Message ‘scent’: lemurs detect the genetic relatedness and quality of conspecifics via olfactory cues

To enhance the fitness benefits of social and sexual interaction, animals should be able to decipher information about the genetic makeup of conspecifics. The use of relative criteria to estimate genetic relatedness could facilitate nepotism or inbreeding avoidance, and the use of absolute criteria to estimate genetic quality could help identify the fittest competitor or the best mate. For animals to process trade-offs between relatedness and quality, however, both relative and absolute genetic information must be concurrently available and detectable by conspecifics. Although there is increasing evidence to suggest that animals make genetically informed decisions about their partners, and may even process trade-offs, we understand relatively little about the sensory mechanisms informing these decisions. In previous analyses of the olfactory signals of ringtailed lemurs, Lemur catta, we showed that both scrotal and labial secretions seasonally encode chemical information about (1) pairwise genetic relatedness, within and between the sexes, and (2) individual heterozygosity. Here, using a signaller–receiver paradigm, we conducted behavioural bioassays to test whether male and female lemurs are sensitive to these olfactory sources of genetic information in unfamiliar conspecifics. As the lemurs discriminated conspecific glandular secretions by pairwise relatedness and individual heterozygosity, volatile olfactory signals can be used by both sexes to concurrently process relative and absolute genetic information about conspecifics. Beyond supporting an olfactory mechanism of kin discrimination and mate choice in a primate, we suggest that animals could use olfactory processing to trade off between selection for the most compatible partner versus the most genetically diverse partner.