Genetic diversity and structure in Saimiri macrodon Elliot (Primates, Cebidae) across a disturbed and an undisturbed habitat in Sucumbíos, Ecuador

The Ecuadorian squirrel monkey (Saimiri macrodon) is listed as Least Concern by the International Union for Conservation of Nature (IUCN). However, its long-term viability is threatened by deforestation and habitat fragmentation. This study investigated the genetic diversity and structure of two S. macrodon populations in disturbed (Shushufindi) and undisturbed (Cuyabeno) habitats in Sucumbíos Province, Ecuador. DNA extracted from fecal samples was analyzed at five microsatellite loci. Results showed a high genetic diversity of this primate (Ho = 0.336, HT = 0.801, Na = 8.250) and a moderate genetic differentiation (FST = 0.061), with 6% of the genetic variation found among populations and 94% within populations and individuals. Both populations exhibited a deficit of heterozygotes, indicated by positive inbreeding coefficients (FIS = 0.702). Despite these findings, high genetic diversity likely results from disruptive selection, favouring homozygotes for distinct alleles in each population. STRUCTURE analysis revealed two genetic clusters with partial overlap between populations. These findings highlight the impact of habitat disturbance on genetic structure and underline the importance of conserving both populations.