Pheromone isoform composition differentially affects female behaviour in the red-legged salamander, Plethodon shermani

Pheromones are a diverse class of biological molecules that play critical roles in mediating social and sexual behaviours. In many systems, pheromones exist in complex mixtures, with the precise composition and ratios of the different components essential for bioactivity. The interactive effects of complex pheromone mixtures, however, have been minimally studied in vertebrates. In the red-legged salamander, male salamanders use nonvolatile proteinaceous pheromones to modify female courtship behaviour and mating receptivity. One component of this pheromone mixture is a hypervariable 7 kDa protein, plethodontid modulating factor (PMF). Within a single population, individual male salamanders express more than 30 variants (isoforms) of PMF. While the complete pheromone secretion increases female mating receptivity, a subset of PMF isoforms was demonstrated to reduce receptivity. In the current study, we demonstrated that a single PMF isoform had no effect on female mating behaviour, while a more complete mixture of PMF variants recapitulated the effect of the whole pheromone mixture and increased female receptivity. From these data, we hypothesize (1) that female preference and sexual selection have promoted the rapid gene duplication of PMF over ∼20 MY, resulting in the complex mixture we observe today and (2) that PMF isoforms act synergistically through complex neurophysiological pathways to modulate female courtship behaviour. These studies help define a framework for further investigations of the complex interactions and molecular mechanisms by which protein pheromones modulate female mating behaviour.