Phylogeography and niche modeling of night monkeys (Aotus) in northwestern South America

Cryptic species are genetically distinct but morphologically similar lineages, frequently found in geographically complex regions where mountains and rivers serve as isolating barriers. In American primates, such as night monkeys (Aotus), cryptic speciation has been proposed but remains poorly understood due to limited sampling. In northwestern South America, members of the Aotus lemurinus complex (A. griseimembra, A. lemurinus, and A. zonalis) have been assumed to occupy distinct elevations, although no clear geographic boundaries have been identified. To clarify their evolutionary relationships, we integrated mitochondrial DNA data from 93 sites, ecological niche modeling, and analyses of hair length variation. Phylogenetic analyses recovered four major clades—one cis-Andean and three trans-Andean—showing strong geographic structure largely associated with the Magdalena River. Riverine barriers, rather than elevation, appear to have played a primary role in lineage divergence. Ecological niche modeling revealed potential distributions on opposite riversides across a broad elevational gradient, with a narrow zone of potential sympatry in the lower section of the Magdalena River. Niche similarity tests indicated no significant ecological divergence between clades. Hair length increased with elevation in wild populations inhabiting both the Central and Oriental Cordilleras of the Colombian Andes, on opposite sides of the Magdalena River suggesting convergent morphological responses to highland ecosystems. These findings challenge previous taxonomic hypotheses that separated A. griseimembra and A. lemurinus by elevation and instead emphasize the role of riverine isolation—particularly along the upper and middle sections of the Magdalena River—in shaping the diversification of Aotus in Northern South America.