Genetic Diversity and Population Structure of the Southern Black-Horned Capuchin (Sapajus nigritus cucullatus) in Argentina.

This study estimates the genetic variability of remaining populations of southern black-horned capuchin (Sapajus nigritus cucullatus) in the Atlantic Forest of Misiones, Argentina and assess connectivity to identify priority conservation units. We evaluated 59 microsatellite loci previously described for other primates, including humans, of which 16 were polymorphic. A total of 81 individuals were genotyped, comprising 33 tissue samples from rescue centers, 3 from capture for radiocollar placement, and 45 non-invasive fecal samples from two wild populations: Yacutinga Reserve (Fragmented Forest, FF) and the Urugua-í-Forester Biological Corridor (Continuous Forest, CF). Structure analysis identified an optimal value K = 3, revealing three major genetic ancestry components with varying degrees of admixture across populations rather than discrete lineages. These components correspond to: (1) a distinctive Continuous Forest (CF) component, (2) a distinctive Yacutinga Fragmented Forest (FF) component, and (3) a widespread background component occurring throughout Misiones Province, which represents the entire distribution range of the species in Argentina. Notably, the CF population exhibited the highest genetic variability, whereas FF showed the lowest. Isolation-by-distance analysis via the Mantel test revealed no significant relationship between genetic and geographic distances (R = 0.0336; p = 0.299), suggesting that genetic differentiation may be driven by habitat fragmentation and landscape characteristics rather than geographic distance alone, though historical demographic dynamics may also contribute to these patterns. These results emphasize that forest fragmentation negatively impacts the genetic health of S. n. cucullatus and underscore the urgent need to maintain and restore biological corridors to ensure long-term genetic viability in the fragmented landscape of Misiones.