Higher-Order Mechanisms in Olfactory Communication: Individual Recognition and Scent-Overmarking

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9724007 Johnston This proposal concerns mechanisms of olfactory perception and communication, particularly with regard to competition between individuals by scent marking. Most mammals communicate their individual identity and other information by scent marking, and many species that scent mark also scent over-mark (deposit their scent in the same location that other individuals have deposited scent). It has recently been discovered that, in at least two species of rodents, individuals can determine which of two individuals' scents is on top in an over-mark, regardless of whether the two scents are completely or only partially overlapping. Animals can thus determine which animal has marked most recently. The data suggest: (1) that the animals have a perceptual/cognitive strategy to determine which scent was deposited most recently; and (2) that they have some previously unsuspected sensory mechanisms to accomplish this. In this research, behavioral experiments will be carried out to investigate the functions of these extraordinary abilities, particularly with regard to the related hypotheses that (a) individuals engage in scent marking competitions in order to maintain their scent as the most recent scent in an area and (b) that other individuals evaluate scent over- marks as one means of assessing the quality of potential mates. Specifically, females may prefer males that are persistent at over-marking because this is a measure of male vigor and quality. These experiments will involve both typical laboratory tests using habituation-discrimination methods and other experiments using semi-natural laboratory enclosures to approximate the complexity of natural situations. In the specific context of the sense of smell and its role in animal behavior, this research will clarify the significance of a newly discovered ability to analyze spatial arrays of individual scents and determine which scent is on top (that is, to perceive "depth" or recen cy in arrays of individual odors). This perceptual ability probably occurs in many species and is potentially important in a wide range of situations. Our research aims to determine why such abilities have evolved, and to investigate the specific hypothesis that they are important in evaluation of the health, vigor, and quality of other individuals and thereby influence mate choice and competitive interactions. This project integrates mechanistic and functional approaches to olfactory communication. In a more general context, this research demonstrates some of the higher-order mechanisms involved in social perception and characterizes in a unique way the kinds of sophisticated processes animals may use to evaluate one another. Such higher-order knowledge of other individuals are widespread throughout the animal kingdom, which in turn suggests that this kind of evaluation of others has been important in the evolution of complex social behavior necessary for complex social organization. Understanding this kind of higher-order social cognition is necessary if we are to truly understand both the evolution of social communication and the neural mechanisms underlying social recognition, social memory, and social behavior in animals and in humans.