Genomic Insights into Derived Dwarfism and Exudivory in a Genus (Callithrix) of the World's Smallest Anthropoid Monkeys

The primate Callitrichidae family represents the smallest anthropoid primates, which are known to possess dietary specializations for eating viscous plant exudates (exudivory), and as callitrichids Callithrix marmosets push these biological traits to extremes. Using low-coverage whole genome sequencing of Callithrix species, we investigated Callithrix evolutionary history, species genetic diversity, and the genomic basis of derived small body size and exudivory. Our phylogenetic species tree shows that Callithrix likely originated in southeastern Brazil and migrated northward to the semi-arid regions of central and northeastern Brazil. We show that there is greater genetic similarity between smaller and more exudivorous Callithrix species relative to larger and less exudivorous species, and that the genus likely experienced extensive past reticulation. Based on these results, we argue that the Callithrix migration from the Atlantic Forest biome to the relatively more extreme environments of Cerrado/Caatinga biomes progressively reduced body size and increased exudivory specialization in Callithrix marmosets. We also identified species-specific candidate genes under putative positive selection for traits that include body growth, bone development, reproduction, fat metabolism, insulin signaling, and liporegulation. In conclusion, we increased genomic resources for understudied Callithrix species, while providing the most comprehensive overview of marmoset genomic diversity to-date, and identify several candidate genes under positive selection for traits related to small body size and exudivory. Future studies should sample wild marmosets more widely and perform higher-coverage genomic sequencing to better understand how specific genomic variants may impact the evolution of key Callithrix biological traits.