The oxytocin (OT) hormone pathway is involved in numerous physiological processes, and one of its receptor genes (OXTR) has been implicated in pair bonding behavior in mammalian lineages. This observation is important for understanding social monogamy in primates, which occurs in only a small subset of taxa, including Azara’s owl monkey (Aotus azarae). To examine the potential relationship between social monogamy and OXTR variation, we sequenced its 5′ regulatory (4936bp) and coding (1167bp) regions in 25 owl monkeys from the Argentinean Gran Chaco, and examined OXTR sequences from 1092 humans from the 1000 Genomes Project. We also assessed interspecific variation of OXTR in 25 primate and rodent species that represent a set of phylogenetically and behaviorally disparate taxa. Our analysis revealed substantial variation in the putative 5′ regulatory region of OXTR, with marked structural differences across primate taxa, particularly for humans and chimpanzees, which exhibited unique patterns of large motifs of dinucleotide A+T repeats upstream of the OXTR 5′ UTR. In addition, we observed a large number of amino acid substitutions in the OXTR CDS region among New World primate taxa that distinguish them from Old World primates. Furthermore, primate taxa traditionally defined as socially monogamous (e.g., gibbons, owl monkeys, titi monkeys, and saki monkeys) all exhibited different amino acid motifs for their respective OXTR protein coding sequences. These findings support the notion that monogamy has evolved independently in Old World and New World primates, and that it has done so through different molecular mechanisms, not exclusively through the oxytocin pathway.
