Population genetics of the ABO locus within the rhesus (Macaca mulatta) and cynomolgus (M. fascicularis) macaque hybrid zone.

Knowledge of the macaque ABO blood group system has been critical in the development of nonhuman primates (NHPs) as a translational model. Serving not only as a useful homologue of the disease-linked ABO system in humans, macaque ABO blood groups must be typed in colonies prior to performing experimental procedures requiring blood transfusion or transplantation. While the rates of blood type incompatibility and the distributions of A, B and AB blood groups are known in large samples of rhesus (Macaca mulatta) and cynomolgus (M. fascicularis) macaques, there is a dearth of blood type data from macaque populations occupying the rhesus-cynomolgus hybrid zone in Southeast Asia. Using molecular phenotyping, we profiled ABO blood group distributions of 232 macaques from 10 populations in the hybrid zone and compared them to pure blood populations of the two species. We found that while these distributions are significantly different in most populations, there was a lack of differentiation between the hybrid and cynomolgus macaques as well as between the Thai and neighbouring populations. This supports a more expansive model of hybridization between rhesus and cynomolgus macaques than often proposed and highlights the increased need for consideration of population genetic structure in biomedical studies that employ macaques as animal models. Additionally, we report an enrichment of indeterminate blood types in the hybrid populations.