Sex pheromone signal and stability covary with fitness

If sexual signals are costly to produce or maintain, covariance between signal expression and fitness is expected. This signal-fitness covariance is important evolutionarily, because it can contribute to the maintenance of genetic variation in signal traits, despite selection from mate preferences. Chemical signals, such as moth sex pheromones, have traditionally been assumed to be stereotypical species-recognition signals, but their relationship with fitness is unclear. Here we test the hypothesis that for chemical signals that are primarily used for conspecific mate finding, there is covariation between signal properties and fitness in the noctuid moth Heliothis subflexa. Additionally, as moth signals are synthesized de novo every night throughout the females reproductive life, the maintenance of the signal can be costly. Therefore, we also hypothesized that fitness covaries with signal stability (i.e. the lack of intra-individual variation over time). We measured among- and within-individual variation in pheromone amount and composition as well as fecundity, fertility, and fitness in two independent groups of females that differed in the time in between two consecutive pheromone samples. In both groups, we found reproductive success and longevity to be correlated with pheromone amount, composition, and stability, supporting both our hypotheses. This study is the first to report a correlation between fitness and sex pheromone composition in moths, solidifying previous indications of condition-dependent moth pheromones and highlighting how signal-fitness covariance may contribute to heritable variation in chemical signals both among and within individuals.