Composition and compound proportions affect the response to complex chemical signals in a spiny lizard

Abstract: Most animal signals across sensory modalities are multicomponent traits that can be broken down into discrete elements. If different elements are perceived as unique, independent units (elemental perception), instead of as integrated percepts (configural perception), single changes in the presence/absence or the abundance of specific elements of a multicomponent signal may be enough to impact communication. Here, we found that male Yarrow’s spiny lizards (Sceloporus jarrovii) can discriminate single compounds of a multicomponent chemical signal (femoral gland secretions), different concentrations of a signaling compound, and a single compound from a mixture of compounds. In addition, one chemical compound elicited a response similar to that evoked by the complete natural scent. We conclude that perception of chemical signals in S. jarrovii lizards is elemental but also configural. The elemental perception of signaling compounds seems to occur with high sensitivity and narrow resolution, so that minor changes in single key elements may affect chemical communication. Given the multicomponent nature of most animal signals, hypotheses regarding signal function and evolution would be enhanced if researchers could determine whether these results apply to signals in other sensory modalities and identify the key elements of complex signals, from a receiver’s perspective. Significance statement: Most signals in animal communication are quite complex. For example, odors are mixtures of multiple volatile chemical compounds, and the way in which receivers perceive and process these mixtures to extract relevant information influences the structure and evolution of chemical signals. In a series of behavioral trials, we investigated how male Sceloporus jarrovii lizards may perceive conspecific odors by testing their response to individual and combined mixtures of two compounds present in femoral gland secretions at two different concentrations. We demonstrate that lizards can discriminate structurally similar compounds and that the response to a compound changes when said compound is part of a larger mixture. Compound concentration affected the perception of individual compounds but not complex mixtures. Deciphering what elements and/or configurations are perceived in an odor mixture is the only way to understand the role of mixture composition and its impact on communication.