Holotype genome of the lesula provides insights into demography and evolution of a threatened primate lineage

The development of genome sequencing techniques has revolutionized evolutionary biology, facilitating the study of adaptation and speciation at the genome level. Genomic data has also become a cornerstone in conservation management, allowing inferences of population demography and genetic diversity. We sequence the genome of the holotype specimen of the elusive lesula (Cercopithecus lomamiensis), a recently described member of the guenons (tribe Cercopithecini), endemic to the Democratic Republic of the Congo. Using published and novel genomic data, we explore the evolutionary and demographic history of C. lomamiensis and its sister species C. hamlyni. We estimate that the two species split ca. 3–4 million years ago, and find that they both show high genetic diversity despite being listed as Vulnerable on the IUCN Red List. We identify signatures of positive selection in genes involved in pelage coloration and immune functions, as well as skeletal morphology and locomotor behavior, potentially related to the terrestrial lifestyle of C. lomamiensis and C. hamlyni, which stand out among the otherwise arboreal Cercopithecus genus. We specifically explore whether introgression from more distantly related terrestrial guenons was involved in the evolution of terrestriality in the hamlyni group, but found low molecular convergence suggesting that putative terrestrial adaptations occurred largely independently. This study provides insights into the demography and evolutionary history in a poorly known, threatened primate lineage. Furthermore, our results suggest that genomic erosion is not an imminent threat to these species, and that conservation management should prioritize actions to prevent further population decline.