Prolactin Receptor Gene Diversity in Azara's Owl Monkeys (Aotus azarai) and Humans (Homo sapiens) Suggests a Non-Neutral Evolutionary History among Primates

Although paternal care is rare in mammals, males of several primate taxa exhibit high degrees of this behavior. Studies a number of vertebrate species found a positive correlation between prolactin (PRL) levels and paternal care. Studies of maternal care in knockout mice also indicate that the prolactin receptor (PRLR) plays a critical role in the neural regulation of parental care. To better understand the extent of PRLR genetic variation within primates, we characterized intraspecific coding variation in Azara's owl monkeys (Aotus azarai) from northern Argentina, a species with intensive paternal care. We then examined PRLR variation in 1088 humans (Homo sapiens) from the 1000 Genomes Project. Lastly, we assessed interspecific variation in PRLR in 4 different Aotus spp. and 12 phylogenetically (and behaviorally) disparate primate taxa. Our analyses revealed that the coding region of PRLR exhibits significant variation in all species of primates, with nonsynonymous amino acid substitutions being enriched in the intracellular domain, a region responsible for activation of downstream targets in the PRL pathway. In addition, several species exhibit entire codon deletions in this region. These results suggest a non-neutral evolutionary history of the PRLR locus within different primate lineages, and further imply that the translated PRLR protein has undergone considerable change throughout primate evolution. Such changes may be driven by selection for different behaviors and physiologies resulting from modulations of the pleiotropic prolactin pathway. Yet, the genetic variants in PRLR among primate taxa do not discretely cluster with species-level differences in paternal care behaviors. These observations imply that other mechanisms must be involved in the regulation of paternal care in primates.