Role of Rivers as Geographical Barriers in Shaping Molecular Divergence of Neotropical Primates

ABSTRACT We quantitatively tested the riverine barrier hypothesis and its influence on biogeographical distributions and molecular variation in New World monkeys (Parvorder: Platyrrhini). Using mitochondrial markers (cytochrome oxidase subunit II and cytochrome b), we analyzed taxonomic differences and the effects of geographical barriers on molecular patterns across Central and South America. Nearly 80% of described species are separated by geographical barriers, including several mountain chains. River width exhibited a negative correlation with molecular similarity in adjacent taxa for both molecular markers. Several presently described taxa were not supported based solely on these molecular phylogenetic markers, including Saimiri , Mico , Cebus , Sapajus , and Cherecebus . These taxonomic issues are far more common where river barriers do not exist. In conclusion, we found a significant correlation between river width and molecular divergence in adjacent taxa, indicating that wider rivers were associated with greater molecular divergence for two commonly used mitochondrial genes. Species boundaries were predominantly found at river interfaces, and in the absence of discernable geological barriers, adjoining species were more likely to exhibit molecular similarity. Our findings suggest that river and mountain barriers are significantly associated with gene flow for neotropical primate taxa. Additionally, river width proves to be a valuable tool for estimating molecular divergence in adjacent taxa, particularly in regions with limited sampling.