrimination, which require classification of individuals based on their cuticular hydrocarbon profiles. In social insects, discrimination against non-colony members is especially important to avoid any form of colony exploitation. Therefore, strong selection on these discrimination abilities is expected in social insects. The rich olfactory receptor repertoire in ants will be exploited to identify key receptors in the discrimination of cuticular hydrocarbons. Tuning curves of these hydrocarbon sensitive olfactory receptors will be determined and compared. These analyses will be combined with bioassays to determine differences in the discrimination of individual hydrocarbon compounds. The abundance of cuticular hydrocarbon sensitive olfactory receptors in the receptor phylogeny of ants, and the presence of many closely related olfactory receptors following gene duplications, provide the foundation of structure/function analyses. The combination of functional analyses of ligand specificity of closely related olfactory receptors with the three-dimensional reconstruction of the receptor molecules will establish how molecular sequence changes lead to the expansion of olfactory space.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.