On the validity of Plecturocebus parecis Gusmão et al., 2019, a titi monkey described from southwestern Brazilian Amazonia

Plecturocebus parecis was described from the southwestern Brazilian Amazon, but its taxonomic status was subsequently questioned after mitochondrial evidence prompted alternative hypotheses regarding species limits within this complex. We reassessed these hypotheses using 57 occurrence records obtained from 47 localities during 18 field expeditions conducted between 2023 and 2025. Morphologically homogeneous populations exhibiting the diagnostic phenotype of P. parecis occupied a broad geographic area centred on the Juína region, whereas intermediate phenotypes were geographically restricted to peripheral portions of the distribution, particularly within the Comemoração and Roosevelt drainages. This spatially structured pattern of phenotypic variation provides stronger support for the interpretation of P. parecis as a geographically cohesive and diagnosable lineage than for hypotheses proposing a broadly hybrid population lacking taxonomic cohesion. The distributions of P. parecis, P. cinerascens, and P. bernhardi were also geographically structured, with only limited areas of potential contact. Although additional nuclear genomic and cytogenetic data remain necessary to distinguish among alternative evolutionary scenarios, our results provide a stronger empirical basis for evaluating the recognition of P. parecis while highlighting the importance of comprehensive geographic sampling when evaluating species boundaries in Amazonian primates.