The scent of inbreeding: male sex pheromones betray inbred males

Inbreeding depression results from mating among genetically related individuals
and impairs reproductive success. The decrease in male mating
success is usually attributed to an impact on multiple fitness-related traits
that reduce the general condition of inbred males. Here, we find that the production
of the male sex pheromone is reduced significantly by inbreeding in
the butterfly Bicyclus anynana. Other traits indicative of the general condition,
including flight performance, are also negatively affected in male
butterflies by inbreeding. Yet, we unambiguously show that only the production
of male pheromones affects mating success. Thus, this pheromone
signal informs females about the inbreeding status of their mating partners.
We also identify the specific chemical component, hexadecanal, probably
responsible for the decrease in male mating success. Our results advocate
giving increased attention to olfactory communication as a major causal
factor of mate-choice decisions and sexual selection.