Olfactory signals and the MHC: a review and a case study in Lemur catta

The major histocompatibility complex (MHC) is the most polymorphic genetic system known in vertebrates. Decades of research demonstrate that it plays a critical role in immune response and disease resistance. It has also been suggested that MHC genes influence social behavior and reproductive phenomena. Studies in laboratory mice and rats report that kin recognition and mate choice are influenced by olfactory cues determined at least in part by an individual's MHC genes. This issue has stimulated intense but controversial research. However, work in this field has only been carried out in rodents and humans. Thus far, no study has directly investigated the relationship between olfactory cues and MHC genotype in nonhuman primates. Furthermore, other genetic loci, including those linked to the MHC, have not been ruled out as the primary influence on odor profiles. To explore the relationship between individual odor profiles and MHC alleles, we are studying ring-tailed lemurs (Lemur catta). These animals are an ideal model species because they are extremely scent-oriented and their behaviors suggest that olfactory signals form an important part of their intra- and intergroup communication systems. Individual odor profiles from tail and scent gland samples were generated for six males using gas chromatography mass spectrometry (GC-MS). MHC genotypes were identified using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE). The GC-MS analyses demonstrated a difference between profiles obtained from tail and scent gland samples. Although our sample size is relatively small and statistical significance could not be obtained, our analyses suggest a relationship between MHC and concentrations of volatile compounds. While these results are preliminary, they support the need for further studies of the MHC and olfactory signals in lemurs and other primates.