Maternal Pheromone Emission During Biparental Care: Evidence for Consistent Individual Differences and Links to Terminal Investment.

Pheromone production, once considered a fixed species-specific trait, is now recognized to vary plastically within individuals and consistently among them. Such variation may reflect differences in individual quality as well as adaptive allocation strategies, for example when residual reproductive value declines and individuals exhibit terminal investment in current reproduction. While most work has focused on sex pheromones, much less is known about variation in pheromones that mediate social behavior. In the burying beetle Nicrophorus vespilloides, caring females emit the pheromone methyl geranate (MG), which reflects their temporary infertility during active larval care and suppresses mating behavior of the male breeding partner. Here, we examined how MG emission varies with female age and reproductive experience, whether variation in emission reflects parental investment in the current brood, and whether it shows consistent individual differences. Females reproduced once or repeatedly at four ages under standardized conditions. Age alone did not affect MG emission, but pheromone levels and parental effort increased with reproductive experience. Importantly, MG emission was positively correlated with brood and larval mass, indicating that higher pheromone production was associated with greater investment in offspring. MG emission was also repeatable across reproductive bouts. These findings suggests that MG emission exhibits both plasticity and consistent individual differences and may serve as a reliable signal of maternal investment. MG could therefore provide males not only with information about female temporary infertility but also about her level of investment in the current brood, offering a mechanism for the coordination of parental care between the sexes.